Construction Materials doi: 10.3390/constrmater6030037

Authors: Paula Abdo-Peralta Nestor Ulloa Evelin Rosero Kerly Mishell Vaca Vallejo Mauricio Chavez Christian Rolando Zapata León

This study investigates the effect of nano-zeolite and lime on the resistance of reconstituted soil using an integrated experimental and explainable machine learning framework. Soil samples were prepared with varying proportions of nano-zeolite, lime, and fines, and cured under controlled temperature and time conditions. Soil resistance (q) was measured to evaluate the mechanical performance of each mixture. Eight machine learning models, including artificial neural networks (ANN), random forest (RF), random tree (RT), random committee–random tree (RC-RT), M5Rules, KStar, RBFS, and additive regression–decision stump (AR-DS), were developed using Weka 3.8.6 to predict soil resistance based on the input parameters. Model performance was assessed using SSE, MAE, MSE, RMSE, Error %, Accuracy %, R2, correlation coefficient, Willmott Index, Nash–Sutcliffe Efficiency, Kling–Gupta Efficiency, and SMAPE. ANN and RF achieved superior accuracy (R2 ≥ 0.98) with minimal prediction error, effectively capturing the nonlinear interactions between stabilizer content, curing time, and environmental conditions. Sensitivity analyses using the analysis index and SHAP values revealed that nano-zeolite, lime, and curing time were the dominant factors influencing soil resistance, while fines content and curing temperature had secondary effects. The results demonstrate that nano-zeolite and lime significantly enhance soil resistance and that explainable machine learning models can reliably predict and interpret soil performance, providing a data-driven framework for optimized soil stabilization in geotechnical engineering applications.

Construction Materials doi: 10.3390/constrmater6030036

Authors: Aras Arslan Mustafa Gencoglu Arastoo Khajehdehi

This study experimentally investigates the structural behavior of hexagonal- and square-shaped composite specimens subjected to vertical compression, vertical tension, and diagonal tension loading. The specimens were fabricated using four- and six-layer alkali-resistant (AR) glass textile reinforcements embedded in a modified cementitious mortar via pull, pour, and roll manufacturing techniques. The mechanical performance of polyvinyl alcohol (PVA) fiber-reinforced composite connectors and steel clamp-type elements was also evaluated at the joints of hexagonal specimens under vertical tension and lateral shear loading. The results show that increasing the number of textile layers significantly enhances structural performance. A 50% increase in textile layers improved load-carrying capacity by up to 56% in compression, 104% in tension, and 216% in diagonal tension. Corresponding increases of approximately 20–42% in ductility and up to 266% in energy dissipation capacity were observed. No failure occurred in the connecting elements, confirming their adequate stiffness, strength, and ductility. In addition, validated three-dimensional finite element models were developed to simulate the response of the hexagonal specimens. Overall, the proposed system demonstrates strong potential for applications such as infill walls, cladding, and sandwich panels due to its favorable strength, ductility, and energy absorption capacity.

Construction Materials doi: 10.3390/constrmater6030035

Authors: Sena Tayfur Ninel Alver

The abrupt failure of shear-deficient RC beams may lead to harmful consequences under dynamic loading. The use of Carbon Fiber Reinforced Polymers (CFRP) aims to convert this brittle fracture into a ductile one. However, the complexity of the multiple damage mechanisms makes it difficult to assess their condition using conventional testing methods. In this study, the damage evolution of a shear-critical reference beam and its CFRP-strengthened counterpart was monitored using the acoustic emission (AE) technique. After correcting attenuated AE amplitudes, damage analysis was performed using the Shannon entropy approach based on true source amplitudes. The entropy analysis performed with these corrected data clearly revealed the shear failure in the reference beam through abrupt drops in entropy, indicating damage homogenization. In contrast, the entropy remaining high and dynamically varying over a much longer deflection range in the CFRP-strengthened beam demonstrated that CFRP distributes damage over a wider region and that different damage mechanisms, such as debonding and fiber breakage, in addition to concrete cracking, were simultaneously active.

Construction Materials doi: 10.3390/constrmater6030034

Authors: Amjad H. Albayati Hasan M. Al-Mosawe Ahmed M. Mohammed Mayank Sukhija Aliaa F. Al-ani Mazen J. Al-Kheetan Mustafa M. Moudhafar

The performance and durability of asphalt pavements are strongly influenced by the rheological properties of asphalt binders, particularly under severe climatic and traffic conditions. This study investigates the synergistic effects of incorporating multi-walled carbon nanotubes (CNTs) at dosages ranging from 0.25% to 1% into AC 40-50 asphalt binders modified with 4% Styrene–Butadiene–Styrene (SBS). A comprehensive experimental program involving physical, rheological, and chemical characterization tests was conducted, including penetration, softening point, viscosity, storage stability, a Dynamic Shear Rheometer (DSR), Multiple Stress Creep Recovery (MSCR), Linear Amplitude Sweep (LAS), Fourier Transform Infrared Spectroscopy (FTIR), and Glover-Rowe (G-R) analysis. Statistical inference using one-way ANOVA was also conducted to evaluate the significance of differences among the binder formulations investigated. The results showed a continuous increase in binder stiffness with increasing CNT content, as indicated by decreasing penetration values, higher softening points, and increased viscosity. Incorporating 1% CNT reduced the softening-point difference from 3.1 °C to 1.6 °C in SBS-modified binders, indicating improved storage stability. Rheological evaluations showed that 0.75% CNT increased the high-temperature performance grade from 82 °C to 88 °C and provided the best rutting resistance, as indicated by MSCR results. In contrast, the 0.5% CNT formulation exhibited superior fatigue resistance and the lowest Glover-Rowe index, indicating improved cracking resistance and durability. Overall, the findings demonstrate that CNTs can effectively enhance the performance of SBS-modified asphalt binders, with 0.75% CNT being optimal for hot-climate applications, while 0.5% CNT exhibited improved fatigue and cracking resistance under moderate-temperature conditions.

Construction Materials doi: 10.3390/constrmater6030033

Authors: Eric J. Faierson Benjamin D. Nelson Elizabeth S. Poblete

The integration of advanced additive manufacturing technologies, particularly 3D printing (3DP), also known as Additive Construction (AC), could influence a shift in the construction industry towards improved efficiency and automation. This research evaluated the effect on hardened properties of two different concrete mixes for use in 3DP based on the presence or absence of alkaline-resistant (AR) glass fibers. Furthermore, three different curing methods were evaluated: air-curing, plastic-covered curing, and spray-curing. Concrete beams were printed for flexural testing, and cores were taken from other depositions to evaluate compressive strength and split-tensile strength. An analysis of the size and location of cracks on the beams after curing was performed for the different mixes and curing methods. For beams without fibers, plastic-covered curing produced the highest flexural modulus values, and air-curing produced the lowest flexural modulus values. Plastic-cured beams with fibers had higher flexural modulus values than the air-cured beams with fibers. However, the spray-cured beams with fibers produced somewhat anomalous results, with one flexural modulus value being larger than those of the plastic-cured beams, and the other flexural modulus value being less than those of the air-cured beams. All 28-day compressive strengths and split-tensile strengths across mixes and curing conditions fell within a small band ranging between ~19.3–22.1 MPa and ~1.7–2.0 MPa (~2800–3200 psi, and 240–290 psi), respectively. There was a large amount of scatter in some of the tests. It appears that neither the presence of the AR-glass fibers, nor the type of curing had a large influence on compressive strength or split-tensile strength. Results showed that the addition of fibers and the use of the plastic during curing significantly reduced the occurrence, the width, and the depth of cracks as a result resulting from the curing process. Plastic-curing was the most effective curing method for minimizing the occurrence of cracks. Any cracks that formed during plastic-curing were extremely fine and had little or no effect on mechanical properties.

Construction Materials doi: 10.3390/constrmater6030032

Authors: Ali Alzahrani Mithila Achintha

Seawater and sea sand as constituents in concrete are valuable alternatives to freshwater and river sand. Further, the use of seawater and sea sand in projects located in the proximity of a sea/ocean can reduce the overall project cost and lower the carbon footprint. Nevertheless, seawater contains high concentrations of chloride (Cl−), sulphate (SO42−) and magnesium (Mg2+), which can react with tricalcium aluminate (C3A) in cement and the byproduct calcium hydroxide (Ca(OH)2), and form Friedel’s salt, delayed ettringite and brucite, respectively. These chemical compounds are aggressive and can degrade the strength and durability of the concrete. Differences in the physical properties of sea sand compared to river sand can also lead to weak and porous concrete. In reinforced concrete, steel bars are susceptible to corrosion due to the formation of corrosion products as a result of high concentrations of Cl−. Whilst mitigation strategies such as the use of supplementary cementitious materials (SCMs) and fibre-reinforced polymer (FRP) reinforcements have been investigated in the literature, no validated method that enables the use of concrete with seawater and sea sand has been established. Based on research reported in the literature, the present study investigates the chemistry, strength and microstructure of concrete mixed with seawater and sea sand as a means of establishing their use in concrete without compromising the properties of the concrete. The study shows that the compressive strength of seawater–sea sand mixed concrete (SWSSC) is increased in the short term (up to 28 days) due to the formation of additional chemical compounds in the former. However, the long-term (i.e., beyond 28 days) compressive strength of concrete reduces by up to 20% after one year due to the weakening of the microstructure (more flaws/expansions), which further reduces the durability of the reinforced concrete. Although the long-term degradation of SWSSC has been noticed, the underlying causes are not fully understood. The present critical review study provides chemical and microstructural insight into the degradation of concrete with seawater and sea sand, and the current developing understanding is used to develop a mitigation strategy towards the use of seawater and sea sand in real-world concrete applications.

Construction Materials doi: 10.3390/constrmater6030031

Authors: Mohamad Ali-Ahmad Christina El Sawda Amenah AlFailakawi Nourah AlKhaldi Sarah AlMajed Malak Sughayer Nourah AlZuabi

This study investigates the effect of mass-based replacement of natural coarse aggregate with electric arc furnace (EAF) slag on the performance of ordinary Portland cement (OPC) concrete. Replacement levels of 0%, 30%, 50%, and 100% were examined, with particular attention to the volumetric changes induced by the higher density of EAF slag, which leads to an increase in paste volume. Fresh, mechanical, durability-related, and microstructural properties were evaluated. Results show a continuous reduction in workability with increasing slag content, despite the increase in paste volume, indicating the dominant influence of aggregate morphology on rheological behavior. Mechanical performance exhibited a non-linear response. Within the tested series, the 50% replacement mixture showed the highest mean compressive and splitting tensile strengths; however, the compressive strength difference relative to the control mixture remained small and within typical experimental scatter. In contrast, water absorption decreased progressively, reflecting improved matrix densification. However, this densification did not translate into enhanced mechanical performance, highlighting a decoupling between durability-related indicators and strength. A screening-level CO2 assessment further showed that reductions in aggregate-related emissions were offset by increased cement content associated with mass-based replacement. The results emphasize the importance of considering volumetric effects when interpreting the behavior and sustainability of slag-based concrete. Note: all strength comparisons are based on mean values from three-specimen sets without formal statistical testing and should be regarded as exploratory observations.

Construction Materials doi: 10.3390/constrmater6030030

Authors: Franziska Vogt Andrea Osburg

The formation of blisters in reactive resin coatings on concrete is a widely known phenomenon that is also a subject of debate in the literature. In particular, blisters forming after curing of the coating can lead to extensive damage. This study was focused on the investigation of blistering between the concrete substrate and the resin coating. The hypothesis is that the cementitious material and the overlying reactive resin coating form a system that leads to damage under certain boundary conditions regarding material composition, as well as moisture and mass transport. Systematic investigations were carried out in an extensive testing program with various substrate mortars that differ in cement type, water–cement ratio, and aggregate. As coating systems, two different EP primers were used with a transparent EP topcoat. The long-term testing was conducted on potential blistering of composite test specimens stored under various (practically relevant) conditions prior and after the coating. It was found that a higher moisture content of the substrate reduces blistering of the EP coating system. EP systems containing benzyl alcohol do not automatically tend to blister. Furthermore, condensation in the substrate provides sufficient amounts of water to cause blistering and ASR can contribute to blister formation.

Construction Materials doi: 10.3390/constrmater6030029

Authors: Nisal Dananjana Rajapaksha Mehrdad Ameri Vamkani Michaela Gkantou Francesca Giuntini Ana Bras

Recycled aggregates (RAs) from construction and demolition waste (CDW) provide substantial circular-economy benefits, yet their elevated porosity, adhered mortar, and heterogeneity typically impair the mechanical performance and durability of recycled aggregate concrete (RAC). This PRISMA 2020-compliant systematic review synthesises 2180 records (2015–2026) to evaluate advanced strategies for enhancing RA quality prior to structural use. This paper critically compares removal-based treatments (mechanical, thermal, acid cleaning) with strengthening and densification approaches, including accelerated carbonation, pozzolanic and nano-silica coatings, polymer impregnation, microbial-induced calcium carbonate precipitation (MICP), and modified mixing methods such as triple-stage mixing (TSMA). Evidence shows that while all RA types (including recycled fine aggregate (RFA), recycled coarse aggregate (RCA), and their combination (RFCA)) can slightly reduce compressive strength and 30% replacement serves as a critical threshold, beyond this, strength loss accelerates, particularly in RCA and RFCA mixes. However, accelerated carbonation and TSMA consistently refine the interfacial transition zone, reduce water absorption by 17–30%, and recover 85–94% of natural aggregate concrete strength. Bio-deposition reduces water absorption by 13–21%, while acid/silica fume treatments improve late-age strength but carry environmental trade-offs. This review formulates a practice-oriented implementation framework for structural-grade RAC. Sustainability analyses indicate that carbonated RA can achieve net-positive CO2 abatement when under low-carbon energy supply. A mechanistic schematic is presented to synthesise treatment-to-pore-structure/durability pathways across the four principal treatment routes, and a quantitative synthesis plot compares water absorption reductions across all treatment types using 13 data points drawn from included studies. A structured treatment comparison evaluates the energy intensity, industrial scalability, CO2 footprint, and technology readiness level for each strategy. The remaining challenges include a lack of hybrid treatment studies, limited real-scale durability data, and insufficient mechanistic models linking treatment to pore structure evolution. This review recommends harmonised durability-based criteria and updates to standards (e.g., BS 8500, EN 12620) to support the scalable deployment of treated RA.

Construction Materials doi: 10.3390/constrmater6030028

Authors: Tamim A. Samman Khatib Zada Farhan Md Ashraful Hossain

Drying shrinkage is a critical durability issue in concrete structures, particularly in high-strength concrete (HSC), which is more susceptible to early-age cracking due to its low water–cement ratio and dense microstructure. This study experimentally evaluates the restrained drying shrinkage behavior of fiber-reinforced concretes with compressive strengths ranging from 23 to 84 MPa, employing a total of 84 ASTM C1581 ring specimens exposed to three exposure conditions: outdoor climate, indoor laboratory conditions (25 °C, 50% RH), and a controlled chamber (50 °C, 30% RH). Plain concretes exhibited increasing shrinkage with both strength and environmental severity. Under indoor exposure, 90-day shrinkage reached approximately 660 × 10−6 (23 MPa), 291 × 10−6 (40 MPa), 753 × 10−6 (60 MPa), and 338 × 10−6 (84 MPa), with high-strength mixes showing greater cracking susceptibility. Fiber incorporation significantly mitigated both strain and cracking in a dosage-dependent manner. Steel fibers at 1.0–1.5% reduced shrinkage by up to 75% in 40–60 MPa concretes, while polypropylene fibers at 0.25–0.5% achieved reductions up to 66% and eliminated cracking in several cases. Results demonstrate that concrete strength, exposure condition, fiber type, and dosage collectively govern shrinkage and cracking resistance.

Construction Materials doi: 10.3390/constrmater6030027

Authors: Lukas Steffen Ismael Viejo Belén Hernández-Gascón Mario Stelzmann Klaus Holschemacher Robert Böhm

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Construction Materials doi: 10.3390/constrmater6030026

Authors: Mustafa Al-Bazoon Saba Jasim Al-Rubaye Faten I. Mussa Abdulkhaliq A. Jaafer Lateef Assi Mohanad M. Abdulazeez

In designing tall buildings, the primary concern is ensuring an effective lateral load-resisting system in addition to the gravity load system, since it largely governs the overall design. This study investigates the influence of X-cable bracing on the structural weight of tall steel frame buildings subjected to service and wind loading. Three numerical case studies, 10-story, 20-story, and 30-story planar steel frames, were modeled and analyzed using SAP2000, then optimized using Differential Evolution (DE) and Enhanced Colliding Bodies Optimization (ECBO) algorithms. These designs were evaluated under both service and wind load conditions, considering strength and drift constraints. The results indicate that the inclusion of wind loads in addition to service loads leads to a higher total structural weight than considering service loads alone, while cable bracing effectively reduces the overall mass by up to 6%, 38%, and 20% for the 10-story, 20-story, and 30-story frames, respectively, compared to unbraced structures, by improving the internal force distribution among structural components. Strength demands, reflected by the interaction ratio, governed all design cases, while lateral displacement was always less than the maximum limit according to AISC and ASCE requirements. Overall, the results highlight the potential of cable bracing systems to deliver efficient tall building designs; however, further studies are needed to generalize these findings to a broader range of building configurations.

Construction Materials doi: 10.3390/constrmater6030025

Authors: Jean-Pierre Giroud

Concrete linings are used for water containment, in particular in reservoirs and canals. When the soil underlying a concrete lining has a high permeability, seepage into the ground of water from concrete-lined reservoirs and canals is essentially governed by leakage of water through the concrete linings. Therefore, it is essential to properly evaluate the hydraulic conductivity of concrete linings. It is known that cracks generally develop in concrete linings. This article provides material data and a method for the evaluation of the hydraulic conductivity of concrete linings, in particular cracked concrete linings, through two approaches. The first approach consists of a review of selected published values of the measured hydraulic conductivity of intact and cracked concrete. The second approach consists in developing an original analytical method to determine the hydraulic conductivity of cracked concrete using the results of an experimental evaluation of the influence, on water flow, of the tortuosity and rugosity of concrete cracks. The results obtained with the two approaches are compared and numerical examples are presented. Based on these results, practical guidance is provided to design engineers for a safe evaluation of the hydraulic conductivity of concrete linings, cracked or not cracked.

Construction Materials doi: 10.3390/constrmater6030024

Authors: Rauan Lukpanov Matija Orešković Artem Chystiakov Duman Dyussembinov

In this study, the characteristics of concretes made from mixed recycled aggregate—the cheapest and most common secondary raw material in construction and demolition waste—were determined. For this study, besides experimental concretes using mixed recycled aggregate, reference compositions were developed using river gravel, recycled concrete aggregate, and recycled masonry aggregate. The workability of concrete mixtures was measured as class S1, which is acceptable for use with slipform concrete pavers, and was achieved by varying the water/cement ratio, considering the different water adsorptions of the concrete fillers. The following mechanical characteristics of the concretes were defined on the 3rd and 28th days: density, compressive strength, flexural strength, water absorption, and frost resistance. The test results showed sufficiently high indicators of strength and durability for the recycled aggregate concretes. Moreover, the strength of the concrete developed from mixed recycled aggregate was comparable with that of the reference concretes. Considering the low strength requirements for the construction of the lower layers of rigid pavements, it was established that such an application of recycled aggregate concrete, including that derived from mixed recycled aggregate, could be permitted.

Construction Materials doi: 10.3390/constrmater6020023

Authors: Nura Shehu Aliyu Yaro Jacob Adedayo Adedeji Zesizwe Ngubane Jacob Olumuyiwa Ikotun

Palm oil waste (POW) is generated during the production of palm oil, and a large quantity of this waste often travels to landfills for disposal. This review aims to provide a comprehensive understanding of the circular economy approach to sustainable engineering and environmental applications of POW, including its generation, disposal concerns, challenges, and prospects. This review provides an overview of the features, composition, and prospective applications of several POWs, including palm oil clinkers (POCs), palm oil fuel ashes (POFAs), palm oil kernel shells (POKSs), and palm oil fibres (POFs). Furthermore, this overview describes the different applications that POW has found, such as sustainable construction materials, renewable energy production, and environmental remediation. Moreover, this review discusses the leaching and risk assessment of POW. The overview also discusses the circular economy implications of using POW. The results showed that while some wastes are reused and recycled, a good quantity are still discarded in environmentally harmful ways. With this overview of a wide circular economy approach to the sustainable use of POW, there will be a rallying call to experts and researchers to identify research gaps that could contribute to the sustainable use of POW. The results of this overview of the sustainable engineering and environmental applications of POW with a circular economy approach indicate that cleaner production technologies and better environmental sustainability of the palm oil industry are feasible through proper waste management, renewable energy generation, resulting in minimal environmental impacts. Furthermore, this analysis will be very useful in providing tools to engineers, environmentalists, and other relevant stakeholders to enable the efficient and sustainable use of POW in the global circular economy.

Construction Materials doi: 10.3390/constrmater6020022

Authors: Demewoz W. Menna Aikaterini S. Genikomsou

This study investigates the pullout behaviour of hooked-end superelastic shape memory alloy (SMA) fibres embedded in concrete with the aim to develop an analytical model. Single fibre pullout experiments were performed to evaluate the mechanical response of SMA fibres with various hook geometries. A mathematical model based on the friction pulley method was then developed to predict the experimental pullout load versus displacement plots. The model integrates the tensile stress–strain response and the elastic–plastic constitutive behaviour of superelastic SMA materials, while also accounting for fibre slip and superelastic deformation during the pullout process. The pullout process is modelled through staged mechanisms including elastic response and debonding, progressive mechanical anchorage, and frictional pullout. The contribution of mechanical anchorage is governed by the elastic–superelastic strain distribution within the hook bends. The proposed model reasonably reproduces the overall load-slip response, peak pullout load, slip at peak load, and pullout energy for the three different fibre geometries extracted from normal strength and high-performance concrete matrix. The proposed mathematical model offers a transferable and predictive tool for assessing the pullout performance of hooked-end SMA fibres and supports their integration into design of SMA fibre-reinforced cementitious composites.

Construction Materials doi: 10.3390/constrmater6020021

Authors: Mu’tasim Abdel-Jaber Mousa Shhabat Ahmed Ashteyat Ahmad Al-Khreisat Omar Shehabat

The depletion of natural aggregates and the rapid increase in construction and demolition waste have intensified the need for sustainable structural materials. Recycled aggregates (RAs) represent a promising alternative; however, their performance under elevated temperatures remains insufficiently investigated. This study examines the combined influence of recycled coarse and fine aggregates (RCFA) replacement ratios and fire exposure on the shear behavior of RC beams. Five replacement levels (0%, 25%, 50%, 75%, and 100%) were considered. A total of forty-five beams (1500 × 150 × 200 mm) were tested at 23 °C, 400 °C, and 600 °C. In addition, a finite element model was developed to validate the experimental findings. The results showed at 23 °C, increasing the RA content led to a moderate reduction in the ultimate shear capacity of approximately 6–10%. Fire exposure significantly aggravated strength degradation, with additional reductions of up to 11% at 400 °C and total losses reaching about 22% at 600 °C compared to the control beam at room temperature. Stiffness deterioration and crack propagation became more pronounced with higher temperatures and replacement ratios due to thermal damage to the cement matrix and interfacial transition zones. Nevertheless, moderate replacement levels (25–50%) maintained acceptable residual shear capacity and improved ductility and energy absorption. Numerical predictions closely matched experimental results, with load differences within 1–5%, confirming the model’s reliability.

Construction Materials doi: 10.3390/constrmater6020020

Authors: Tai-Yi Liu Jui-Jiun Lin Shih-Ping Ho Nelson N. S. Chou Chia-Cheng Lee

Construction materials are the primary source of embodied carbon in long-span bridge projects, particularly for steel-intensive structures. This study presents an empirical construction-stage carbon footprint assessment of the Anhsin Bridge, an asymmetric cable-stayed steel truss bridge in Taiwan. Using the emission factor method in accordance with ISO 14067 and Taiwan Environmental Protection Administration guidelines, a cradle-to-gate (A1–A5 equivalent) system boundary was applied, covering material production, transportation, and on-site construction activities. Total construction-stage emissions were estimated at 55,349 tCO2e, dominated by structural steel (51.8%), followed by reinforcing steel, concrete, and cement. Material-related emissions accounted for over 90% of the total, highlighting the critical role of material selection in embodied carbon reduction. Three practical mitigation strategies were evaluated using verified project data, as follows: 40% cement substitution with supplementary cementitious materials, optimized steel erection methods, and enhanced reuse of formwork and temporary works. The combined scenario achieved a 7.3% reduction in construction-stage emissions without compromising constructability. The findings demonstrate the effectiveness of material-oriented, constructability-aware strategies for reducing embodied carbon in steel-intensive bridge construction.

Construction Materials doi: 10.3390/constrmater6020019

Authors: Abdurasul Martazaev Sobirjon Razzakov

Fiber-reinforced concrete has proved to be viable in improving the mechanical characteristics of structural elements to the flexural and shear stresses. The concrete cubes, prisms, and cylinders were standardized, cast and cured after 28 days to assess the baseline mechanical characteristics. Beam specimens were made of different types of fibers, lengths, and different volumetric contents and then subjected to controlled shear tests in which the crack initiation, propagation, and deformation were accurately measured. The experimental data proved that the addition of fibers was highly beneficial in terms of the mechanical performance of concrete. Basalt fibers enhanced compressive strength by up to 20.8 percent and tensile strength by 30.8 percent, whereas steel fibers had the best flexural strength with a maximum compressive and bending strength of 47.2 MPa and 6.56 MPa, respectively, at optimum dosage. Polypropylene fibers also improved performance, but in a lesser manner. The fiber addition served well to reduce the width of cracks and retard crack propagation, thus enhancing load-bearing capacity. These results show that dispersed fiber reinforcement that uses steel and basalt fibers is a practical solution to improving the dispersion of concrete in terms of durability and load-bearing capacity. The research will help guide the selection of fiber and the content in the reinforced concrete work to offer more robust and sustainable solutions to building.

Construction Materials doi: 10.3390/constrmater6020018

Authors: Il-Sang Ahn Lijuan Cheng

Tire-Derived Aggregate (TDA) is a recycled fill material made by cutting scrap tires into small pieces that satisfy the gradation requirements in ASTM D 6270. Since its introduction to civil engineering applications, TDA fill and TDA backfill have been successfully implemented in many projects. However, the dynamic behavior of the TDA backfill under significant earthquakes has not been substantially addressed. The present study used nonlinear time-history Finite Element Analysis (FEA) to analyze the dynamic behavior of a retaining wall with TDA backfill captured from the full-scale shake table test. Unlike typical soil failure observed in a similar retaining wall with conventional soil backfill, significant wall sliding occurred because lightweight TDA contributed to reducing the friction resistance of the wall footing. Therefore, the analysis required modeling capability of rigid body motion and impact loading from the separation between the wall stem and the backfill. With adequate friction models and softened contact models, the FEA generated the dynamic motion of the retaining wall that matched well with the measured responses, including the wall sliding. The friction model between the wall footing and soil was most critical in accurately reproducing wall sliding motion. It was determined to use different friction coefficients for the two different earthquakes used in the study in order to simplify the rate dependence of the coefficient. Also, the softened contact model generated more reasonable impact force by allowing overclosure and finite stiffness during impact. The FEA model and modeling technique in the present study can be used for the seismic design of various field-scale retaining walls with TDA backfill.

Construction Materials doi: 10.3390/constrmater6020017

Authors: Andrea Serpi James Rombi Gustavo Boada-Parra Francesca Maltinti Mauro Coni

In recent decades, the need to embrace the concepts of the circular economy and ecological transition has become increasingly apparent, especially in the civil engineering sector. This research aims to study a Cement-Bound Granular Material (CBGM) pavement layer using the industrial by-product Anhydrous Calcium Sulphate (ACS) as a partial replacement for Portland Cement (PC) by weight. The dual objective is to reduce environmental impact and ensure long-term high mechanical performance. Mechanical tests conducted at different curing periods (7, 28, 96, and 120 days) showed compressive strength gains of up to 180%. The evolution of the mechanical behavior was correlated with the formation of the gypsum dihydrate and ettringite hydrated phases, found by quantitative XRD analysis, to reinforce the cement matrix. Finite element simulations and fatigue life predictions using Miner’s rule over pavement lifespans of 15, 20, and 30 years indicated an increase in durability by a factor of 4.68 for the ACS-enhanced mixture compared to traditional PC-only formulations. Leaching tests show the material performs within acceptable environmental thresholds, even if its classification and acceptance may differ across regulatory systems, suggesting a solid basis for its application in sustainable practices.

Construction Materials doi: 10.3390/constrmater6020016

Authors: Gabriela Peñafiel Carlos Navarro Santiago Medina Robalino Fernanda Pico Bernarda Abril Byron Quishpe Luis Felipe Contreras-Vásquez

Concrete remains one of the most widely utilized construction materials, valued particularly for its exceptional compressive strength. However, exposure to fire can compromise both its internal microstructure and external integrity. This research investigates the behavior of concrete manufactured with recycled concrete coarse aggregate (RCA) derived from construction waste, aiming to establish experimental evidence of fire’s impact on compressive strength. We employed the Optimal Density Method to design mix proportions targeting 24 MPa compressive strength. The experimental program comprised 45 cylindrical samples distributed across three replacement levels: 0%, 15%, and 30% natural aggregate substitution with RCA. Following 28 days of curing, samples underwent direct fire exposure in a melting furnace. Temperature progression was monitored using a pyrometer, ranging from ambient (0 °C) through 250 °C, 400 °C, 600 °C, to 800 °C, with controlled exposure duration at each level. Three samples were tested at each temperature. After fire exposure, samples were cooled for 24 h at ambient temperature before compression testing. The densities of the fresh specimens were determined to be 2254.06 kg/m3 for HS-0AR%, 2210.09 kg/m3 for HS-15AR%, and 2180.85 kg/m3 for HS-30AR%, with a percentage density variation with respect to HS-0AR% of 1.95% and 3.25%, respectively. Finally, in relation to the compressive strength of concrete, a reduction of 4.34% was observed for 15% AGR and 5.72% for 30%, suggesting that the variations may be due to factors such as the water/cement ratio, the quality of the aggregate, and the curing conditions of concrete. In addition, several pathologies were observed, such as cracking, fissures, color changes, and spalling.

Construction Materials doi: 10.3390/constrmater6020015

Authors: Mohammad Al-Zu’bi Mazen J. Al-Kheetan Musab Rabi

The ongoing concern about sustainable infrastructure has driven the development of cement-based adhesives (CBAs) for fibre-reinforced polymer (FRP)-based concrete retrofitting. Nevertheless, traditional CBAs usually have low bond strength, low crack resistance, and low long-term durability that undermine the performance of FRP–concrete systems. To address these limitations, this focused review examines the potential of nanomaterial-modified CBAs to enhance interfacial bond behaviour and overall structural performance. A systematic assessment of recent experimental studies was used to analyze CBAs modified with nanosilica, carbon nanotubes, graphene oxide, and other nanomaterials. The roles of these nanomaterials in improving adhesion mechanisms, stress transfer efficiency, crack control, and resistance to environmental stressors are critically discussed. We also contrast the performance of neat and nano-modified CBAs in FRP-based retrofitting systems, with particular emphasis on bond behaviour, mechanical response, and durability-related performance. Particular emphasis is put on innovative high-strength self-compacting cementitious adhesives (IHSSC-CAs), which are identified as an emerging class of sustainable bonding materials combining high mechanical performance with improved environmental compatibility in relation to traditional bonding systems. The paper concludes with the identification of key research gaps, a discussion of practical implementation challenges, and an outline of future research directions for the development of next-generation sustainable and resilient concrete retrofitting technologies.

Construction Materials doi: 10.3390/constrmater6010014

Authors: Daniyar Akhmetov Aleksej Aniskin Baitak Apshikur Aizhan Baikunirova

This study assessed whether electrochemical activation of mixing water can enhance autoclaved aerated concrete (AAC), in which fly ash replaces sand as the siliceous component. Mixing water was electrolyzed in a diaphragm-type “Melesta” unit to obtain the catholyte and anolyte, and fly ash was pre-exposed to the catholyte for up to 15 min. The material’s behavior was evaluated using slurry flow tests, scanning electron microscopy, Fourier-transform infrared spectroscopy, macropore-uniformity analysis, mercury intrusion porosimetry, and shrinkage and short-term durability indicators. At an approximately constant density class near 600 kg/m3, the catholyte-pretreated fly-ash AAC mixes showed a near-monotonic increase in compressive strength with increasing fly-ash replacement (relative to the sand-based reference), while fresh-mixture fluidity decreased. The pore structure became more uniform, as indicated by a decrease in the standard deviation of pore diameters from 0.175 to 0.133 mm, and porosimetry indicated a higher micro-porosity fraction in fly-ash AAC than in sand-based AAC. Capillary shrinkage remained essentially unchanged, and short-term durability indicators (durability coefficients after 25 cycles) showed a small improvement. Overall, electrochemically activated water promoted a more regular pore system and stronger interpore walls under autoclave curing, supporting higher fly-ash utilization without loss of dimensional stability. The results are limited to one fly-ash source (Ekibastuz TPP); transferability should be verified using ashes with different glass content, fineness, and carbon/LOI.

Construction Materials doi: 10.3390/constrmater6010013

Authors: Rute Eires Raphaele Malheiro Thianne Peixoto Arlen Zúniga

Lime kiln dust (LKD), a by-product of the paper industry, generates about 100 tonnes of waste per 400,000 tonnes of kraft paper produced, while global aquaculture yields more than 16 million tonnes of oysters annually, 65–90% of which is made up of shells. This study explores their valorisation in the production of more eco-friendly mortars by partially replacing hydrated lime with LKD and oyster shell powder (OSP). In addition, a vinegar solution (VS), prepared by reacting oyster shells with white vinegar (~5% acetic acid), was used as an alternative mixing liquid instead of water. The LKD and OSP were tested at different substitution levels, showing promising mechanical performance, supporting their use as sustainable alternatives in mortar production. Replacement levels of 25%, 50% and 90% achieved compressive strengths ≥ 0.4 MPa at 28 days. At 28 days, the reference lime mortar prepared with water reached 0.83 MPa, while the use of the vinegar solution increased the compressive strength to 1.86 MPa, representing an improvement of approximately 124%. Regarding binder replacement by wastes, the most efficient mechanical performance was obtained for mixtures with 50% LKD substitution, reaching 2.04 MPa at 28 days and 3.11 MPa at 60 days, increasing by 10% and 43%, respectively, while mixtures incorporating oyster shell powder showed more stable mechanical behaviour across substitution levels. Using a hot-mixing process with quicklime in the presence of the vinegar-based solution and sand may account for the higher strengths, due to the heat/steam generated during lime hydration prior to moulding and verified by microscopy. In addition, VS-containing mixes showed higher aragonite contents and detectable phosphorus-bearing compounds, which may further contribute to matrix densification and strengthening. Overall, the results indicate that the combined use of uncalcined calcium-based wastes and a vinegar-based solution can contribute to the development of calcium-based mortars with good mechanical performance, supporting circular economy strategies and the reduction in calcined-binder use in construction materials.

Construction Materials doi: 10.3390/constrmater6010012

Authors: Rajeev Devaraj Ayodele Olofinjana Christophe Gerber

Glass fibre-reinforced polymer (GFRP) offers a durable, high-tensile strength alternative to steel rebar in reinforced concrete (RC). However, the inherent lack of ductility in GFRP limits its structural applications, which has led to the development of hybrid GFRP–steel RC systems. The composite nature of these systems requires an accurate understanding of the bond interaction between GFRP rebar and concrete. Existing bond models often fall short of accurately representing the distinct mechanical properties and surface characteristics of GFRP bars, particularly within finite element (FE) analysis environments. To address this gap, the present study proposes a computational method that employs a feedforward neural network (FFNN) trained on experimental data encompassing a specific range of parameters (bar diameters 8–16 mm, concrete strengths 18–50 MPa), including bar diameter, bond length, concrete strength, and cover thickness. Unlike conventional models that typically focus on peak bond strength, the developed FFNN accurately predicts the complete bond–slip relationship. The developed bond model is then integrated into the FE analysis. The simulation results demonstrate strong agreement with experimental data (average R2 = 0.93) and effectively capture key behavioral aspects such as crack initiation and propagation.

Construction Materials doi: 10.3390/constrmater6010011

Authors: Enea Mustafaraj Erion Luga Christina El Sawda Elio Ziade Khaled Younes

Accurate prediction of the mechanical performance of fiber-reinforced cement mortars (FRCM) is challenging because fiber geometry and properties vary widely and interact with the cement matrix in a non-trivial way. In this study, we propose an interpretable, computationally light framework that combines principal component analysis (PCA) with multiple linear regression (MLR) to predict compressive strength (Cs) and flexural strength (Fs) from mix proportions and fiber parameters. The literature-based dataset of 52 mortar mixes reinforced with polypropylene, steel, coconut, date palm, and hemp fibers was compiled and analyzed, covering Cs = 4.4–78.6 MPa and Fs = 0.75–16.7 MPa, with fiber volume fraction Vf = 0–15% and fiber length Fl = 4.48–60 mm. PCA performed on the full dataset showed that PC1–PC2 explain 53.4% of the total variance; a targeted variable-selection strategy increased the captured variance to 73.0% for the subset used for regression model development. MLR models built using PC1 and PC2 achieved good accuracy in the low-to-mid strength range, while prediction errors increased for higher-strength mixes (approximately Cs ≳ 60 MPa and Fs ≳ 10 MPa). On an independent validation dataset (n = 10), the refined model achieved mean absolute percentage errors of 11.3% for Fs and 18.5% for Cs. The proposed PCA-MLR approach provides a transparent alternative to more complex data-driven predictors, and it can support preliminary screening and optimization of fiber-reinforced mortar designs for durable structural and repair applications.

Construction Materials doi: 10.3390/constrmater6010010

Authors: Van Nam Pham Toshihiro Sakaki Ken Kawamoto

Thermal properties, such as thermal conductivity (λ) and heat capacity (Cv), are important in understanding heat transport and the urban heat island (UHI) effect. While many studies focus on surface materials rather than roadbed materials, this study targeted roadbed materials using recycled concrete aggregates mixed with autoclaved aerated concrete (AAC) grains to experimentally measure and to predict the λ and Cv under varied moisture conditions. The results showed that both λ and Cv of all tested samples increased linearly with increasing volumetric water content (θ), and the increment of AAC was effective in reducing the λ values in the whole range of θ. The addition of AAC, on the other hand, did not affect the measured Cv significantly and gave a linear increase in Cv with the increase in θ. The performance of predictive models showed that Archie’s-second-law-based model captured the measured λ values for all tested samples well by modifying the saturation exponent (n = 0.7), and the classic de Vries model predicted the measured Cv well, suggesting that Archie’s-second-law-based model would be useful to evaluate heat transport parameters for roadbed materials in this study.

Construction Materials doi: 10.3390/constrmater6010009

Authors: Mikhailo Brykov Vasyl’ Girzhon Volodymyr Lebedev Ruslan Kulykovskyi Oleksii Kapustyan Olexandr Klymov Alexey Efremenko Denys Molochkov

Samples of medium-carbon low alloyed steel (0.45 wt% C, 2.61 wt% Mn, 1.57 wt% Si) with bainite microstructure were welded using the cold metal transfer method. A series of single welding “dots” was made to produce welding joints using austenitic welding wires. The heat input was adjusted to the minimal possible level of 500–800 J per “dot”. Tensile tests of welded samples demonstrated that quality welds were obtained. All samples were broken via welded metal, showing tensile strength 530–670 MPa, which is inherent to the material of the welding wires. It was determined that the time required for phase transformations in the heat-affected zone during the thermal cycle is an order of magnitude greater than the time of temperature flash during producing a single welding “dot”. The results of extensive hardness measurements of material in the heat-affected zone, along with macro- and microstructure investigations, are presented. It has been demonstrated that cold metal transfer welding technology can be successfully used for welding steel with high carbon equivalent and bainite microstructure without preheating and with minimal deterioration of properties in the heat-affected zone.

Construction Materials doi: 10.3390/constrmater6010008

Authors: Rodrigo H. Geraldo Jardel P. Gonçalves Gladis Camarini

Recent studies have highlighted the potential for production of an alternative sodium silicate in powder obtained by mixing NaOH with rice husk ash, followed by a dissolution and drying process. This alternative sodium silicate, when mixed with metakaolin and dried under special conditions, results in an eco-friendly one-part alkali-activated binder (OPAAB). However, the durability performance of OPAAB incorporating RHA-derived sodium silicate remains largely unexplored. This study focuses on an experimental investigation of OPAAB mortar durability, analyzing permeability, high-temperature exposure, wet-and-dry cycles, and resistance to aggressive environments (sulfate and acid attack). A two-part mix mortar made with the same precursors was used as a reference. It was found that the OPAAB mortars were not affected by the wet-and-dry cycles nor the sulfate attack. Exposure to high temperature (900 °C for 1 h) did not cause specimen failure, which had a residual compressive strength higher than 5 MPa. Finally, exposure to sulfuric acid for 56 days decreased the mechanical strength of the mortars, but all the specimens maintained a residual compressive strength higher than 4 MPa. The durability performance of the mortars produced with OPAAB incorporating RHA-derived sodium silicate was similar to the two-part mix mortars (reference), demonstrating technical feasibility and advancing the understanding of durability aspects for application in civil construction.

Construction Materials doi: 10.3390/constrmater6010007

Authors: Oscar Graos-Alva Aldo Castillo-Chung Marisol Contreras-Quiñones Alexander Vega-Anticona

Geopolymer mortars were produced from construction and demolition waste using a binary binder of recycled brick powder/recycled concrete powder (RBP/RCP = 70/30 wt%), activated with a hybrid alkaline solution (NaOH/Na2SiO3/KOH) and reinforced with sisal fibres at 0–2 wt%. Mechanical performance (compression and three-point bending) and microstructure–phase evolution (XRD, FTIR, SEM-EDS) were assessed after low-temperature curing. Sisal addition delivered a strength–toughness trade-off with a reproducible optimum at ~1.0–1.5 wt%; at 2.0 wt%, fibre clustering and connected porosity reduced the effective load-bearing section, penalising flexure more than compression. Microstructural evidence indicates coexistence and co-crosslinking of N-A-S-H and C-(A)-S-H gels—enabled by Ca from RCP—leading to matrix densification and improved fibre–matrix anchorage. Fractographic features (tortuous crack paths, bridging, and extensive pull-out at ~1.5 wt%) are consistent with an extended post-peak response and higher fracture work without compromising early-age strength. This study achieves the following: (i) it identifies a practical reinforcement window for sisal in RBP/RCP geopolymers, (ii) it links gel chemistry and interfacial phenomena to macroscopic behaviour, and (iii) it distils processing guidelines (gradual addition, workability control, gentle deaeration, and constant A/S) that support reproducibility. These outcomes provide a replicable, low-embodied-CO2 route to fibre-reinforced geopolymer mortars derived from CDW for non-structural and semi-structural applications where flexural performance and post-peak behaviour are critical.

Construction Materials doi: 10.3390/constrmater6010006

Authors: Ali Juma Alnaqbi Waleed Zeiada Ghazi G. Al-Khateeb

Road safety and maintenance strategy optimization depend on accurate pavement surface friction prediction. In order to predict the Friction Number for Continuously Reinforced Concrete Pavement (CRCP) sections using data taken from the Long-Term Pavement Performance (LTPP) database, this study presents a hybrid machine learning framework that combines Gradient Boosting Machines (GBMs) with Genetic Algorithm (GA) optimization. Twenty input variables from the structural, climatic, traffic, and performance categories were used in the analysis of 395 data points from 33 CRCP sections. With a mean Root Mean Squared Error (RMSE) of 3.644 and a mean R-squared (R2) value of 0.830, the GA-optimized GBM model outperformed baseline models such as non-optimized GBM, Linear Regression, Random Forest, Support Vector Regression (SVR), and Artificial Neural Networks (ANN). The most significant predictors, according to sensitivity analysis, were AADT, Total Thickness, Freeze Index, and Pavement Age. The marginal effects of these variables on the expected friction levels were illustrated using partial dependence plots (PDPs). The results show that the suggested GA-GBM model offers a strong and comprehensible instrument for forecasting pavement friction, with substantial potential for improving safety evaluations and maintenance scheduling in networks of rigid pavement.

Construction Materials doi: 10.3390/constrmater6010005

Authors: Amr El Ragaby Jehad Alkatan Faouzi Ghrib Mofrhe Alruwaili

In accelerated bridge construction, precast concrete girders are connected to cast-in-place concrete slab using shear transfer reinforcement across the interface plane to ensure the composite action. The steel transverse reinforcement is prone to severe corrosion due to the extensive use of de-icing salts and severe environmental conditions. As glass fiber-reinforced polymer (GFRP) reinforcement has shown to be an effective alternative to conventional steel rebars as flexural and shear reinforcement, the present research work is exploring the performance of GFRP reinforcements as shear transfer reinforcement between precast and cast-in-place concretes. Experimental testing was carried out on forty large-scale push-off specimens. Each specimen consists of two L-shaped concrete blocks cast at different times, cold joints, where GFRP reinforcement was used as shear friction reinforcement across the interface with no special treatment applied to the concrete surface at the interface. The investigated parameters included the GFRP reinforcement shape (stirrups and headed bars), reinforcement ratio, axial stiffness, and the concrete compressive strength. The relative slip, reinforcement strain, ultimate strength, and failure modes were reported. The test results showed the effectiveness and competitive shear transfer performance of GFRP compared to steel rebars. A shear friction model for predicting the shear capacity of as-cast, cold concrete joints reinforced by GFRP reinforcement is introduced.

Construction Materials doi: 10.3390/constrmater6010004

Authors: Bahruddin Ibrahim Zuchra Helwani Jahrizal Nasruddin Arya Wiranata Edi Kurniawan Anjar Siti Mashitoh

One of the main obstacles to producing natural rubber-modified asphalt is the difficulty of mixing Technical Specification Natural Rubber (TSNR) or its compounds with asphalt, leading to long mixing times and high costs. This study aims to evaluate the use of 60/70 penetration asphalt as a plasticizer to accelerate the mixing process and improve the rheological properties of modified asphalt using Technical Specification Natural Rubber (TSNR). The production process for technical specification natural rubber-modified asphalt involves two stages: the production of the technical specification natural rubber compound (CTSNR) and the production of CTSNR-based modified asphalt (CTSNRMA). The CTSNR production process begins with mastication of technical specification natural rubber (TSNR), followed by the addition of activators (zinc oxide, stearic acid), accelerators (Mercaptobenzothiazole sulfenamide (MBTS)), antioxidants (2,2,4-Trimethyl-1,2-dihydroquinoline (TMQ)), and 60/70 penetration asphalt as a plasticizer (at concentrations of 30%, 40%, and 50%). After homogeneous mixing for 30–60 min, the CTSNR is diluted 5–10 mm for the next mixing stage with hot asphalt at 160–170 °C. The best results of this study showed that CTSNR-modified asphalt with 4% rubber content and 50% plasticizer (CTSNRM-450) successfully reduced the mixing time to 16 min, making it more efficient than the traditional method, which takes up to 180 min. The addition of asphalt plasticizer decreased penetration to 35.6 dmm and increased the softening point to 55.4 °C. The CTSNRMA-440 formula, with 4% rubber content and 40% plasticizer, produced the best results in terms of storage stability, meeting the ASTM D5892 standard with a softening-point difference of 0.95 °C, which is well below the threshold of 2.2 °C. The CTSNRMA-440 sample achieved a Performance Grade (PG) of 76, suitable for hot-climate conditions, with a significant reduction in mixing time, greater stability, and increased resistance to high temperatures.

Construction Materials doi: 10.3390/constrmater6010003

Authors: Dulat Abdrassilov Aleksej Aniskin Zhanbolat Shakhmov Rauan Lukpanov

The construction industry relies on building materials that provide not only high physical and mechanical performance but also adequate thermal and durability properties. However, several factors still limit the quality and service life of concrete products. The development of the construction industry provides new opportunities for designing efficient construction facilities. To obtain enhanced design capabilities, it is very important to relieve the load on the structure, this can be achieved by reducing the mass of materials without losing strength. This study investigates the enhancement of foam concrete through the combined incorporation of mineral fibers recycled from basalt insulation waste and complex polymer modifiers. The aim was to improve the material’s mechanical performance, durability, and pore structure stability while promoting the sustainable use of industrial by-products. The experimental program included tests on density, compressive strength, water absorption, and thermal conductivity for mixtures of different densities (400–1100 kg/m3). The results demonstrated that the inclusion of mineral fibers and polymer modifiers significantly enhanced structural uniformity and pore wall integrity. Compressive strength increased by up to 35%, water absorption decreased by 25%, and thermal conductivity was reduced by 18% compared with the control mixture.

Construction Materials doi: 10.3390/constrmater6010002

Authors: Vitalii Kryzhanovskyi Sergii Kroviakov Pavlo Shymchenko Inna Aksyonova

Driving the circular economy in road construction requires the effective use of secondary materials like recycled concrete aggregate (RCA) and fly ash (FA). A key obstacle is the performance trade-off in concretes incorporating both materials. This research investigates feasible mix designs for road concrete, using RCA as a full gravel replacement and FA as a cement substitute. Polypropylene fiber (36 mm) and a superplasticizer were utilized to mitigate fresh and hardened state drawbacks. The experimental program included 15 modified mixtures with recycled aggregate and 3 control mixtures with natural aggregate. The workability of all concrete mixtures was kept constant at slump class S1. Road concretes with RCA, containing a 10–12% FA by cement replacement, at least 2 kg/m3 of polypropylene fiber (PF), and 4 kg/m3 of superplasticizer (SP), achieve compressive strength of at least 50 MPa and flexural strength of no less than 5 MPa at the design age. This performance is comparable to that of control mixtures. Furthermore, the abrasion resistance ranges between 0.48–0.50 g/cm2, and the brittleness index falls within 0.095–0.100, significantly enhancing the durability of concrete for rigid pavement applications. The conducted cradle-to-gate life-cycle assessment (stages A1–A3) of the constituent materials for 1 m3 of concrete indicates the following environmental impacts: Global Warming Potential (GWP) of 195 kg CO2 equation, Non-renewable Primary Energy Demand (PENRE) of 1140 MJ, Abiotic Depletion Potential for Fossil resources (ADPF) of 1120 MJ, Acidification Potential (AP) of 0.45 mol H+ equation, and Eutrophication Potential (EP) of 0.07 kg PO43− equation It is established that the modified compositions not only meet the required performance criteria but also contribute to the goals of resource conservation in road construction.

Construction Materials doi: 10.3390/constrmater6010001

Authors: John Audu Sylvester Osuji Okiemute Ogirigbo

The Otukpo Burnt Brick Factory has remained dormant for more than three decades despite repeated government interventions. In this context, the present study investigates the suitability of soils from Otukpo, Benue State, Nigeria, for unfired brick production and as supplementary cementitious materials (SCMs). Four representative samples (OT1–OT4) were subjected to X-ray fluorescence (XRF), thermogravimetric analysis (TGA), particle size distribution (PSD), X-ray diffraction (XRD), unconfined compressive strength (UCS), cube strength, shrinkage, and water absorption tests. The results revealed high reactive oxide contents (SiO2 + Al2O3 + Fe2O3 > 93%) with low SO3 and moderate loss on ignition (~6%), thus indicating strong pozzolanic potential. PSD residues on the 45 µm sieve ranged from 6.8 to 17%, which is well below the ASTM C618 limit of 34%. XRD confirmed quartz and kaolinite as dominant phases. Strength activity indices showed that only OT3 and OT4 exceeded Nigerian (NIS 693:2007) and Indian (IS 1725:2023) standards when stabilized with 5 wt.% cement or sodium hydroxide; while OT1 and OT2 were below these thresholds. Water absorption values for OT3 (18.69%) and OT4 (19.04%) marginally satisfied Indian standards but failed Nigerian requirements, which is reflective of high porosity. Linear shrinkage (~14%) met IS 1498 marginally, and pH values (6.14–6.34) were consistent with lateritic soils. Overall, OT3 and OT4 demonstrated promise for low-energy SCMs and unfired brick applications, though they must be restricted to non-load-bearing uses unless further stabilization is applied.

Construction Materials doi: 10.3390/constrmater5040092

Authors: Lukas Steffen Ismael Viejo Belén Hernández-Gascón Mario Stelzmann Klaus Holschemacher Robert Böhm

Textile-reinforced concrete (TRC) sandwich panels with lightweight cores are a promising solution for sustainable and slender building envelopes. However, their structural performance depends strongly on the shear connection between the outer shells. This study investigates the flexural behavior of TRC sandwich panels with glass fiber-reinforced polymer (GFRP) rod connectors under four-point bending. Three full-scale specimens were manufactured with high-performance concrete (HPC) face layers, an expanded polystyrene (EPS) core, and 12 mm GFRP rods as shear connectors. The panels were tested up to failure, with measurements of load–deflection behavior, crack development, and interlayer slip. Additionally, a linear-elastic finite element model was developed to complement the experimental campaign, capturing the global stiffness of the system and providing complementary insight into the internal stress distribution. The experimental results revealed stable load-bearing behavior with ductile post-cracking response. A degree of composite interaction of γ = 0.33 was obtained, indicating partially composite action. Slip measurements confirmed effective shear transfer by the GFRP connectors, while no brittle failure or connector rupture was observed. The numerical analysis confirmed the elastic response observed in the tests and highlighted the key role of the GFRP connectors in coupling the TRC shells, extending the interpretation beyond experimental results. Overall, the study demonstrates the potential of TRC sandwich panels with mechanical connectors as a safe and reliable structural solution.

Construction Materials doi: 10.3390/constrmater5040091

Authors: Nurshafarina Jasme Kim Hung Mo Farid Wajdi Akashah Chee Ban Cheah

The development of sustainable self-compacting concrete (SCC) requires alternative binders that minimise ordinary Portland cement (OPC) consumption while ensuring long-term performance. This study investigates sulfate-activated SCC (SA SCC) incorporating high volumes of industrial by-products, whereby 72% ground granulated blast furnace slag (GGBS) and 18% fly ash (FA) were activated with varying proportions of OPC and gypsum. Quarry dust was used as a fine aggregate, while granite and electric arc furnace (EAF) slag served as coarse aggregates. Among all formulations, the binder containing 72% GGBS, 18% FA, 4% OPC, and 6% gypsum was identified as the optimum composition, providing superior mechanical performance across all curing durations. This mix achieved slump flow within the EFNARC SF2 class (700–725 mm), compressive strength exceeding 50 MPa at 270 days, and flexural strength up to 20% higher than OPC SCC. Drying shrinkage values remained below Eurocode 2 and ASTM C157 limits, while EAF slag increased density, but slightly worsened shrinkage compared to granite mixes. Microstructural analysis (SEM-EDX) confirmed that strength development was governed by discrete C-S-H and C-A-S-H gels surrounding unreacted binder particles, forming a dense interlocked matrix. The results demonstrate that sulfate activation with a 4% OPC + 6% gypsum blend enables the production of high-performance SCC with 94–98% industrial by-products, reducing OPC dependency and environmental impact. This work offers a practical pathway for low-carbon SCC.

Construction Materials doi: 10.3390/constrmater5040090

Authors: Yashovardhan Sharma Meghana Yeluri Srinivas Allena

Ultra-high-performance concrete (UHPC) delivers outstanding durability and strength but typically relies on high Portland cement content. This study evaluates a 20% cement replacement with limestone powder (LP) in UHPC and benchmarks performance under two curing regimes: moist curing (MC) and warm bath curing at 90 °C (WB). Metrics include workability, compressive and flexural behavior, shrinkage, freeze–thaw resistance, chloride transport (surface resistivity, RCPT), material cost, and embodied CO2. LP improved fresh behavior: flow increased by 14.3% in plain UHPC and 33% in fiber-reinforced UHPC (FR-UHPC). Compressive strengths remained in the UHPC range at 28–56 days (approximately 142–152 MPa with LP), with modest penalties versus 0%-LP controls (about 2–5% depending on age and curing). Under WB at 56 days, controls reached 154 MPa (plain) and 161 MPa (FR-UHPC), while LP mixes achieved 145.2 MPa (plain) and 152.0 MPa (FR-UHPC). Flexural performance was reduced with LP: for FR-UHPC, 28-day MOR under MC was reduced from 15.5 MPa to 12.7 MPa and under WB from 14.3 MPa to 10.3 MPa; toughness under MC was reduced from 74.4 J to 51.1 J. Durability indicators were maintained or improved despite these moderate strength reductions. After 300 rapid freeze–thaw cycles, all mixtures retained relative dynamic modulus near 100–103%, with negligible MOR losses in LP mixes (plain UHPC: −1.1% with LP versus −4.7% without; FR-UHPC: −3.7% versus −8.1%). Chloride transport resistance improved: at 56 days under MC, surface resistivity increased from 558 to 707 kΩ·cm in plain UHPC and from 252 to 444 kΩ·cm in FR-UHPC; RCPT for LP mixes was 139 C (MC) and 408 C (WB), about 14–23% lower than respective controls. Drying shrinkage was reduced by roughly 23% (plain) and 28% (FR-UHPC). Sustainability and cost outcomes were favorable: embodied CO2 was reduced by 18.8% (plain) and 15.5% (FR-UHPC), and material cost was reduced by about 4.5% and 2.0%, respectively. The main shortcomings are moderate reductions in compressive and flexural strength and toughness, particularly under WB curing, which should guide application-specific limits and design factors.

Construction Materials doi: 10.3390/constrmater5040089

Authors: Valentina Tomei Marina Serpe Ernesto Grande Maura Imbimbo

The construction sector is a significant contributor to resource consumption and environmental degradation due to energy-intensive processes. To reduce consumption, reuse-based design strategies could lead to structurally efficient and environmentally friendly solutions. However, effectively incorporating reused elements requires advanced design methods that allow for their rational disposition. This paper presents an innovative design approach based on a metaheuristic strategy developed through genetic algorithms for the design of minimum-weight gridshells using reusable components. The methodology is applied to a dome gridshell, tested under different stock and boundary conditions. An expedited greenhouse gas assessment is then carried out to evaluate the environmental benefits of the reuse-based solutions compared to solutions composed entirely of new elements. The results are presented in terms of geometry, disposition of reused and new members, weight, structural performance (buckling factor, demand to capacity ratio, displacements), and greenhouse gas emissions. The algorithm is able to find the minimum weight solution for all the considered stocks, and to account for the different governing design criteria characterizing fully and partially constrained gridshells. Furthermore, it can also be used to determine the characteristics that the stock of reused elements should possess in order to achieve more sustainable design solutions.

Construction Materials doi: 10.3390/constrmater5040088

Authors: Choudhury Gyanaranjan Samal Dipti Ranjan Biswal Sujit Kumar Pradhan Ajit Kumar Pasayat

Construction and demolition (C&D) waste remains a critical challenge in India due to accelerated urbanisation and material-intensive construction practices. This study integrates survey-based assessment with machine learning to identify key causes of C&D waste and recommend targeted minimization strategies. Data were collected from 116 professionals representing junior, middle, and senior management, spanning age groups from 20 to 60+ years, and working across building construction, consultancy, project management, roadworks, bridges, and industrial structures. The majority of respondents (57%) had 6–20 years of experience, ensuring representation from both operational and decision-making roles. The Relative Importance Index (RII) method was applied to rank waste causes and minimization techniques based on industry perceptions. To enhance robustness, Random Forest, Gradient Boosting, and Linear Regression models were tested, with Random Forest performing best (R2 = 0.62), providing insights into the relative importance of different strategies. Findings show that human skill and quality control are most critical in reducing waste across concrete, mortar, bricks, steel, and tiles, while proper planning is key for excavated soil and quality sourcing for wood. Recommended strategies include workforce training, strict quality checks, improved planning, and prefabrication. The integration of perception-based analysis with machine learning offers a comprehensive framework for minimising C&D waste, supporting cost reduction and sustainability in construction projects. The major limitation of this study is its reliance on self-reported survey data, which may be influenced by subjectivity and regional bias. Additionally, results may not fully generalize beyond the Indian construction context due to the sample size and sectoral skew. The absence of real-time site data and limited access to integrated waste management systems also restrict predictive accuracy of the machine learning models. Nevertheless, combining industry perception with robust data-driven techniques provides a valuable framework for supporting sustainable construction management.

Construction Materials doi: 10.3390/constrmater5040087

Authors: Le Thi Nhung Nguyen Hoang Truong Anh Khoa Phan Minh Phuong Thanh-Danh Nguyen

Corrosion of steel structures remains a persistent challenge in construction, particularly in coastal and industrial environments where chloride-induced degradation accelerates structural failure. This study presents an eco-friendly approach to improve the corrosion protection of the steel by incorporating Lawsonia inermis (henna) leaf extract into zinc–aluminum silicate coatings. The henna extract was added at varying concentrations (0–12 wt%) to evaluate its influence on structure, adhesion, and electrochemical performance of the coating. Physicochemical characterizations including FTIR, XRD, XRF, and SEM revealed that a 5 wt% addition optimized pigment dispersion, resulting in a denser and more homogeneous coating microstructure. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests after 35 days of immersion in 3.5 wt% NaCl solution demonstrated that this formulation achieved the highest impedance and polarization resistance, confirming enhanced corrosion resistance. The improvement was attributed to the dual action of the henna extract: (i) as a dispersant, promoting uniform Zn–Al pigment distribution and reducing porosity, and (ii) as a green corrosion inhibitor, forming an adsorbed protective film on the steel surface. This work highlights the potential of bio-derived additives to enhance the long-term durability of steel infrastructure and supports the development of sustainable protective materials for construction applications.

Construction Materials doi: 10.3390/constrmater5040086

Authors: Jesús E. Altamiranda-Ramos Luis Castillo-Suárez Jesús Redondo-Mosquera Joaquín Abellán-García

Reactive Powder Concrete (RPC) is widely recognized for its high strength and durability, yet its dependence on large amounts of Portland cement (PC) and silica fume (MS) raises environmental and economic concerns. This study explores the combined incorporation of milled electric arc furnace slag (MEAS) and calcium carbonate powder (CCP) as partial substitutes for cement and MS in RPC, employing a Central Composite Design (CCD) to optimize cement dosage, water-to-binder ratio, and polycarboxylate ether (PCE) content. Particle packing was guided by the Modified Andreasen–Andersen (MAA) model. The experimental program included 20 mixtures, evaluating rheological performance through slump flow and mechanical strength at 1, 7, 14, and 28 days. Incorporating MEAS (up to ≈20% of the binder) and CCP (≈15%) improved workability, with slump flow values reaching ≈285 mm compared to ≈230 mm for the baseline mixture. The optimal formulation achieved a 28-day compressive strength of ≈152 MPa, comparable to the reference RPC (≈138 MPa), while reducing cement consumption by ≈15% and MS by ≈50% relative to conventional dosages. Quadratic response surface models for slump flow and compressive strength at 1–28 days showed excellent goodness of fit (R2 = 0.90–0.98, adjusted R2 = 0.85–0.96; model F-tests p < 0.001), confirming the adequacy of the statistical optimization. Moreover, statistical analysis confirmed that cement dosage was the dominant factor for strength development (p < 0.05), while the interaction between cement content and water-to-binder ratio significantly influenced flowability. These results demonstrate the potential of MEAS and CCP to lower binder demand in RPC without compromising mechanical performance, advancing sustainable alternatives for ultra-high-performance concrete.

Construction Materials doi: 10.3390/constrmater5040085

Authors: Oleksandr Gilodo Andrii Arsirii Sergii Kroviakov Oleksandr Gimanov

Cross-beam glued-laminated timber (glulam) floor systems offer material efficiency but pose a complex design challenge due to three-dimensional (3D) load interactions, and systematic optimization guidelines are lacking. This study implements a parametric optimization framework using a three-factor Design of Experiments (DOE) approach (beam spacing ratio, height-to-span ratio, width-to-height ratio). A total of 27 full-factorial finite element models (FEMs) were simulated in Dlubal RFEM. A second-order response surface methodology (RSM) model was developed to predict the load utilization factor (Y) in accordance with Eurocode 5. The predictive model demonstrated high statistical accuracy (R2 > 0.98). A multi-criteria optimization using the Pareto frontier identified a balanced solution (x1 = 0.250, x2 = 0.042, x3 = 0.5) that achieved 97.4% load utilization (Y = 0.974). This optimal configuration reduces the required timber volume by approximately 10% compared with other efficient designs and by over 60% compared with inefficient (Y ≈ 0.5) but safe designs within the experimental space. The resulting regression model provides a validated engineering tool for designing materially efficient glulam floor systems, allowing designers to balance structural safety with material economy.

Construction Materials doi: 10.3390/constrmater5040084

Authors: Victor M. E. Lima Igor V. Fernandes Diego H. Alves Tiago M. S. Agra Danilo J. da C. Barbosa Eudes A. Rocha Antonio A. Melo Neto

The UPV technique has been widely employed to predict the hardened properties of Portland cement mixtures. This article assesses the hardened properties of alkali-activated blast furnace slag mortars by comparing UPV measurements with compressive strength and dry density and calculating the dynamic modulus of elasticity from UPV results. The mixtures were prepared varying the type of activator (sodium metasilicate and sodium silicate), the content of Na2O in the activators (3.0, 4.5, 6.0, and 7.5%), and the water/binder ratio. The results showed that exponential models showed medium and high determination coefficients (R2), which explained the correlation between UPV and hardened properties. It was observed a limitation on the measurements of UPV, which did not surpass 4.4 km/s, which made it difficult to predict compressive strength value above 50 MPa. The dynamic modulus of elasticity calculated from UPV showed reliable results, even varying the Poisson’s coefficient between 0.15 and 0.25. Lastly, it was also observed that a correlation between the content of C-S-H and UPV suggested that this technique can also be used to predict the evolution of the hydration products in alkali-activated slag mixtures.

Construction Materials doi: 10.3390/constrmater5040083

Authors: Muhammad Irfan Nuryanta Muhammad Afif Nurhary Hendrix Noviyanto Firmansyah Dicke Joshua Makbul Hajad Rahmat Doni Widodo Teguh Dwi Widodo Muhammad Kusni Ardi Wiranata Arif Kusumawanto Muhammad Akhsin Muflikhun

Clay 3D printing is an emerging field within additive manufacturing that presents significant opportunities for both structural and artistic applications. Driven by the increasing interest in this technology, there is a growing demand for optimized printing protocols tailored to clay, a readily available and versatile material. This study investigates the optimal processing parameters for kaolin clay composites and assesses the influence of clay-to-water ratios on the physical and mechanical properties of printed specimens. Experimental results demonstrate that higher clay content enhances the dimensional stability and structural integrity of printed components. The optimal formulation was determined to be 60% clay and 40% water, which produced the highest mechanical performance: the flexural strength of sintered specimens reached 1.3125 MPa and the compressive strength attained a maximum of 6.14 MPa. Shrinkage analysis indicated that specimens with greater water content experienced increased volumetric shrinkage, with reductions of up to 10% in linear dimensions and 14% in mass during drying and sintering. These findings highlight the critical relationship between material composition and final part performance in clay 3D printing and provide guidance for optimizing material formulations to enhance the mechanical robustness of printed clay composite structures for diverse applications.

Construction Materials doi: 10.3390/constrmater5040082

Authors: Ali Abbas Anjana Kudukkan

The present experimental study was set up to examine the use of waste seashells (ground to powder form) to replace cement partially and as a filler material in concrete. Two distinct particle size ranges of seashell powder were adopted based on their intended function: 63–125 micron particles are used as a filler to enhance packing density, and 0–63 micron particles are used as a cement replacement to improve reactivity. Four concrete mixes, including a control mix, were designed, with ground seashell powder used to replace cement, both as a filler replacing 15% of the cement and additionally as finer seashell powder replacing 0, 15, and 30% of cement (labelled S0F15, S15F15, and S30F15, respectively). The seashells’ chemical, physical, and mineralogical properties were characterised using particle size analysis through sieving, X-ray diffraction (XRD), Scanning Electron microscopy (SEM), and pH test methods. Furthermore, the fresh properties of concrete, such as initial and final setting time, were studied. The hardened seashell-based concrete was subjected to direct compressive strength, bulk density, and modulus of elasticity analysis. The results showed that the 28-day compressive strength of concrete with seashells was moderately reduced by nearly 25% compared to the control mix. In the case of modulus of elasticity, the reductions were about 5%, 7% and 13% for mixes S0F15, S15F15 and S30F15, respectively, compared to the control mix CM. Finally, the carbon emission from concrete with 15% and 30% seashell powder content as cement replacement (plus 15% cement replaced with the powder acting as a filler in both cases) resulted in a notably lower carbon emission of 250 and 212 kg CO2 e/m3, respectively, compared to the control mix, with a reduction of approximately 24%. This is a sizable reduction in Global Warming Potential (GWP) value. Therefore, the study concluded that the investigated seashell powder in concrete could benefit an eco-friendly environment and conservation of natural resources.

Construction Materials doi: 10.3390/constrmater5040081

Authors: Sarah Al-Qutaifi Rusul M. Rashid Atared Salah Kawoosh

Composite geopolymer concrete (CGPC), is receiving growing attention in the construction sector for its sustainable nature, environmental benefits, and its valuable role in promoting efficient waste utilization. The strategic incorporation of reinforcing fibers into geopolymer concrete (GPC) matrices is critical for enhancing mechanical performance and meeting the durability requirements of high-performance construction applications. Although substantial research has focused on strength enhancement of fiber-reinforced geopolymer concrete (FGPC) individually, it has neglected practical considerations such as energy use for curing and life-cycle assessments. Thus, this study investigates the cost-effective aspects of FGPC cured under different regimes. Different cementitious binders were incorporated, i.e., fly ash (FA) and ground granulated blast-furnace slag (GGBS), in addition to alkaline activators (a combination of sodium hydroxide and sodium silicate), hooked-end steel fibers (HESFs), basalt fibers (BFs), and polypropylene fibers (PPFs), as well as aggregates (gravel and sand). The effect of different geopolymer-based materials, reinforcing fibers, and different curing regimes on the mechanical, durability, and economic performance were analyzed. Results showed that the applied thermal curing regimes (oven curing or steam curing) had a considerable impact on durability performance, compressive strength, and flexural strength development, especially for GPC mixes involving high FA content. Cost analysis outcomes suggested that the most affordable option is GPCM1 (100% FA without fibers), but it demonstrates low strength under ambient curing conditions; RGCM4 (100% GGBS and 0.75% HESF) provided the best strength and durability option but at higher material cost; RGCM7 (50% FA, 50% GGBS, and 0.75% HSF) exhibited a balanced choice since it offer satisfied strength and durability performance with moderate cost compared to other options.

Construction Materials doi: 10.3390/constrmater5040080

Authors: Mai Megahed Mohamed AbouZeid

Three-dimensional concrete printing (3DCP) requires mixtures that develop sufficient early buildability while preserving open time for reliable interlayer bonding. This study investigates the time-dependent evolution of static yield stress for printable concretes incorporating three supplementary cementitious materials—metakaolin (MK), silica fume (SF), and biochar (BC)—used with either a polycarboxylate ether- (PCE) or naphthalene-based superplasticizer. Static yield stress was measured at 15, 30, and 45 min of concrete age using the stress-growth method with a shear vane apparatus. Performance targets were τs (15 min) ≤ 2.8 kPa, reflecting extrudability/pumpability; τs (30 min) ≤ 3.1 kPa, representing printability/open time; and τs (45 min) ≥ 3.4 kPa, representing buildability. Pooled Type-II ANOVA showed a highly significant SP effect (p < 0.001), a significant SCM × SP interaction (p = 0.031), and a significant time effect (p = 0.005), whereas SCM (p = 0.709) and SCM% (p = 0.914) were non-significant once interaction and time were included. Across SCMs, SNF–PCE gaps are ~0.2–0.8 kPa at 30 min (+7–30%) and ~0.4–1.3 kPa at 45 min (+12–45%), with the largest gaps in SF, intermediate in MK, and smallest in BC.

Construction Materials doi: 10.3390/constrmater5040079

Authors: Rafaela Pollon Giovani Jordi Bruschi Suéllen Tonatto Ferrazzo Arielle Cristina Fornari Eduarda Razador Lazzari Pedro Domingos Marques Prietto Eduardo Pavan Korf

The growing concern with carbon dioxide emissions from the cement industry has driven the search for alternative binders with lower environmental impact. Among these, alkali-activated cements (AACs) stand out due to their ability to produce cementitious matrices from aluminosilicate precursors and alkaline activators. However, comparisons between One-Part and Two-Part systems remain limited. This study evaluated the technical feasibility of producing AAC using sugarcane bagasse ash (SCBA) as precursor, carbide lime (CL) as calcium source, and sodium hydroxide (NaOH) as activator. Different parameters were tested, including NaOH molarities (1.0–2.5 M), SCBA/CL ratios (9.00–1.50), curing times (3, 7, and 28 days), and preparation methods. Mortars were produced at constant water/solid ratio of 1.40 and cured at room temperature (23 °C). Unconfined compressive strength (UCS) and leaching tests were performed, along with statistical analysis and Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) analyses. ACC synthesized by the Two-Part method (2.0 M NaOH, SCBA:CL 70:30) reached an UCS of 1.60 MPa at 28 days, compared to 1.39 MPa for the One-Part method. Curing time was identified as the most significant factor, followed by SCBA/CL ratio and activator molarity, while preparation method had minimal effect. The material developed alkali-activated gels, and leaching tests indicated no toxicity, although Ba concentrations exceeded regulatory limits for water quality. Potential applications include mine tailings stabilization, soil improvement, shallow foundations, and urban furniture production.

Construction Materials doi: 10.3390/constrmater5040078

Authors: Mustafa Thaer Hasan Alaa A. Abdul-Hamead Farhad M. Othman

The increasing demand for sustainable construction materials has prompted the recycling of construction and demolition waste in concrete manufacturing. This study investigates the feasibility of utilizing porcelain and brick waste as partial substitutes for natural sand in concrete with the objective of improving sustainability and preserving mechanical and durability characteristics. The experimental program was conducted in three consecutive phases. During the initial phase, natural sand was partially substituted with porcelain waste powder (PWP) and brick waste powder (BWP) in proportions of 25%, 50%, and 75% of the weight of the fine aggregate. During the second phase, polypropylene fibers were mixed at a dosage of 0.5% by volume fraction to enhance tensile and flexural properties. During the third phase, zinc oxide nanoparticles (ZnO-NPs) were utilized as a partial substitute for cement at concentrations of 0.5% and 1% to improve microstructure and strength progression. Concrete samples were tested at curing durations of 7, 28, and 91 days. The assessed qualities encompassed workability, density, water absorption, porosity, compressive strength, flexural strength, and splitting tensile strength. Microstructural characterization was conducted utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The findings indicated that porcelain waste powder markedly surpassed brick waste powder in all mechanical and durability-related characteristics, particularly at 25% and 50% sand replacement ratios. The integration of polypropylene fibers enhanced fracture resistance and ductility. Moreover, the incorporation of zinc oxide nanoparticles improved hydration, optimized the pore structure, and resulted in significant enhancements in compressive and tensile strength throughout prolonged curing durations. The best results were obtained with a mix of 50% porcelain sand aggregate, 1% zinc oxide nanoparticles as cement replacement, and 0.5% polypropylene fibers, for which the improvements in compressive strength, flexural strength, and splitting tensile strength were 39.5%, 46.2%, and 60%, respectively, at 28 days. The results confirm the feasibility of using porcelain and brick waste as sand replacements in concrete, as well as polypropylene fiber-reinforced concrete and polypropylene fiber-reinforced concrete mixed with zinc oxide nanoparticles as a sustainable option for construction purposes.

Construction Materials doi: 10.3390/constrmater5040077

Authors: Bouchra Bahja Abdeslam Tizliouine Lhaj El Hachemi Omari

This study investigates the fact that reinforcing geopolymers with natural fibers provides a practical way to improve their strength and durability. Offering environmental benefits compared to Portland cement, their mechanical performance still presents challenges. The particularity of this study lies in the pretreatment of natural fibers to limit their degradation within the alkaline geopolymer matrix. It also explores the effect of their length and content on matrix geopolymer. XRD (X-ray diffraction) analysis confirmed the crystalline structure of the geopolymer gels, unaffected by fiber inclusion. SEM (Scanning Electron Microscopy) observations showed a decrease or even disappearance of mineralization in treated sisal and palm fibers within the matrix, along with some partial detachment of the fibers. Optimal compressive strength was achieved using metakaolin and GGBS (Ground Granulated Blast-furnace slag). Incorporating 4% short palm fibers enhanced flexural strength, while long sisal fibers led to a 30% increase in flexural strength compared to short fibers, representing a 10.7% overall improvement. However, current geopolymer systems still face challenges such as low flexural strength and brittleness, which this study overcomes by incorporating processed natural fibers as sustainable reinforcements with optimal content.

Construction Materials doi: 10.3390/constrmater5040076

Authors: Shivam Kumar Deepthi Shenoy Vansh Vardhan Kiran Choudhary Laxman P. Kudva H. K. Sugandhini

The search for viable alternative resources is essential for advancing sustainable development in the construction industry. A significant global concern is the substantial generation of industrial waste, particularly coal ash byproducts such as fly ash (FA) and coal bottom ash (CBA) from thermal power plants (TPPs). India ranks as the third-largest producer of coal ash globally and the second-largest in Asia, generating approximately 105 million metric tonnes annually. While TPP-derived wastes have been extensively studied in masonry mortars, the potential of CBA as a partial or complete replacement for natural fine aggregates (NFA) in high-strength mortar (HSM) remains significantly underexplored. This study investigates the fresh, mechanical, and microstructural properties of mortar incorporating CBA as a substitute for NFA, specifically up to a 100% replacement level Flow table tests revealed improved workability with increasing CBA content, which is attributed to its porous microstructure; however, significant bleeding was observed at higher replacement levels (≥75%). The dry density consistently decreased with the addition of CBA with a reduction of up to 19.27% at full replacement. Ultrasonic pulse velocity (UPV) values declined with higher levels of CBA but improved with curing age. The mortar incorporating up to 100% CBA retains appreciable mechanical properties despite a progressive reduction in compressive strength (CS) with increasing CBA content. The observed compressive strengths for the different mixes were as follows: control mix (CM) at 36.72 MPa, mix with 25% CBA (CBA25) at 25.56 MPa, mix with 50% CBA (CBA50) at 19.69 MPa, mix with 75% CBA (CBA75) at 16 MPa, and mix with 100% CBA (CBA100) at 9.93 MPa. All mixes exceeded the minimum strength criteria, confirming their classification as HSMs at all replacement levels. These results highlight the potential of CBA as a sustainable alternative in construction materials, supporting efforts toward resource efficiency and environmental sustainability in the industry.

Construction Materials doi: 10.3390/constrmater5040075

Authors: Hamad I. Al Abdul Wahhab Waqas Rafiq Mohammad Ahsan Habib Ali Mohammed Babalghaith Suleiman Abdulrahman Shaban Shahzad

Polymer-based product usage in modern society is increasing day by day. Following usage, these inert products and hydrophobic materials contribute to environmental pollution, often accumulating as litter in ecosystems and contaminating water bodies. The rapid socio-economic development in the Kingdom of Saudi Arabia (KSA) has resulted in a significant increase in waste generation. This study was conducted on the utilization of recycled plastic waste (RPW) polymer along with commercial polymer (CP) for the modification of the local binder. The hot environmental conditions and increased traffic loading are the major reasons for the permanent deformation and thermal cracks on the pavements, which require improved and modified road performance materials. The Ministry of Transport and Logistical Support (MOTLS) in Saudi Arabia, along with other related agencies, spends a substantial amount of money each year on importing modifiers, including chemicals, hydrocarbons, and polymers, for modification purposes. This research was conducted to investigate and utilize available local recycled plastic materials. Comprehensive laboratory experiments were designed and carried out to enhance recycled plastic waste, including low-density polyethylene (rLDPE), high-density polyethylene (rHDPE), and polypropylene (rPP), combined with varying percentages of commercially available polymers such as Styrene-Butadiene-Styrene (SBS) and Polybilt (PB). The results indicated that incorporating recycled plastic waste expanded the binder’s susceptible temperature range from 64 °C to 70 °C, 76 °C, and 82 °C. The resistance to rutting was shown to have significantly improved by the dynamic shear rheometer (DSR) examination. Achieving the objectives of this research, combined with the intangible environmental benefits of utilizing plastic waste, provides a sustainable pavement development option that is also environmentally beneficial.

Construction Materials doi: 10.3390/constrmater5040074

Authors: Péter Primusz Balázs Kisfaludi Csaba Tóth József Péterfalvi

In Hungary, on-site mixed stabilization of cohesive soil is considered only as soil improvement not a proper pavement layer, therefore its bearing capacity is not taken into account when designing pavement. It was our hypothesis that on low-volume roads built on cohesive soil, lime or lime–cement stabilization can be an alternative to granular base layers. A case study was conducted to obtain initial results and to verify the research methodology. The efficacy of lime stabilization was evaluated across eight experimental road sections, with a view of assessing its structural and economic performance in comparison with crushed stone base layers reinforced with geo-synthetics. The results of the testing demonstrated elastic moduli of 120–180 MPa for the lime-stabilized layers, which closely matched the 200–280 MPa range observed for the crushed stone bases. The results demonstrated that lime stabilization offers a comparable load-bearing capacity while being the most cost-effective solution. Furthermore, this approach enhances sustainability by enabling the utilization of local soils, reducing reliance on imported materials, minimizing transport-related costs, and lowering carbon emissions. Lime stabilization provides a durable, environmentally friendly alternative for road construction, effectively addressing the challenges of material scarcity and rising construction costs while supporting infrastructure resilience. The findings highlight its potential to replace traditional base layers without compromising structural performance or economic viability.

Construction Materials doi: 10.3390/constrmater5040073

Authors: Fernando Fernández Marina Sánchez Pablo Gómez García Míriam Hernández Miguel Hurtado Yanjuan Chen Hubert Rahier Carlos Rodríguez

Reducing the carbon footprint of the construction sector is a growing priority. This study explores the potential of using submerged arc welding (SAW) slag as a precursor in the development of low-carbon geopolymeric materials for 3D printing. The influence of potassium hydroxide (KOH) molarity, partial replacement of ground granulated blast furnace slag (GGBFS) with SAW slag, and water-to-binder (w/b) ratio was evaluated in terms of fresh and hardened properties. Increasing KOH molarity delayed setting times, with the longest delays at 10 M and 12 M. The highest compressive strength (48.5 MPa at 28 days) was achieved at 8 M; higher molarities led to strength losses due to excessive precursor dissolution and increased porosity. GGBFS replacement increased setting times due to its higher Al2O3 and MgO content, which slowed geopolymerization. The optimized formulation, containing 20% SAW slag and activated with 8 M KOH at a w/b ratio of 0.29, exhibited good workability, extrudability, and shape retention. This mixture also performed best in 3D printing trials, strong layer adhesion and no segregation, although minor edge irregularities were observed. These results suggest that SAW slag is a promising sustainable material showing for 3D-printed geopolymers, with further optimization of printing parameters needed to enhance surface quality.

Construction Materials doi: 10.3390/constrmater5040072

Authors: Diego Llanos Aracely Huerta Jairsinho Huisa Victor Ariza Flores

This study presents a stochastic approach to assess bending moment demand in reinforced concrete beams subjected to vertical loads, incorporating uncertainties in material properties, geometry, and loading conditions. A Monte Carlo simulation framework was developed in Python version 3.9.3 using the OpenSeesPy library to analyze the variability of internal forces based on probabilistic input parameters. The analysis focuses on a four-span continuous beam representative of typical structural configurations in buildings. Probability distributions were assigned to key structural design parameters such as the unit weight of concrete (ρ), beam dimensions (b, h), column dimension (a), and applied loads, based on standard statistical assumptions and design guidelines. A total of 10,000 simulations were performed to obtain statistical descriptors of bending moment demand across the different spans. The results reveal significant variability in moment magnitudes, underscoring the importance of accounting for uncertainty in structural design. The proposed methodology enables the estimation of demand distributions and the identification of critical spans with higher sensitivity to parameter variations. Although the study does not evaluate structural capacity or failure probability, it contributes to the integration of stochastic techniques in the preliminary stages of design. Future work may include the incorporation of reliability 16 indices and comparisons with design code values.

Construction Materials doi: 10.3390/constrmater5040071

Authors: Chenhui Jiang Zefeng Chen Xuehong Gan

With the increasing application of manufactured sand, as one of the uncertain factors affecting the properties and performance of ready-mixed concrete proportioning with commonly used manufactured sand, residual flocculants in water-washed manufactured sand (WWMS) have received increased attention. Under certain prerequisites, a rapid detecting method for residual flocculants in WWMS was presented based on the pre-calibrated relationship between the Stormer viscosity of cement paste and the concentration of flocculants. Multi-dimensional and multi-factorial experiments were performed on cement paste, mortar and concrete orderly to explore the effects of flocculant content on the rheological (workability) and mechanical properties (compressive strength) of concrete. The results showed a good quantitative relationship between the Stormer viscosity and the flocculant content, and its mathematical formula depended on the type, molecular weight and content range of the flocculant. The residual flocculant contents in WWMS not only affected the workability of fresh concrete, but also the strength of hardened concrete to some extent.

Construction Materials doi: 10.3390/constrmater5030070

Authors: Ichebadu George Amadi Jeffrey Mahachi

Supplementary cementitious materials (SCMs) provide a practical solution for reducing greenhouse gas emissions associated with Portland cement production while enhancing the economy, performance, and service life of concrete and mortar. Currently, there is a significant disparity in the availability, supply, and utilisation levels of SCMs worldwide, particularly in South Africa. This paper presents an in-depth analysis of the characteristics and performance of various SCMs, including local availability, factors driving demand, production, and utilisation. The findings indicate that fly ash and limestone calcined clay are the most widely available SCM resources in South Africa, with deposits exceeding 1 billion tonnes each. Fly ash stockpiles continuously increase due to the reliance on coal-fired power plants for 85% of generated electricity and a low fly ash utilisation rate of 7%, significantly below international utilisation levels of 10–98%. Conversely, slag resources are depleting due to the steady decline of local steel production caused by energy and input costs, alongside the growing importation of steel products. Combined, the estimated production of slag and silica fume is about 1.4 million tonnes per annum, leading to their limited availability and utilisation in niche applications such as high-performance concrete and marine environments. Furthermore, 216,450 tonnes of SCM could potentially be processed annually from agricultural waste. In addition to quality, logistics, costs, and other challenges, this quantity can only replace 1.5% of clinker in South Africa, raising concerns about the viability of SCMs from agricultural waste. Based on its findings, this study recommends future research areas to enhance the performance, future availability, and sustainability of SCMs.

Construction Materials doi: 10.3390/constrmater5030069

Authors: Danah Alenezi Dema Mohammad Fatemah Alfoudari Manar Saeedi Refah Alajmi Enea Mustafaraj

This study investigates the use of untreated coconut coir fibers as a sustainable reinforcement in cement mortars, with emphasis on the combined effects of fiber content (0.5–2.0% by volume) and length (10–25 mm) on mechanical performance and water absorption. Sixteen mortar mixes were tested for water absorption, flexural and compressive strength, and microstructural characteristics. Results showed that moderate fiber addition significantly improved both strength and durability. The optimal mix (1.0% fiber, 15 mm length) achieved 8.36 MPa in flexural and 29.28 MPa in compressive strength, representing 61% and 131% improvements over the control, respectively. It also recorded the lowest water absorption (8.38%), attributed to improved fiber–matrix bonding and densification of the interfacial transition zone, as confirmed by Scanning Electron Microscopy. In contrast, excessive fiber dosages led to agglomeration, reduced workability, and diminished performance. A third-degree polynomial regression model was developed to predict mechanical properties based on fiber parameters. The findings demonstrate the feasibility of using untreated coconut waste fibers to enhance mortar performance while contributing to sustainable construction practices aligned with circular economy principles and SDGs. This work provides practical insights into fiber optimization and supports broader adoption of bio-based materials in cementitious systems.

Construction Materials doi: 10.3390/constrmater5030068

Authors: Zaid S. Aljoumaily Mohammed Z. Al-Mulali Amjad H. Albayati Teghreed H. Ibrahim

The utilization of sugarcane molasses (SCM), a byproduct of sugar refining, offers a promising bio-based alternative to conventional chemical admixtures in cementitious systems. This study investigates the effects of SCM at five dosage levels, 0.25%, 0.50%, 0.75%, 1.00%, and 1.25% by weight of cement, on cement mortar performance across fresh, mechanical, thermal, durability, and density criteria. A comprehensive experimental methodology was employed, including flow table testing, compressive strength (7, 14, and 28 days) and flexural strength measurements, embedded thermal sensors for real-time hydration monitoring, water absorption and chloride ion penetration tests, as well as 28-day density determination. Results revealed clear dose-dependent behavior, with SCM enhancing mortar flowability proportional to dosage, raising the spread diameter from 11.5 cm (control) to 20 cm at 1.25%. At 0.25% SCM, compressive strength (47.5 MPa at 28 days) and flexural strength (~2.9 MPa) were higher than those of the remaining SCM dosages, supported by sustained heat release and positive temperature differentials. However, dosages ≥ 0.5% drastically suppressed hydration kinetics and mechanical performance, with compressive strength falling below 10 MPa. Furthermore, high SCM content led to increased water absorption (up to 10.6%) and chloride permeability (CIP above 5100 C), while bulk density declined from 2250 kg/m3 to 2080 kg/m3 at 1.25% SCM. Statistical validation using one-way ANOVA confirmed that these differences across dosage levels were significant (p < 0.05), underscoring the importance of dosage optimization. This investigation confirms that low-dosage SCM (≤0.25%) can be an effective bio-additive, providing improved workability with negligible compromise in strength and durability. In contrast, higher dosages undermine matrix integrity and performance. Future work is recommended to assess long-term microstructural evolution, field exposure durability, and adaptability across diverse cementitious systems.

Construction Materials doi: 10.3390/constrmater5030067

Authors: Bishnu Kant Shukla Harshit Yadav Satvik Singh Shivam Verma Anoop Kumar Shukla Chetan Sharma

The transition toward sustainable infrastructure in the construction sector necessitates the practical integration of Circular Economy (CE) principles, particularly through the valorization of recycled materials in concrete applications. This review critically synthesizes recent advancements in the use of recycled polyethylene terephthalate (PET), glass powder, and crumb rubber as partial replacements for conventional aggregates in Ordinary Portland Cement (OPC)-based concrete. The incorporation of these secondary materials has demonstrated the ability to reduce the environmental footprint of concrete production—achieving up to 25% reductions in greenhouse gas emissions and diverting significant volumes of waste from landfills—while maintaining structural viability with compressive strength retention levels exceeding 90% in several optimized mix designs. Enhanced ductility, thermal resistance, and reduced density further support their application in specialized construction scenarios. Beyond material characterization, the review systematically examines implementation enablers, including regulatory alignment, life-cycle-based procurement, and design-for-deconstruction strategies. It also highlights critical gaps such as the absence of harmonized standards, variability in recycled material quality, and systemic barriers to market uptake. Addressing these challenges is essential for scaling CE integration and achieving measurable sustainability gains across the built environment. This study aims to inform policy, practice, and research trajectories by linking material innovation with operational frameworks that support regenerative construction systems.

Construction Materials doi: 10.3390/constrmater5030066

Authors: Anthony Brenes-Calderon Adriana Vargas-Nordcbeck Surendra Chowdari Gatiganti Josué Garita-Jimenez

This study evaluated the benefits of pavement preservation treatments across two climatic zones using data from the National Center for Asphalt Technology (NCAT) Pavement Preservation Group Study. Longitudinal data analysis was conducted to quantify pavement performance over time. Results indicate that in the freeze zone, treatments significantly improved pavement smoothness, as evidenced by reductions in the progression of the International Roughness Index (IRI), whereas similar trends were not observed in the no-freeze region, highlighting the need for further research to quantify the benefits in these zones. Life cycle cost analysis (LCCA) showed that selected preservation treatments reduced user costs by 54–57% due to lower excess fuel consumption, particularly in high-traffic corridors. These treatments also contributed to reductions in greenhouse gas (GHG) emissions by decreasing fuel use. Despite these findings, comprehensive, high-quality data are needed to fully evaluate the economic and environmental benefits of preservation treatments at the project level and to improve decision-making in pavement management strategies.

Construction Materials doi: 10.3390/constrmater5030065

Authors: Faris J. Thyab Zaid Hazim Al-Saffar Anas Ghaiath Ibrahim Helen Faris

Surface deterioration and paint peeling occur in historic buildings worldwide due to excessive moisture. Conventional coatings often fail to preserve these structures. In Mosul, Iraq, conventional paints often do not preserve historic structures. The article aims to use colored lime–gypsum mortar, which has significant potential to be used as a sustainable and appropriate candidate material for the restoration of historic structures. This is particularly relevant for the restoration of exterior elements or interior walls in humid environments. The flowability, strength (compressive, flexural, and tensile), and shrinkage cracking of several mortar mixtures with different lime–gypsum ratios and color additives were all part of the extensive testing. Every procedure closely followed the applicable international standards The mortar mixture identified as optimal (Mix A10), comprising a 1:1 lime-to-gypsum ratio with carefully calibrated pigment additives (0.5 g chromium oxide, 0.2 mL liquid oxide, and 0.5 g powder oxide), demonstrated superior mechanical properties and minimal shrinkage cracking. This composition was ideal due to its superior mechanical strength and reduced shrinkage cracking compared to pure gypsum mixtures. The colored lime–gypsum mortar is a sustainable material well-suited to the restoration of historic structures, and applicable to both interior and exterior elements in humid environments. Its low shrinkage cracking enhances durability and effectively prevents moisture ingress in moisture-sensitive cultural settings.

Construction Materials doi: 10.3390/constrmater5030064

Authors: Tomohiro Fujinaga Tomohiro Miyasaka Yousuke Kanou Shouichi Akiba

Latent stripping has become increasingly apparent in asphalt pavements, particularly in highway rehabilitation and international construction projects supported by Official Development Assistance (ODA) from the Government of Japan. Stripping accelerates structural deterioration, making countermeasures essential. However, in ODA projects, securing high-quality aggregates or evaluating local materials is often difficult due to environmental and budgetary constraints. This study focused on Surface Free Energy (SFE) as a small-sample evaluation method and developed ten types of styrene–butadiene–styrene (SBS) polymers to enhance interfacial adhesion by targeting aggregate surface functional groups. The SFE of each Polymer-Modified Bitumen (PMB) and thirteen aggregates was measured, and the work of adhesion and moisture sensitivity index (MSI) were calculated for all combinations. Twenty-one Hot-Mix Asphalts (HMA) were then prepared and evaluated using the Hamburg Wheel Tracking Test (HWTT) based on load cycles to stripping initiation (LCSN) and to 12.5 mm rut depth (LCST). The developed PMBs showed a higher work of adhesion, a lower MSI, and substantially increased LCSN and LCST values. Strong negative correlations were observed between MSI and both HWTT indicators, confirming the utility of SFE-based MSI for material screening. This study demonstrates that interface-targeted PMBs can improve stripping resistance, thereby promoting the use of lower-quality aggregates in durable pavements.

Construction Materials doi: 10.3390/constrmater5030063

Authors: Ferdinand Niyonyungu Aurobindo Ogra Ntebo Ngcobo

The reuse of Waste Foundry Sand (WFS) in construction remains constrained by fragmented research, unclear regulatory pathways, and inconsistent assessments of environmental safety and material performance. This study introduces a novel decision-making framework that systematically integrates mechanical performance metrics and leachate toxicity data to classify WFS into three categories: Approved, Reusable with Treatment, or Rejected. The framework is based on a bibliometric analysis of 822 publications and a meta-analysis of 45 experimental mix designs and 30 peer-reviewed leachate studies. Normalized compressive strength (NSR), water-to-cement (w/c) ratio, and heavy metal leachate concentrations are used as screening criteria. Thresholds are benchmarked against regulatory limits from the United States Environmental Protection Agency (EPA), the European Union Landfill Directive, and South Africa’s National Waste Standards. Validation using field data from a foundry in Gauteng Province, South Africa, confirms the framework’s practicality and adaptability. Results indicate that over 80 percent of WFS samples comply with environmental thresholds, and mixes with 10-to-30 percent WFS substitution often outperform control specimens in terms of compressive strength. However, leachate exceedances for cobalt and lead in certain chemically bonded sands highlight the need for batch-specific evaluation and potential treatment. The proposed framework supports data-driven, transparent reuse decisions that enhance environmental compliance and promote circular material flows in the built environment. Future work should focus on digital implementation, life-cycle monitoring, and expanding the framework to other industrial byproducts.

Construction Materials doi: 10.3390/constrmater5030062

Authors: Sergey V. Panin Mengxu Qi Dmitry Yu. Stepanov Mikhail V. Burkov Valery E. Rubtsov Yury V. Kushnarev Igor Yu. Litovchenko

The aim of this study was to investigate microstructure and the mechanical and operational characteristics of thick and thin walls 3D-built by electron beam additive manufacturing (EBAM). In addition, the milling parameters (rotation speed, feed, and cutting width) were optimized based on simultaneous assessments of Ra roughness on the machined surfaces and material removing rate values. The wall dimensions did not exert a noticeable effect on their chemical compositions, as compared with the original wires used for 3D printing. In comparison, the strength characteristics of the wrought steel (cold-rolled plate) were higher due to finer grains, with both ferrite content and dislocation density being greater as well. In the 3D building process, multiple thermal cycles gave rise to the formation of elongated columnar grains, reducing the strength characteristics. The corrosion rate of the wrought steel was almost twice those of the 3D-printed blanks because of the higher content of both ferrite and twins. By assessing the machinability of the EBAM-built blanks using the stationary milling machine, the cutting forces were comparable due to similar mechanical properties (including microhardness). To improve the removing rate values and reduce the cutting forces, it is recommended to enhance the cutting speeds while not increasing the feeds. For the semi-industrial milling machine, both linear multiple regression and nonlinear neural network models were applied. An integrated approach was proposed that rationally determined both additive manufacturing and post-processing parameters based on a combination of express assessment and analysis of the mechanical, operational, and technological characteristics of built products within a single laboratory complex.

Construction Materials doi: 10.3390/constrmater5030061

Authors: Sergey Gutnikov Pavel Pastushkov

Hydrogen is emerging as a crucial energy carrier, yet effective insulation for liquid hydrogen (LH2) storage remains a significant challenge. This study focuses on evaluating the thermal properties of mineral fiber insulation at cryogenic temperatures, utilizing the guarded hot plate method to determine thermal conductivity values between 223 K (−150 °C) and 573 K (300 °C). The measured effective thermal conductivities ranged from 0.0147 to 0.2113 W/mK, varying with temperature. Notably, while high-density materials can be accurately modeled using linear approximations, low-density materials exhibit significant nonlinearity, with discrepancies in thermal conductivity estimates reaching up to 30%. The implications of this research highlight the necessity for precise thermal property assessments in the design of cryogenic systems, emphasizing their potential impact on energy efficiency and reduced carbon emissions. Ultimately, these findings provide essential insights for advancing cryogenic insulation technologies, supporting the broader transition to sustainable hydrogen energy solutions.

Construction Materials doi: 10.3390/constrmater5030060

Authors: Madiha Z. J. Ammari Halil Sezen Jose Castro

In this research work, five different types of post-consumer plastics were mechanically ground into fine aggregate, and each type was used to prepare 2 in. (50 mm) mortar cubes by partial volumetric replacement of the sand. The purpose is to evaluate the effect of the plastic type and its shape on the density and the compressive strength of concrete. The plastic products used in this study are usually not collected by curbside recycling facilities and are discarded in landfills or incinerated. The different types of plastics investigated were Polyethylene terephthalate (PET), High-Density Polyethylene (HDPE), Polypropylene (PP), Polystyrene (PS), and Acrylonitrile Butadiene Styrene (ABS). A total of 180 cubes with 5%, 10%, and 15% replacement were prepared and tested for their densities at the age of 28 days and their compressive strengths at the ages of 7 and 28 days. This work concluded by proposing general equations to predict the reduction in the density and compressive strength of the mortar with the increment in the plastic replacement.

Construction Materials doi: 10.3390/constrmater5030059

Authors: Samuel Ramírez-Arellanes Fernando Montejo-Alvaro Heriberto Cruz-Martínez Hugo Rojas-Chávez Jose Manuel Mendoza-Rangel Víctor Alberto Franco-Luján

The manufacture of Portland cement (PC) emits a significant amount of CO2 into the atmosphere. Therefore, the partial replacement of PC by supplementary cementitious materials (SCMs) possessing pozzolanic properties is considered a viable strategy to reduce its environmental impact. Recently, waste glass (WG) has been explored as a potential SCM. However, due to the wide variety of glass types and their differing physical and chemical properties, not all WG can be universally considered suitable for this purpose; therefore, this study investigates the use of recycled WG as an SCM for the partial replacement of PC. Two types of WG were evaluated: green waste glass from wide bottles (GWG) and laboratory waste glass (LWG), and their performance was compared to that of fly ash (FA). The physical, mechanical, and pozzolanic properties of the materials were assessed. Results show that both types of WG exhibit particle size distributions comparable to PC and have contents of SiO2, Al2O3, and Fe2O3 exceeding 70%. Chemical, mineralogical, and pozzolanic analyses revealed that both GWG and LWG presented higher pozzolanic activity than FA, particularly at later ages. Notably, LWG demonstrated the most significant contribution to mechanical strength development. These findings suggest that recycled waste glass, especially LWG, can serve as a viable and sustainable SCM, contributing to the reduction of the environmental footprint associated with Portland cement production.

Construction Materials doi: 10.3390/constrmater5030058

Authors: Abdelhak Badache Noureddine Latroch Mostefa Hacini Ahmed Soufiane Benosman Mohamed Mouli Yassine Senhadji Walid Maherzi

This study investigates sustainable mortars using lightweight synthetic sand (LSS), made from dune sand and recycled PET bottles, to replace natural sand (0–100% by volume). This aligns with circular economy principles by valorizing plastic waste into a construction aggregate. LSS is produced via controlled thermal treatment (250 ± 5 °C, 50–60 rpm), crushing, and sieving (≤3.15 mm), leading to a significantly improved interfacial transition zone (ITZ) with the cement matrix. The evaluation included physico-mechanical tests (density, strength, UPV, dynamic modulus, ductility), thermal properties (conductivity, diffusivity, heat capacity), porosity, sorptivity, alkali–silica reaction (ASR), and SEM. The results show LSS incorporation reduces mortar density (4–23% for 25–100% LSS), lowering material and logistical costs. While compressive strength decreases (35–70%), these mortars remain suitable for low-stress applications. Specifically, at ≤25% LSS, composites retain 80% of their strength, making them ideal for structural uses. LSS also enhances ductility and reduces dynamic modulus (18–69%), providing beneficial flexibility. UPV decreases (8–39%), indicating improved acoustic insulation. Thermal performance improves (4–18% conductivity reduction), suggesting insulation applicability. A progressive decrease in sorptivity (up to 46%) enhances durability. Crucially, the lack of ASR susceptibility reinforces long-term durability. This research significantly contributes to the repurposing of plastic waste into sustainable cement-based materials, advancing sustainable material management in the construction sector.

Construction Materials doi: 10.3390/constrmater5030057

Authors: Ferdinand Niyonyungu Aurobindo Ogra Ntebo Ngcobo

The significant expansion of the construction sector and corresponding depletion of natural sand resources have intensified the search for sustainable alternatives, with waste foundry sand (WFS) emerging as a promising candidate. This systematic review evaluates the environmental performance and engineering feasibility of using WFS as a substitute for natural sand in construction. A PRISMA-guided search identified 152 peer-reviewed studies published between 2001 and 2024, which were categorized into four thematic areas: material characterization, construction applications, environmental impacts, and regulatory frameworks. The findings indicate that substituting 10–30% of natural sand with WFS in concrete and asphalt can deliver compressive strength within ±5% of control mixes and reduce water absorption by 5–15% at optimal replacement levels. However, contamination risks remain a concern, as chromium and copper concentrations in raw WFS have been reported at up to 931 mg/kg and 3318 mg/kg, respectively. To address these risks and ensure responsible reuse, a six-stage framework is proposed in this study, comprising end-of-waste classification, contaminant assessment, material preprocessing, certification, and regulatory monitoring. A comprehensive decision tree is also presented to guide the feasibility assessment of WFS reuse based on contaminant levels and material performance.

Construction Materials doi: 10.3390/constrmater5030056

Authors: Francois Mouawad Farah Homsi Fadi Geara Rayan Mina

The integration of sustainable materials such as fly ash, blast-furnace slag, recycled aggregates, and seawater into concrete mixes offers significant potential for reducing the environmental impact of construction. However, traditional experimental methods for determining the compressive strength of these concrete mixes are time-consuming and resource-intensive. This study leverages Artificial Neural Networks (ANNs) and Machine Learning (ML) to develop a predictive model for the compressive strength of sustainable concrete, using a dataset of 768 concrete mix samples. Input variables include the concrete age as well as concrete composition, including cement, water, fine and coarse aggregates, seawater, fly ash, blast-furnace slag, and superplasticizer contents, while the output is the compressive strength. The developed model captures the non-linear relationships among these variables to predict compressive strength efficiently. The best ANN model achieved a test loss of 0.051, demonstrating its ability to accurately predict compressive strength and reduce reliance on traditional testing methods. Moreover, the model’s results were compared with those of alternative algorithms to ensure its validity. These findings highlight the potential of machine learning in advancing sustainable construction practices. A relevant future research direction is to analyze feature importance in machine learning models to identify key variables and guide more effective optimization and decision-making, in addition to extending their application to other material properties and advanced concrete mixes.

Construction Materials doi: 10.3390/constrmater5030055

Authors: Lu Gao Zia Ud Din Kinam Kim Ahmed Senouci

This study investigates the deterioration of skid resistance and surface macrotexture following preventive maintenance using micro-milling techniques. Field data were collected from 31 asphalt pavement sections located across four climatic zones in Texas. The data encompasses a variety of surface types, milling depths, operational speeds, and drum configurations. A standardized data collection protocol was followed, with measurements taken before milling, immediately after treatment, and at 3, 6, 12, and 18 months post-treatment. Skid number and Mean Profile Depth (MPD) were used to evaluate surface friction and texture characteristics. The dataset was reformatted into a time-series structure with 930 observations, including contextual variables such as climatic zone, treatment parameters, and baseline surface condition. A comparative modeling framework was applied to predict the deterioration trends of both skid resistance and macrotexture over time. Eight regression models, including linear, tree-based, and ensemble methods, were evaluated alongside a time series Transformer model. The results show that the Transformer model achieved the highest prediction accuracy for skid resistance (R2 = 0.981), while Random Forest performed best for macrotexture prediction (R2 = 0.838). The findings indicate that the degradation of surface characteristics after preventive maintenance is non-linear and influenced by a combination of environmental and operational factors. This study demonstrates the effectiveness of data-driven modeling in supporting transportation agencies with pavement performance forecasting and maintenance planning.

Construction Materials doi: 10.3390/constrmater5030054

Authors: Zhaochang Zhang Yudong Luo Yonghong Miao Enquan Zhou Zhiwei Yan Guiyu Zhang

Coal is still China’s primary energy source, and the production process of coal produces industrial byproduct coal gangue. This study explores the possibility of using industrial byproducts of thermal power generation, fly ash (FA) and calcined coal gangue (CCG), as a partial (10% and 20%) substitute for cement in construction materials. Methodical research was conducted to determine how these two substances affect the microstructure and macroscopic characteristics of cement-based materials. Macroscopic performance test findings indicate that replacing 20% of cement with CCG had no discernible effect on the specimens’ performance. At the same time, adding FA required 28 days to be comparable to the control group. Mercury intrusion porosimetry (MIP) test results show that using CCG can refine microscopic pores. Additional hydration products could be produced by these materials, according to analyses using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The production of hydration products by CCG to fill the microscopic pores was further demonstrated by scanning electron microscopy (SEM) pictures. After 28 days of hydration, a layer of hydration products developed on the surface of FA. When supplementary cementitious materials (SCMs) were added, calcium hydroxide (CH) was consumed by interacting with FA and CCG to form additional hydration products, according to thermogravimetric analysis (TG) data after 28 days. Furthermore, an evaluation of FA and CCG’s effects on the environment revealed that their use performed well in terms of sustainable development.

Construction Materials doi: 10.3390/constrmater5030053

Authors: Sergey V. Panin Andrey V. Filippov Mengxu Qi Zeru Ding Qingrong Zhang Zeli Han

The study is motivated by the application of dry finish milling for post-build processing of additive Ti6Al4V blanks, since the use of neither lubricant nor coolants has been attracting increasing attention due to its environmental benefits, non-toxicity, and the elimination of the need for additional cleaning processes. For end mills, wear patterns were investigated upon finish milling of the SLM Ti6Al4V samples under various machining conditions (by varying the values of radial depth of cut and feed values at a constant level of axial depth of cut and cutting speed). When using all the applied milling modes, the identical tool wear mechanism was revealed. Built-up edges mainly developed on the leading surfaces, increasing the surface roughness on the SLM Ti6Al4V samples but protecting the cutting edges. However, abrasive wear was mainly characteristic of the flank surfaces that accelerated peeling of the protective coatings and increased wear of the end mills. The following milling parameters have been established as being close to rational ones: Vc = 60 m/min, Vf = 400 mm/min, ap = 4 mm, and ae = 0.4 mm. They affected the surface roughness of the SLM Ti6Al4V samples in the following way: max cutting thickness—8 μm; built-up edge at rake surface—50 ± 3 μm; max wear of flank surface—15 ± 1 μm; maximum adherence of workpiece. Mode III provided the maximum MRR value and negligible wear of the end mill, but its main disadvantage was the high average surface roughness on the SLM Ti6Al4V sample. Mode II was characterized by both the lowest average surface roughness and the lowest wear of the end mill, as well as an insufficient MRR value. Since these two modes differed only in their feed rates, their values should be optimized in the range from 200 to 400 mm/min.

Construction Materials doi: 10.3390/constrmater5030052

Authors: Hernan Patricio Moyano-Ayala Marisa Sofia Fernandes Dinis-Almeida

The increasing demand for sustainable practices in road construction has prompted the search for environmentally friendly and cost-effective materials. This study explores the incorporation of reclaimed asphalt pavement (RAP) and Panasqueira mine waste (greywacke aggregates) as full replacements for virgin aggregates in hot mix asphalt (HMA), aligning with the objectives of UN Sustainable Development Goal 9. Three asphalt mixtures were prepared: a reference mixture (MR) with granite aggregates, and two modified mixtures (M15 and M20) with 15% and 20% RAP, respectively. All mixtures were evaluated through Marshall stability, stiffness modulus, water sensitivity, and wheel tracking tests. The results demonstrated that mixtures containing RAP and mine waste met Portuguese specifications for surface courses. Specifically, the M20 mixture showed the highest stiffness modulus, improved moisture resistance, and the best performance against permanent deformation. These improvements are attributed to the presence of stiff aged binder in RAP and the mechanical characteristics of the greywacke aggregates. Overall, the findings confirm that the combined use of RAP and mining waste provides a technically viable and sustainable alternative for asphalt pavement construction, contributing to resource efficiency and circular economy goals.

Construction Materials doi: 10.3390/constrmater5030051

Authors: Hamsavathi Kannan Sathish Kumar Veerappan Madappa V. R. Sivasubramanian

Reinforced concrete (RC) deep beams constructed with low-strength concrete are susceptible to sudden splitting failures in the strut region due to shear–compression stresses. To mitigate this vulnerability, various strengthening techniques, including steel plates, fiber-reinforced polymer sheets, and cementitious composites, have been explored to confine the strut area. This study investigates the structural performance of RC deep beams with low-strength concrete, strengthened externally using an Engineered Cementitious Composite (ECC) layer. To ensure effective confinement and uniform shear distribution, shear reinforcement was provided at equal intervals with configurations of zero, one, and two vertical shear reinforcements. Four-point bending tests revealed that the ECC layer significantly enhanced the shear capacity, increasing load-carrying capacity by 51.6%, 54.7%, and 46.7% for beams with zero, one, and two shear reinforcements, respectively. Failure analysis through non-linear finite element modeling corroborated experimental observations, confirming shear–compression failure characterized by damage in the concrete struts. The strut-and-tie method, modified to incorporate the tensile strength of ECC and shear reinforcement actual stress values taken from the FE analysis, was used to predict the shear capacity. The predicted values were within 10% of the experimental results, underscoring the reliability of the analytical approach. Overall, this study demonstrates the effectiveness of ECC in improving shear performance and mitigating strut failure in RC deep beams made with low-strength concrete.

Construction Materials doi: 10.3390/constrmater5030050

Authors: Phouthanouthong Xaysombath Nattakan Soykeabkaew Darunee Wattanasiriwech Suthee Wattanasiriwech

This study evaluates the influence of fiber type, geometry, and interfacial behavior on the physical and mechanical performance of cementitious composites reinforced with recycled pulp from beverage cartons (RPBC), bamboo fiber (BF), and eucalyptus fiber (EF) as the sole reinforcing agents. The BF was rounded in shape and had the highest aspect ratio, while the ribbon-shaped EF exhibited the highest tensile strength index. The RPBC fibers were fibrillated and the shortest, with a ribbon shape. Flexural strength results showed that RPBCC achieved a maximum strength that was 47.6% higher than the control specimen (0% fiber), outperforming both BF- and EF-reinforced counterparts. This superior performance is attributed to the higher fibrillation level of the ribbon-shaped RPBC fibers, which promoted better fiber–matrix bonding. As the fiber content increased, the bulk density of EFC and BFC decreased linearly, while RPBC composites showed only a modest decrease in density. Porosity steadily increased in EFC and BFC, whereas a non-linear trend was observed in RPBCC, likely due to its unique morphology and fibrillation. Conversely, EFC exhibited significantly higher maximum fracture toughness (3600 J/m2 at 10 wt.%) compared to PBFCC (1600 J/m2 at 14 wt.%) and BFC (1400 J/m2 at 14 wt.%). This enhancement is attributed to extensive fiber pullout mechanisms and increased energy absorption during crack propagation. Overall, all composite types demonstrated flexural strength values above 4 MPa, placing them in the Grade I category. Those reinforced with 10–14% RPBC exhibited strengths of 11–12 MPa, categorizing them as Grade II according to ASTM C1186-02.

Construction Materials doi: 10.3390/constrmater5030049

Authors: Saikrishna Chelluri Nabil Hossiney Sarath Chandra Patrick Bekoe Mang Tia

The construction of concrete pavements has increased due to their better durability, lifespan, and lower maintenance costs. However, this has resulted in the increased consumption of Portland cement, which is one of the major contributors to carbon emissions. Consequently, the research on alternative binders such as geopolymer concrete has increased in recent times. There are several research studies that investigate the feasibility of geopolymer concrete as a construction material, with limited studies exploring its application in concrete pavements. Therefore, this review study explores the material properties of geopolymer concrete pertinent to the performance of concrete pavements. It also discusses the potential of various industrial and agricultural waste as precursor material in geopolymer concrete. The findings of this paper show that most of the studies used fly ash and ground granulated blast furnace slag (GGBFS) as precursor material in geopolymer pavement-quality concrete, and there is a vast scope in the exploration of other industrial and agricultural waste as precursor material. The mechanical and durability properties of geopolymer pavement-quality concrete are superior to conventional pavement concrete. It is also observed that the drying shrinkage and coefficient of thermal expansion of geopolymer pavement-quality concrete are lower than those of conventional pavement concrete, and this will positively benefit the long-term performance of concrete pavements. The results of fatigue analysis and mechanical load test on the geopolymer pavement-quality concrete indicate its improved performance when compared to the conventional pavement concrete.

Construction Materials doi: 10.3390/constrmater5030048

Authors: Fotini Kesikidou Kyriakos Koktsidis Eleftherios K. Anastasiou

Alkali-activated building materials have attracted the interest of many researchers due to their low cost and eco-efficiency. Different binders with different chemical compositions can be used for their production, so the reaction mechanism can become complex and the results of studies can vary widely. In this work, several alkali-activated mortars based on marginal by-products as binders, such as high calcium fly ash and ladle furnace slag, are investigated. Their mechanical (flexural and compressive strength, ultrasonic pulse velocity, and modulus of elasticity) and physical (porosity, absorption, specific gravity, and pH) properties were determined. After evaluating the mechanical performance of the mortars, the optimum mixture containing fly ash, which reached 15 MPa under compression at 90 days, was selected for the production of precast compressed slabs. Steel or glass fibers were also incorporated to improve their ductility. To reduce the density of the slabs, 60% of the siliceous sand aggregate was also replaced with recycled polyethylene terephthalate (PET) plastic aggregate. The homogeneity, density, porosity, and capillary absorption of the slabs were measured, as well as their flexural strength and fracture energy. The results showed that alkali activation can be used to improve the mechanical properties of weak secondary binders such as ladle furnace slag and hydrated fly ash. The incorporation of recycled PET aggregates produced slabs that could be classified as lightweight, with similar porosity and capillary absorption values, and over 65% achieved strength compared to the normal weight slabs.

Construction Materials doi: 10.3390/constrmater5030047

Authors: Thusitha Ginigaddara Pasadi Devapura Vanissorn Vimonsatit Michael Booy Priyan Mendis Rish Satsangi

This study presents a detailed and comprehensive investigation into the macro-scale performance, strength gain mechanisms, environment and economic performance of graphene oxide (GO)-enhanced low-emission concrete. A comprehensive experimental program evaluated fresh and hardened properties, including slump retention, bleeding, air content, compressive, flexural, and tensile strength, drying shrinkage, and elastic modulus. Scanning Electron Microscopy (SEM), energy-dispersive spectroscopy (EDS), Thermogravimetric analysis (TGA) and proton nuclear magnetic resonance (1H-NMR) was employed to examine microstructural evolution and early age water retention, confirming GO’s role in accelerating cement hydration and promoting C-S-H formation. Optimal performance was achieved at 0.05% GO (by binder weight), resulting in a 25% increase in 28-day compressive strength without compromising workability. This outcome is attributed to a tailored, non-invasive mixing strategy, wherein GO was pre-dispersed during synthesis and subsequently blended without the use of invasive mixing methods such as high shear mixing or ultrasonication. Fourier-transform infrared (FTIR) spectroscopy further validated the chemical compatibility of GO and PCE and confirmed the compatibility and efficiency of the admixture. Sustainability metrics, including embodied carbon and strength-normalized cost indices (USD/MPa), indicated that, although GO increased material cost, the overall cost-performance ratio remained competitive at breakeven GO prices. Enhanced efficiency also led to lower net embodied CO2 emissions. By integrating mechanical, microstructural, and environmental analyses, this study demonstrates GO’s multifunctional benefits and provides a robust basis for its industrial implementation in sustainable infrastructure.

Construction Materials doi: 10.3390/constrmater5030046

Authors: Gaurav Kumar Tushar Bansal Dayanand Sharma

This study explores the use of embedded piezo sensor (EPS) employing the Electro-Mechanical Impedance (EMI) technique for real-time corrosion monitoring in reinforced E-waste concrete exposed to chloride-laden environments. With the growing environmental concerns over electronic waste (E-waste) and the demand for sustainable construction practices, printed circuit board (PCB) materials were incorporated as partial replacements for coarse aggregates in concrete. The experiment utilized M30-grade concrete mixes, substituting 15% of natural coarse aggregates with E-waste, aiming to assess both sustainability and structural performance without compromising durability. EPS configured with Lead Zirconate Titanate (PZT) patches were embedded into both conventional and E-waste concrete specimens. The EPS monitored the changes in the form of conductance and susceptance signatures across a 100–400 kHz frequency range during accelerated corrosion exposure over a 60-day period in a 3.5% NaCl solution. The corrosion progression was evaluated qualitatively through electrical impedance signatures, visually via rust formation and cracking, and quantitatively using the Root Mean Square Deviation (RMSD) of EMI signatures. The results showed that the EMI technique effectively captured the initiation and propagation stages of corrosion. E-waste concrete exhibited earlier and more severe signs of corrosion compared to conventional concrete, indicated by faster increases and subsequent declines in conductance and susceptance and higher RMSD values during the initiation phase. The EMI-based system demonstrated its capability to detect microstructural changes at early stages, making it a promising method for Structural Health Monitoring (SHM) of sustainable concretes. The study concludes that while the use of E-waste in concrete contributes positively to sustainability, it may compromise long-term durability in aggressive environments. However, the integration of EPS and EMI offers a reliable, non-destructive, and sensitive technique for real-time corrosion monitoring, supporting preventive maintenance and improved infrastructure longevity.

Construction Materials doi: 10.3390/constrmater5030045

Authors: Stavros Kalampokis Jan Valentin Evangelos Manthos Avraam A. Konstantinidis

The present study concerns the utilization of spent coffee grounds (SCGs) as an alternative bio-based modifier for a petroleum-based penetration grade 70/100 bitumen at 5%, 10% and 15% by weight of bitumen. The conventional properties of the binders were examined with a series of penetration, ring and ball, elastic recovery, dynamic viscosity and storage stability tests. Their rheological properties were assessed with a Dynamic Shear Rheometer. The aforementioned tests were conducted before and after applying a short-term ageing protocol to quantify the ageing susceptibility of the binders using different rheological ageing metrics. Furthermore, a statistical analysis was conducted to discover whether any correlations exist between the conventional and rheological properties of the binders. It was observed that spent coffee grounds can be incorporated into bitumen at an optimal content of up to 5% without downgrading the binder’s rheological properties or its structural integrity. Additionally, the bio-modifier slightly improved the ageing resistance of bitumen. Finally, the ring and ball test’s results had the strongest correlation with the DSR findings.

Construction Materials doi: 10.3390/constrmater5030044

Authors: Carlos Guillermo Vargas Febres Juan Serra Lluch Ana Torres Barchino Edwin Roberto Gudiel Rodríguez

Lime plaster has historically been a key material in the preservation of architectural heritage in Peru; however, its availability has been restricted by state regulations that limit its production and commercialization. This study evaluates the performance of paints formulated with inorganic pigments extracted from soils in the Cusco valley, combined with natural and synthetic binders, as a sustainable alternative for the protection of heritage buildings in this Andean region characterized by high altitude, wide thermal variations, and high solar radiation. Adhesion, hardness, drying time, and weather resistance tests were conducted according to applicable ASTM standards for architectural coatings. The results show that these formulations exhibit good adhesion to historic surfaces and greater durability against extreme environmental conditions compared to traditional lime plaster. Their potential compatibility with historic substrates and lower environmental impact suggest that these paints represent a viable alternative in sustainable conservation strategies; however, further studies are needed to more accurately characterize the mineralogical composition of the pigments used.

Construction Materials doi: 10.3390/constrmater5030043

Authors: Konstantina Georgouli Andreas Loizos

This research aims to investigate the possibility of measuring dielectric constant as an alternative proxy for estimating E* through a non-destructive procedure. An experimental program was conducted on dense-graded (DG) and open-graded (OG) asphalt mixtures, where variable asphalt contents and compaction levels were controlled to achieve different air voids. The measurements of dielectric constant were performed with a Percometer, and E* values were obtained using standard laboratory tests. For DG mixtures, a clear correlation was observed between dielectric constant, air void content and effective binder ratio. The less consistent relationships for OG mixtures were likely due to the more heterogeneous structure of the OG mixtures, the conductive slag aggregates and a limited dataset. Using dielectric values, two predictive models were developed (DIME_DG and DIME_OG), with the former showing higher reliability. Verification with independent specimens confirmed model robustness. This dielectric-based approach offers a practical, cost-effective alternative to traditional modulus testing. The key innovation of this study is the integration of the asphalt mix dielectric constant into established dynamic modulus predictive models, offering a novel approach that enhances the sensitivity of these models to mixture-specific characteristics beyond traditional volumetric and binder properties.

Construction Materials doi: 10.3390/constrmater5030042

Authors: Sunday U. Azunna Farah N. A. A. Aziz Raizal S. M. Rashid Ernaleza B. Mahsum

Rubberized concrete is a more environmentally friendly material than natural concrete as it helps to reduce rubber disposal issues and has superior impact resistance. Geopolymer concrete, on the other hand, is an economical concrete with higher mechanical properties than nominal concrete that uses fly ash and slag, among other industrial solid wastes, to lower carbon footprints. Rubberized geopolymer concrete (RuGPC) combines the advantages of both concrete types, and a thorough grasp of its dynamic compressive characteristics is necessary for its use in components linked to impact resistance. Despite the advantages of RuGPC, predicting its mechanical characteristics is sometimes difficult because of variations in binder type and combination. This research investigated the combined effect of ground granulated blast furnace slag (GGBFS) and fly ash (FA) on the workability, compressive strength, and stress–strain characteristics of RuGPC with rubber at 0%, 10%, and 20% fine aggregate replacement. Thereafter, energy absorption and ductile characteristics were evaluated through the concrete toughness and ductility index. Numerical models were proposed for the cube compressive strength, modulus of elasticity, and peak strain of RuGPC at different percentages of crumb rubber. It was found that RuGPC made with GGBFS/FA had similar stress–strain characteristics to FA- and MK-based RuGPC. At 20% of crumb rubber aggregate replacement, the workability, compressive strength, modulus of elasticity, and peak stress of RuGPC reduced by 8.33%, 34.67%, 43.42%, and 44.97%, while Poisson’s ratio, peak, and ultimate strain increased by 30.34%, 8.56%, and 55.84%, respectively. The concrete toughness and ductility index increased by 22.4% and 156.67%. The proposed model’s calculated results, with R2 values of 0.9508, 0.9935, and 0.9762, show high consistency with the experimental data. RuGPC demonstrates high energy absorption capacity, making it a suitable construction material for structures requiring high-impact resistance.

Construction Materials doi: 10.3390/constrmater5020041

Authors: Rubén Rodríguez Elizalde

The Palma Cathedral, a landmark of Mediterranean Gothic architecture, features some of the most structurally daring slender piers in European ecclesiastical design. This study examines the role of marés stone—a local marine calcarenite—in enabling such architectural feats despite its inherent fragility. A multi-technique, non-invasive diagnostic campaign was conducted, including visual inspection, portable microscopy, and infrared thermography, to evaluate the physical condition and behavior of the stone under structural and environmental stress. The results reveal widespread deterioration processes—granular disintegration, alveolization, biological colonization, and structural cracking—exacerbated by the stone’s high porosity and exposure to marine aerosols and thermal fluctuations. Thermographic analysis highlighted moisture retention zones and hidden material discontinuities, while crack monitoring confirmed long-standing, localized structural strain. These findings demonstrate that the Cathedral’s formal audacity was grounded in a refined empirical understanding of marés’ properties. The study underscores the importance of material-based diagnostics for the sustainable conservation of Gothic heritage architecture.

Construction Materials doi: 10.3390/constrmater5020040

Authors: Mustafa Mohammed Jaleel Mustafa Albdairi Ali Almusawi

Iraq’s extreme summer temperatures pose critical challenges to pavement durability, as conventional asphalt mixtures often fail under prolonged thermal stress. This paper provides a comparative evaluation of the high-temperature performance of unmodified (40/50 penetration grade) and polymer-modified (PG 76-10) asphalt mixtures for the asphalt course layer. Marshall stability, flow, and stiffness were measured at elevated temperatures of 60 °C, 65 °C, 70 °C, and 75 °C after short-term (30 min) and extended (24 h) conditioning. Results show that while both mixtures experienced performance degradation as the temperature increased, the polymer-modified mixture consistently exhibited superior thermal resistance, retaining approximately 9% higher stability and 28% higher stiffness, and displaying 18% lower flow deformation at 75 °C compared to the unmodified mixture. Stability degradation rate (SDR), stiffness degradation rate (SiDR), and flow increase rate (FIR) analyses further confirmed the enhanced resilience of PG 76-10, showing nearly 39% lower FIR under thermal stress. Importantly, PG 76-10 maintained performance within specification thresholds under all tested conditions, unlike the conventional 40/50 mixture. These findings emphasize the necessity of adapting mix design standards to regional climatic realities and support the broader adoption of polymer-modified asphalt binders to enhance pavement service life in hot-climate regions like Iraq.

Construction Materials doi: 10.3390/constrmater5020039

Authors: Ramzi Abduallah Lisa Burris Jose Castro Halil Sezen

Incorporation of plastic waste into concrete mitigates harm to the environment through encapsulation of plastics in concrete. This study presents a comprehensive investigation of the effects of using six commonly used plastic materials (i.e., polyethylene terephthalate (PET), high-density polyethylene (HDPE), polyvinyl chloride (PVC), low-density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS)) in cement paste and mortar mixtures. The heat of hydration investigations revealed that plastic powders did not significantly affect rates or extents of hydration. Among the different types of plastic-aggregate mortars, PET performed the worst, while PS was the best. Fractures in the samples generally occurred due to debonding between the plastic particles and the cement matrix. Plastic particle shape influences the microstructure of the interfacial transition zone and consequently affects the overall strength of the mortar.

Construction Materials doi: 10.3390/constrmater5020038

Authors: Juan Zapata Doris Esenarro

This scientific research presents the most significant aspects of the structural analysis and verification of the main steel railway bridges in Peru in accordance with the American standard. To this end, linear and finite element analyses (FEMs) were performed using calculation notes in MATHCAD and structural validation software (SAP2000, CSI Bridge, IDEA STATICA and GE05), among others, based on on-site inspections, which allowed results to be obtained to analyze, evaluate and determine the structural performance factors (RF) of the main railway bridges in Peru. For this, data obtained from several railway corridors in Peru were taken into consideration, such as the lines of the Southern Railway Train, Central Andean Railway, Huancayo–Huancavelica Railway Train and the Tacna–Arica Train; in addition to the feasibility studies on the Interoceanic Train project: Iquitos–Yurimaguas; projects administered through Public–Private Partnership PPP as well as by the Regionals Government and MTC-Peru. These data were used in order to be able to warn of certain technical aspects that would influence the recommendations for a locomotive replacement project in which new units had different load distributions between the axles, which would make it necessary to review the tracks and bridges of the same in order to determine if they would be able to withstand the new forces safely, as well as to reinforce structural elements according to the material and the structural condition, and finally, to assess the variation in the increase in train speed in some road corridors to achieve a better FRA (Federal Railway Administration) classification of Class 3, where the presence of structures dating back to the last century has been verified as well (1851–1856–1908). Likewise, the seismic criteria and geotechnical conditions of the most representative areas of the country (acceleration 0.30 g) were included in order to also be able to make technical recommendations that would allow us to ensure the useful life of the structure in service, operation and maintenance conditions.

Construction Materials doi: 10.3390/constrmater5020037

Authors: Marco Antonio Sánchez-Burgos Begoña Blandón-González Esperanza Conradi-Galnares Paula Porras-Pereira Pilar Mercader-Moyano

Nanomaterials have emerged as versatile components revolutionizing diverse industries, yet their environmental and health impacts remain insufficiently explored. This paper delves into the latent hazards accompanying their evolution and integration, particularly within the construction sector. It addresses the critical gap in assessing their life-cycle impacts, emphasizing the necessity of explicit reporting on nanoparticle emissions. Employing a Life Cycle Assessment (LCA) approach, this research evaluates the sustainability of nanomaterial applications. The absence of nanoparticle-specific data in existing product databases underscores the need for comprehensive life-cycle emission reporting. Since direct impact calculations remain unfeasible, incorporating predicted emissions and risk assessments into LCA studies is recommended. This study advocates for incorporating nanoparticle risk evaluations into LCA methodologies to enhance sustainability and environmental safety. By prioritizing precise emission data and predictive risk analysis, it advances nanomaterial environmental assessments, contributing to the responsible implementation of nanomaterials in construction.

Construction Materials doi: 10.3390/constrmater5020036

Authors: Sepehr Pashoutani Mohammadsajjad Roudsari Jinying Zhu

Ground Penetrating Radar (GPR) is widely used for assessing the deterioration of concrete bridge decks. GPR surveys generate large amounts of data in the form of B-scan images, which display rebar traces as hyperbolas. Accurate analysis of the GPR scans relies on the effective extraction of rebar locations and amplitudes. This paper presents two automated rebar detection algorithms based on Convolutional Neural Network (CNN) machine learning techniques. Two models are proposed: CNN-1 and CNN-2. CNN-1 was trained on raw GPR images to identify hyperbolas, while CNN-2 model used both raw and migrated GPR images for enhanced analysis. The models were evaluated using GPR data collected from three bridges with different overlay types. Performance was assessed through the visual comparison of the generated bridge amplitude maps against ground-truth data, as well as precision, recall, and F1-score metrics. The results demonstrate that CNN-2 outperforms CNN-1 in terms of accuracy and efficiency for rebar detection.

Construction Materials doi: 10.3390/constrmater5020035

Authors: Hossam F. Hassan Khalid Al-Shamsi Khalifa Al-Jabri Saba Al Amri

Ferrochrome (FeCr) slag is a by-product of high-carbon ferrochromium, which is used in the manufacturing of stainless steel. In this study, FeCr was evaluated as a replacement for natural aggregates in hot-mix asphalt (HMA) bituminous base and wearing course layers. Four mixes were designed according to the Superpave mix design procedure, one control and three mixes, with FeCr slag replacing coarse, fine, or total aggregate. FeCr slag exhibited higher angularity and surface roughness than natural aggregates, resulting in an increased number of voids in mineral aggregate (VMA) and increased binder content. Performance testing using dynamic modulus, finite element analysis, and rutting evaluation using the MEPDG rut model showed that rutting increased with increased slag content. However, mixes with coarse aggregate replacement performed better than those with fine aggregate replacement. TCLP testing indicated that the FeCr slag is environmentally safe. The heavy metal leachate content was well below regulatory limits. Economic analysis showed material cost savings of up to 44% and 4% in the bituminous base and wearing course layers, respectively. The findings support the use of FeCr slag as a coarse aggregate replacement in asphalt mixes, offering both environmental and economic benefits.

Construction Materials doi: 10.3390/constrmater5020034

Authors: Zhu Liu Shupeng Wen Jian Wang Yi Li Linqiang Mao Yang Yang Zhongquan Liu

The use of tunnel kiln firing in clay brick production offers a promising approach for disposing of Cl-containing solid waste, with lower chlorine (Cl) and heavy metal volatilization compared to cement kiln processes. However, the effects of Cl salts on brick properties and the volatilization mechanisms remain unclear. This study investigates the behaviors of NaCl, KCl, and CaCl2 during sintering. Adding 15 wt% Cl salts significantly alters pore structure, increasing water absorption by 80–100% and reducing compressive strength by 70–80%. At 1050 °C, 10.8–16.4% of Cl volatilizes mainly as HCl (g), 24.4–26.2% remains in original salt form, and over half is immobilized within the brick matrix. Thermodynamic and TG-MS analyses reveal Cl salts are stable below 800 °C but release HCl (g) at higher temperatures due to lower reaction energy barriers than Cl2 (g). Density functional theory (DFT) calculations show that H+ for HCl (g) formation primarily originates from water vapor (H2O), with organic decomposition having minimal effect. The presence of Cl salts promotes feldspar and silicate phase formation, enhancing densification but increasing porosity from HCl release. To reduce HCl emissions, a two-stage temperature control strategy is proposed: organic decomposition and moisture removal below 600 °C, followed by sintering at 800–1000 °C. This work clarifies the volatilization mechanisms of Cl salts and provides guidance for optimizing industrial brick production using Cl-containing waste.

Construction Materials doi: 10.3390/constrmater5020033

Authors: Kazi Naimul Hoque Francisco Presuel-Moreno

This study investigates the long-term corrosion behavior of reinforced concrete (RC) under accelerated chloride exposure for about 1600 days, using electrochemical methods like galvanostatic pulse (GP) testing. Two concrete mixes (T1 and T2), incorporating distinct supplementary cementitious materials (SCMs), were evaluated to determine their performance in aggressive environments. Specimens with varying reservoir lengths were exposed to a 10% NaCl solution (by weight), with electromigration applied to accelerate chloride transport. Electrochemical assessments, including measurements of rebar potential, concrete solution resistance, concrete polarization resistance, corrosion current, and mass loss, were conducted to monitor the degradation of embedded steel. The findings revealed that smaller reservoirs (2.5 cm) significantly restricted chloride and moisture penetration, reducing corrosion, while larger reservoirs (10 cm) resulted in greater exposure and higher corrosion activity. Additionally, T1 mixes (partial cement replacement with 20% fly ash and 50% slag) showed higher corrosion currents and mass loss, whereas T2 mixes (partial cement replacement with 20% fly ash and 8% silica fume) demonstrated enhanced matrix densification, reduced permeability, and superior durability. These results underscore the importance of mix design and exposure conditions in mitigating corrosion, providing critical insights for improving the longevity of RC structures in aggressive environments.

Construction Materials doi: 10.3390/constrmater5020032

Authors: Pierre Rossi

This paper presents a new approach for modeling macrocrack propagation in reinforced concrete structures under both static and dynamic loading conditions. The numerical modeling is based on (1) the use of a probabilistic semi-explicit cracking (PSEC) model for macrocrack propagation and (2) the use of a deterministic damage model for the bond between steel and concrete. Another distinctive feature of the proposed modeling approach is the exclusive use of linear volumetric finite elements, both for macrocrack propagation and for the concrete/steel bond. For the latter, a single layer of volume elements is used along the reinforcement bars. Furthermore, the paper details a methodology for incorporating strain rate effects into the bond model under dynamic loading. It also outlines procedures for identifying the parameters required for both the static and dynamic formulations of the proposed models.

Construction Materials doi: 10.3390/constrmater5020031

Authors: Mahmoud Hayek Youssef El Bitouri Kamal Bouarab Ammar Yahia

The advancement of modern concretes, such as printable concrete, fluid concrete with adapted rheology, and ultra-high-performance concrete, has increased the importance of understanding structural build-up in cement-based materials. This process, which describes the time-dependent evolution of rheological properties, is a key factor to ensure the stability of concrete by influencing segregation, bleeding, formwork pressure, numerical modeling, and multi-layer casting. As a result, the structural build-up of cementitious materials has become a significant area of research in recent years. The structural build-up of cement based-materials results from both a reversible part (thixotropic behavior), driven by colloidal interactions, and an irreversible part, caused by cement hydration and the formation of C-S-H bridges. Various experimental techniques have been developed to investigate these processes, with various factors affecting the thixotropic behavior and overall structural build-up of cement suspensions. This review provides a comprehensive analysis of the current understanding of structural build-up in cement pastes. It covers measurement methods and key influencing factors, including the water-to-binder ratio (w/b), admixtures, temperature, and supplementary cementitious materials (SCMs). By consolidating the existing knowledge and identifying research gaps, this review aims to contribute to the development of sustainable, high-performance cement-based materials suitable for modern construction techniques.

Construction Materials doi: 10.3390/constrmater5020030

Authors: Rosana M. R. Mol Marialaura H. Rosas Keoma D. C. e Silva Ricardo A. F. Peixoto

The construction industry generates approximately 45% of the world’s total waste, highlighting the need for sustainable solutions. This study investigates the incorporation of quartzite waste (QW) and fiberglass waste (FW) into the production of gypsum plasterboard to reduce its environmental impact while maintaining its structural performance. The optimum formulation (MQ-20) was determined by replacing 20% of the gypsum with QW, based on the observed free water loss and crystallization water. The physical, mechanical, and thermal properties of the reference and modified boards were evaluated. The results showed that the MQ-20 samples exhibited a 30% reduction in flexural strength compared to the reference, while still exceeding regulatory standards. In addition, the MQ-20 samples had a lower thermal conductivity (0.54 W/(m∙K)) than the reference (0.58 W/(m∙K)). Fire-resistance tests showed that the inclusion of QW and FW reduced the size and number of cracks, improving the structural stability of the plasterboard at high temperatures. This research demonstrates that the incorporation of industrial waste into plasterboard is a viable and environmentally friendly approach, providing both mechanical and thermal performance benefits. These findings provide a basis for future studies aimed at developing sustainable building materials with improved functional properties.