Search Results (430)

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. Full article

Porous vegetated concrete has been widely used in highway slope protection because it provides both engineering stability and ecological restoration benefits. However, its life-cycle carbon emissions and long-term carbon sequestration performance have not been systematically quantified within a unified evaluation framework. In this study, 1 m³ of porous vegetated concrete was adopted as the functional unit, and a life-cycle assessment framework integrating carbon emissions and carbon sequestration was established. The results show that the material production stage is the dominant source of life-cycle carbon emissions, with cement consumption being the primary controlling factor. Under the system boundary and carbon sequestration assumptions adopted in this study, cumulative carbon sequestration over a 50-year service period was estimated to be approximately 470–475 kgCO₂eq. This exceeded the corresponding life-cycle carbon emissions of 73–124 kgCO₂eq and resulted in a net carbon sink potential of approximately 351–397 kgCO₂eq. Based on equal weighting of 28-day shear strength and material production-stage carbon emissions, the efficacy coefficient method identified M2 as the preferred mix proportion for balancing mechanical performance and low-carbon objectives within the selected evaluation framework. Monte Carlo simulation confirmed the statistical stability of the estimated mean carbon emissions during the material production stage. Sensitivity analysis further showed that cement-related emissions and the vegetation carbon sequestration factor were the two most influential parameters affecting life-cycle carbon performance. Overall, this study provides a quantitative basis for evaluating the net carbon sink potential of porous vegetated concrete and offers decision support for low-carbon mix design in highway slope ecological protection engineering. Full article

Coal gangue, a by-product of coal mining, has attracted increasing attention as an alternative aggregate in concrete because it can reduce natural aggregate consumption and promote solid-waste utilization. However, its porous, heterogeneous, and source-dependent nature often leads to weak interfacial bonding, reduced strength, and poor durability. Fiber reinforcement has been widely investigated as an effective strategy to compensate for these deficiencies, but the reported results remain scattered because of differences in gangue source, replacement level, fiber type and dosage, and test methods. This review systematically synthesizes the effects of fiber reinforcement on the mechanical performance, durability, and sustainability of coal gangue concrete. Reported results are comparatively analyzed as functions of coal gangue replacement level and fiber dosage. Two strength-normalized sustainability indicators, namely the Cost Coefficient Index (CCI) and Carbon Emission Index (CEI), are further introduced to compare the economic and environmental efficiency of different mixtures. Relatively favorable overall performance was most frequently reported within the commonly reported coal gangue replacement range for coarse aggregates, about 35–70%, with steel fiber and basalt fiber commonly showing favorable intervals of about 0.8–1.0% and 0.12–0.15%, respectively; polypropylene fiber also appeared favorable at about 0.6–1.0%, although the supporting evidence is comparatively less extensive. Full article

This study examines how fly ash-modified self-compacting concrete (SCC) behaves during curing under real conditions, focusing on changes in temperature and heat during the first days. Unlike typical lab tests at steady temperatures, three settings were used to copy real-life conditions: summer, winter with heating, and winter without heating. Temperature changes were tracked with built-in temperature sensors. Concrete maturity was calculated using a standard method (the Freiesleben-Hansen and Pedersen approach in ASTM C1074). The results show that heat in the first 72 h affects the maturity and strength of the concrete. After 7 days, strengths were measured as 32.7 MPa in summer, 27.2 MPa in winter-heated, and 15.7 MPa in winter-unheated settings. Predictions of strength based on maturity closely matched the measured values, proving that this approach works well in real settings. Examining the concrete’s structure with SEM and XRD tools showed that fly ash alters how the concrete forms and becomes denser, while lower temperatures slow key reactions, making the material more porous. These results show why early heat control matters. The maturity approach helps reliably estimate in situ strength and guide mix design for real projects. Full article

This study aims to explore the feasibility of utilizing high-titanium slag sand (HTSS) as a sustainable alternative to quartz sand in ultra-high-performance concrete (UHPC). The results indicated that incorporating HTSS accelerated cement hydration, enhancing 7-d and 28-d compressive strengths by up to 42.1% and 33.1%, respectively. Notably, at a 100% replacement ratio, the mixture exhibits distinct strain-hardening behavior with uniaxial tensile strength exceeding 6 MPa. Concurrently, autogenous shrinkage is reduced by 32% at 5 h and 68% at 7 d, while CO₂ emissions and energy consumption are lowered by 53 kg/m³ and 826 kJ/m³, respectively. Despite its rough and porous morphology, HTSS only marginally affects rheological properties. These findings provide theoretical insights into the development of low-carbon, low-shrinkage UHPC through the strategic valorization of industrial solid waste. Full article

Skid resistance is a critical functional property of asphalt pavements and is strongly influenced by surface topography. However, existing studies often rely on limited texture indicators, making it difficult to comprehensively characterize pavement surface morphology and directly relate it to braking performance. In this study, the surface topography of eight asphalt mixtures, including six porous asphalt concrete (PAC-13) mixtures with different air-void contents, one stone mastic asphalt (SMA-13) mixture, and one asphalt concrete (AC-13) mixture, was characterized using a high-precision three-dimensional laser scanner. The acquired point-cloud data were analyzed using one-dimensional, two-dimensional, three-dimensional, and ISO 25178 surface parameters. Correlation analysis was first used to remove redundant indicators, and principal component analysis was then performed to reduce dimensionality. Three principal components explaining 67.45%, 9.94%, and 6.42% of the total variance, respectively, were extracted and combined into a comprehensive surface topography index (F). The results showed that F effectively distinguished different mixture types and PAC surfaces with different air-void levels. Field validation was further conducted on PAC, SMA, and AC pavements in Xi’an, China, and a regression model relating F to the braking distance from 60 km/h to 0 km/h (D60) was established, with an R² of 0.8864. The proposed index provides a multidimensional and practical approach for asphalt pavement surface characterization and offers a useful basis for skid-resistance evaluation and braking distance prediction. Full article

Geopolymer concretes are increasingly regarded as advanced construction materials for applications requiring high thermal and chemical resistance. This article is a continuation of previously published research and focuses on the mechanical behaviour of geopolymer concretes containing aggregates made of foamed geopolymers and lightweight mineral aggregates, such as expanded clay and perlite, intended for use in chimney flue components. The aim of the study was to determine the influence of lightweight aggregates on the relationship between thermal insulation and the strength parameters of geopolymer concretes intended for use at elevated temperatures. Foamed geopolymer aggregates were produced by a controlled chemical foaming process, followed by grinding to specific grain sizes, yielding highly porous aggregates with low thermal conductivity, reaching approximately 0.075–0.099 W/(m·K). These aggregates were used as lightweight fillers in geopolymer concretes based on class F fly ash activated with alkaline solutions. The resulting composites were designed to combine low density and high thermal insulation with adequate mechanical strength. The mechanical properties of the developed concretes were assessed on the basis of compressive strength tests on cubic specimens and tensile strength in beam bending tests, carried out in accordance with standards. The results presented confirm that the use of foamed geopolymer aggregates enables a simultaneous increase in thermal insulation and the design of ultra-lightweight structural elements with sufficient load-bearing capacity for chimney systems (including suspended ones). This combination of low thermal conductivity, reduced mass, and appropriate mechanical properties makes geopolymer concretes with lightweight mineral and geopolymer aggregates a promising alternative to traditional ceramic materials. Full article

Permeable pavements are increasingly integrated into urban environments as sustainable systems that enhance stormwater infiltration, mitigate runoff, and contribute to pollutant control. However, long-term accumulation of contaminants within their porous structure may impair hydraulic performance and environmental functionality, particularly regarding microplastics (MPs), an emerging pollutant of growing concern. This study investigates the five-year environmental performance of porous concrete pavement slabs operating under real urban conditions, focusing on infiltration capacity and retention of nutrients, suspended solids, and MPs. A dual methodology combining continuous on-site permeability monitoring with laboratory analyses of aged slabs was used to assess performance decline and recovery after maintenance. Results show a 48% reduction in infiltration over five years, while maintaining effective functionality, and a 42.5% recovery after pressure cleaning. Used slabs exhibited substantial pollutant accumulation relative to new slabs, including increases of +258% in COD, +123% in total phosphorus, +28% in total nitrogen, and +48% in suspended solids. MP abundance reached 10,272 ± 5829 MPs/m², 7.5 times higher than in new slabs, dominated by fibers (~70%) and polymers such as PE, PP, and PET. These findings highlight the pavement surface layer as both hydraulic infrastructure and contaminant sink supporting improved maintenance and sustainable urban stormwater management. Full article

With the requirement for reducing carbon footprint in engineering construction, porous vegetation concrete is increasingly receiving attention for use in completed slope restoration. Cemented soil is introduced after the completion of porous vegetation concrete stabilization and functions mainly as a revegetation substrate. An important consideration for cemented soil in this application is its ability to maintain strength and water stability and possess moisture retention capacity, without causing much increase in alkali release or diffusion. This present study investigated a newly developed twofold stabilization system involving both cement binders and organic waterborne epoxy resin to meet the requirements of synthetically enhancing slope stabilization and restoration. Changes in the unconfined compressive strength and water stability were analyzed, whilst mineralogical composition and microstructure characteristics were investigated. The results indicated that moderate incorporation of triethylenediamine (TETA)-cured epoxy resin (1–2% by soil mass) moderately reduced strength and increased water stability with controlled alkali release in cemented soil. Mineralogical and microstructural analysis revealed that TETA-cured epoxy resin retarded cement hydration and refined particle bonding, exhibiting less consolidated pore structure characteristics. The twofold stabilization was exceptional in enhancing structural stability exposed to repeated humidity variation, albeit it yielded increased strength reduction rate from <7% to 9–16% under UV irradiation. Potentials of calcium sulfoaluminate cement and Portland slag cement were also investigated. A pilot-scale vegetation trial with representative plant species gave general agreement with effects observed in the laboratory in alkali reduction and moisture retention. The results provided an ecological approach for better restoring completed slopes that were stabilized using porous vegetation concrete. Full article

Additive manufacturing of concrete offers reduced waste, faster construction, and design freedom, yet effective reinforcement integration remains a major challenge due to weak interlayer bonding and anisotropy. Most prior studies focus on vertical reinforcement, short fibers, or metallic systems, achieving modest flexural improvements (15–60%). This study evaluates horizontal continuous reinforcement using glass fiber mesh and two carbon fiber meshes (ARMO-mesh 200/200 and 500/500) integrated during 3D printing. The methods include extrusion-based printing of small (four-layer) and beam-like (eight-layer) specimens, both printed and cast, followed by three-point flexural and compression tests at 7 and 28 days under vertical and horizontal loading. The results show that ARMO-mesh 500/500 significantly enhances flexural strength—up to 100% over unreinforced controls (e.g., 24.4 kNm vs. 12.2 kNm in small specimens at 28 days) and ~60% over ARMO-mesh 200/200, while glass mesh provides only marginal gains (~12%). Carbon meshes also improve post-cracking toughness and apparent interlayer cohesion. A pronounced size effect reduces nominal strength in larger specimens. These findings demonstrate that wide-format porous carbon meshes offer a scalable, corrosion-resistant solution for load-bearing 3D-printed concrete elements, advancing automated digital construction. Full article

The urgent global need for sustainable infrastructure drives the demand for high-value buildings and waste removal. This paper studies the feasibility of using recycled foam concrete aggregate (FCA) as a substitute for natural coarse aggregate (NCA) in concrete and studies its impact on rheology, mechanical degradation, shear resistance, and the full-range replacement ratio (0–100). The experimental results show that the monotonic change in the workability of fresh concrete determines the lubrication threshold at 60% replacement, which is driven by the volume proportion effect. Beyond this value, capillary suction dominates, and the viscosity rises rapidly. From a mechanical perspective, the porous structure of FCA is conducive to “internal curing” so that moisture is released from the drying interface, but it also becomes a source of defects that change the fault topology. Specifically, the critical transition of the shear failure mode shifts from the debonding of the interface to the crushing of the cross-particle aggregate. At this time, the shear capacity decreases substantially, experiencing a reduction of 71.8% when completely replaced. There is a strong correlation between ultrasonic pulse velocity (UPV), rebound number, and compressive strength, and a multivariate nonlinear regression model (R² > 0.85) with non-destructive strength prediction is ultimately obtained. Based on the balance between mechanical capacity and resource cyclability, an optimal alternative zone of 20% to 40% is proposed. This work not only provides a mechanism for multi-scale coupling between pore structure and structural properties but also provides a data-driven method for the safety assessment of lightweight recycled aggregate concrete (RAC). Full article

Natural pumice can reduce the self-weight of concrete, but its high porosity, high water absorption, and weak interfacial bonding tend to limit the strength and durability of lightweight aggregate concrete. To address this issue, this study proposes a method for preparing and applying reinforced pumice lightweight aggregates, namely, using nano-SiO₂-modified fly ash to construct a nanocomposite material at the micro-interface for the reinforcement treatment of natural pumice aggregates, and reveals the mechanism by which this treatment enhances the performance of lightweight aggregate concrete. Through aggregate performance tests, compressive strength tests, XRD, SEM, and freeze–thaw cycle tests, the effects of the reinforced pumice aggregate on the performance of lightweight concrete were systematically investigated. The results show that after the reinforcement treatment, the water absorption of the pumice aggregate decreases by 17.6%, and the cylinder compressive strength increases by 34.3%. As the replacement ratio of reinforced pumice increases, both the early-age and later-age compressive strengths of the concrete continuously improve. When all the pumice aggregate is reinforced, the 3 d and 28 d compressive strengths increase by 35.1% and 33.44%, respectively. Meanwhile, the reinforced pumice effectively improves the interfacial bonding between the aggregate and the cement paste, reducing the width of the interfacial transition zone by 32%, enhancing the matrix compactness, and delaying crack propagation. The study demonstrates that the reinforced pumice aggregate possesses favorable characteristics, not only effectively improving the mechanical properties and freeze–thaw resistance of lightweight concrete but also providing a new technical pathway for the high-performance utilization of porous lightweight aggregates, offering a reference for the resource utilization of industrial solid waste and engineering applications in cold regions. Full article

In order to study the noise reduction performance of Porous Elastic Road Surface (PERS), the vibration noise and air pumping noise has been separated from the tire–road noise through the finite element numerical simulation method. The tire–road noise model among the tire, road and surface air has been constructed by coupling of acoustic waves. The characteristics of tire–road noise under the PERS, Porous Asphalt Concrete (PAC), and Asphalt Concrete (AC) pavements have been analyzed through the modelling. The tire–road noise has also been investigated through the noise field tests. The generating process, coupling characteristics, and noise reduction performance of the vibration noise and the pumping noise of PERS pavements has been revealed. The results show that the tire–road noise was mainly generated by the vibration noise under the vehicle speed below 80 km/h. The proportion of pumping noise gradually exceeds that of vibration noise under the vehicle speed greater than 90 km/h. And the pumping noise gradually played the major role in the tire–road noise, which also increased with the increasing of vehicle speed. Comparing with AC and PAC pavements, PERS pavement exhibited the obvious advantages in noise reduction. Additionally, the reliability of the tire–road noise model has been verified through the field noise tests. It is expected that this work will serve as a reference for future research on the mechanics of the generation of tire–road noise, and try to provided theoretical support for the application of PERS. Full article

Environmental concerns associated with the construction industry have drawn increasing attention worldwide. This study addresses the dual challenges of carbon emissions from cement production and construction waste disposal by developing and characterizing a fiber-modified geopolymer recycled aggregate porous concrete (GRAPC). An orthogonal experiment first optimized the GRAPC mix proportion (slag content = 40%, alkali modulus = 1.4, alkali content = 8%). Subsequently, the effects of coir, basalt, and steel fibers (0.25% and 0.5%) on its properties were investigated through laboratory experiments combined with scanning electron microscopy (SEM) analysis. The results show that steel fibers at 0.25% dosage enhanced compressive strength by approximately 25% due to their effective stress-bearing capacity. In contrast, 0.5% coir and basalt fibers reduced compressive strength by approximately 20.5% and 22.2%, respectively, due to low intrinsic strength and agglomeration. In addition, 0.25% coir and steel fibers increased effective porosity by 18.4% and 17.4%, respectively, owing to their uniform dispersion. All fibers promoted a more ductile-like failure mode, with coir fibers providing the best toughness improvement. This study elucidates how fiber type and dosage regulate the macro-properties and micro-mechanisms of GRAPC, providing a basis for designing sustainable eco-friendly concrete with great potential for non-primary load-bearing engineering fields. Full article

To address the limited drainage capacity of conventional porous asphalt pavements under high-intensity rainfall, this study proposes the use of epoxy-modified bitumen to develop a large-void porous asphalt concrete (LV-PAC) with a target air void content of 25%. This approach represents a novel application of epoxy-modified bitumen to enhance permeability in porous pavement systems. The LV-PAC exhibited improved high-temperature stability, permeability, and clogging recovery capability compared with a conventional high-viscosity porous asphalt concrete (HV-PAC), though its low-temperature deformation capacity was relatively lower. All evaluated performance indicators met the required specifications, highlighting the potential of epoxy-modified bitumen for use in large-void porous pavements pending further field validation. Full article