Search Results (406)

Damping has attracted increasing attention as an indicator for structural health monitoring (SHM), owing to its sensitivity to subtle damage that may not be reflected in natural frequencies. However, the practical application of damping-based SHM remains limited by the accuracy and robustness of damping identification methods. Enhanced Frequency Domain Decomposition (EFDD), a widely used operational modal analysis technique, offers efficiency and user-friendliness, but suffers from intrinsic deficiencies in damping identification due to bias introduced at several signal-processing stages. This study proposes to improve EFDD by integrating neural networks, replacing heuristic parameter choices with data-driven modules. Two strategies are explored: a step-wise embedding of neural modules into the EFDD workflow, and an end-to-end grid-weight framework that aggregates candidate damping estimates using a lightweight multilayer perceptron. Both approaches are validated through numerical simulations on synthetic response datasets. Their applicability was further validated through shaking-table experiments on an eight-storey steel frame and a five-storey steel–concrete hybrid structure. The proposed grid-weight EFDD demonstrated superior robustness and sensitivity in capturing early-stage damping variations, confirming its potential for practical SHM applications. The findings also revealed that the effectiveness of damping-based indicators is strongly influenced by the structural material system. This study highlights the feasibility of integrating neural network training into EFDD to replace human heuristics, thereby improving the reliability and interpretability of damping-based damage detection. Full article

Cold-bonded (CB) fly ash aggregate, an eco-friendly material derived from industrial by-products, is used to fully replace natural coarse aggregate in producing lightweight concrete (LWC-CB). This study systematically investigates the post-high-temperature mechanical properties and damage mechanisms of LWC-CB. Specimens exposed to ambient temperature (10 °C) and elevated temperatures (200 °C, 400 °C, 600 °C) underwent cubic compression tests, with surface deformation monitored via digital image correlation (DIC). Experimental results indicate that the strength retention of LWC-CB is approximately 6% superior to ordinary concrete below 500 °C, beyond which its performance converges. Damage analysis reveals a transition in failure mode: at ambient temperature, shear failure is governed by the low intrinsic strength of CB aggregates, while after high-temperature exposure, damage localizes within the mortar and the interfacial transition zone (ITZ) due to mortar micro-cracking and thermal mismatch. To elucidate these mechanisms, a three-dimensional mesoscale model was developed and validated, effectively characterizing the internal multiphase structure at room temperature. Furthermore, a homogenization model was established to analyze the macroscopic thermo-mechanical response. The numerical simulations show strong agreement with experimental data, with a maximum deviation of 15% at 10 °C and 3% after high-temperature exposure, confirming the model’s accuracy in capturing the performance evolution of LWC-CB. Full article

Wet–dry cycles are a key factor aggravating the durability degradation of foam concrete. To address this issue, this study prepared bentonite slurry–steel slag foam concrete (with steel slag and cement as main raw materials, and bentonite slurry as admixture) using the physical foaming method. Based on 7-day unconfined compressive strength tests with different mix proportions, the optimal mix proportion was determined as follows: mass ratio of bentonite to water 1:15, steel slag content 10%, and mass fraction of bentonite slurry 5%. Based on this optimal mix proportion, dry–wet cycle tests were carried out in both water and salt solution environments to systematically analyze the improvement effect of steel slag and bentonite slurry on the durability of foam concrete. The results show the following: steel slag can act as fine aggregate to play a skeleton role; after fully mixing with cement paste, it wraps the outer wall of foam, which not only reduces foam breakage but also inhibits the formation of large pores inside the specimen; bentonite slurry can densify the interface transition zone, improve the toughness of foam concrete, and inhibit the initiation and propagation of matrix cracks during the dry–wet cycle process; the composite addition of the two can significantly enhance the water erosion resistance and salt solution erosion resistance of foam concrete. The dry–wet cycle in the salt solution environment causes more severe erosion damage to foam concrete. The main reason is that, after chloride ions invade the cement matrix, they erode hydration products and generate expansive substances, thereby aggravating the matrix damage. Scanning Electron Microscopy (SEM) analysis shows that, whether in water environment or salt solution environment, the fractal dimension of foam concrete decreased slightly with an increasing number of wet–dry cycle times. Based on fractal theory, this study established a compressive strength–porosity prediction model and a dense concrete compressive strength–dry–wet cycle times prediction model, and both models were validated against experimental data from other researchers. The research results can provide technical support for the development of durable foam concrete in harsh environments and the high-value utilization of steel slag solid waste, and are applicable to civil engineering lightweight porous material application scenarios requiring resistance to dry–wet cycle erosion, such as wall bodies and subgrade filling. Full article

Basalt fiber (BF) can notably improve the mechanical properties of lightweight aggregate concrete (LWAC) through its crack-bridging and pull-out mechanisms, making it suitable for application in super high-rise buildings and large-span structures. This study assesses the influence of BF contents of 0%, 0.1%, 0.3%, 0.5%, and 0.7% (relative to the weight of cementitious materials) on the workability, mechanical properties, and microstructure of LWAC. The results showed that adding BF to LWAC can moderately weaken the slump, significantly enhance the mechanical properties, and lead to a maximum increase in specific strength of 7.3%. Compared with LWAC without BF, the maximum increases in compressive strength, flexural strength, and elastic modulus of LWAC with BF at 28 days were 24.7%, 33.9%, and 38.57%, respectively. In the microstructure, BF can connect the cracks in the internal structure of concrete, which is an important factor to consider when choosing a fiber to improve the mechanical properties of concrete. These conclusions provide a reference point for improving the mechanical properties of LWAC. Full article

Three-dimensional concrete printing (3DCP) is advancing rapidly, yet its sustainable adoption requires alignment with circular-economy principles. This study evaluates the substitution of natural aggregates with recycled constituents, 3DCP waste, brick debris, glass cullet, mixed rubble, fly ash, and slag, and the use of lightweight fillers (expanded perlite, lightweight expanded clay aggregate (LECA), and expanded polystyrene (EPS)) to reduce density and improve insulation. Key properties, such as particle-size distribution, printability, mechanical performance, thermal conductivity, and water absorption, were determined. Results indicate that grading strongly affected mixture behavior. Narrow distributions (fly ash, milled 3DCP waste) enhanced extrudability, while broader gradings (glass, rubble, slag) increased water demand and extrusion risks. Despite these differences, all systems remained within the printable window: flow spread decreased with most recycled additions (lowest for brick) and increased with glass. Mechanical responses were composition-dependent. Flexural strength typically decreased. Compressive strength benefited from broader gradings, with replacement levels up to ~6% enhancing strength due to improved packing. Loading anisotropy typical of 3DCP was observed, with perpendicular compressive strength reaching up to 13% higher values than parallel loading. Lightweight fillers significantly reduced thermal conductivity. LECA provided the best compromise between strength and insulation, perlite showed intermediate behavior, and EPS achieved the lowest thermal conductivity but induced significant strength penalties due to weak matrix-EPS interfaces. Water absorption decreased in recycled-aggregate mixes, whereas lightweight systems, particularly with perlite, retained higher uptake. The results demonstrate that non-reactive recycled aggregates and lightweight insulating fillers can be successfully integrated into extrusion-based 3DCP without compromising printability. Full article

Growing concerns about industrial waste have intensified the search for practical reuse strategies in the construction industry. One of the most problematic types of waste is decommissioned wind turbine blades, which are tough, lightweight glass fibre composites that resist conventional recycling. In this study, shredded glass fibre-reinforced polymer (GFRP) recovered from such blades was used to partially replace the 2–8 mm fraction of natural aggregate in concrete at 10%, 20%, 30%, and 40% by volume. X-ray fluorescence (XRF) analysis showed that the material consists mainly of SiO₂, CaO, and Al₂O₃. X-ray computed tomography (XCT) revealed uneven fibre dispersion and a clear increase in porosity. Compared with the control mix, compressive strength reduced by 7–25%, splitting tensile strength by 18–24%, and elastic modulus by 17–35%. All mixes achieved watertightness class W12 (1.2 MPa), though the depth of water penetration increased with GFRP content. After 50 freeze–thaw cycles, frost-resistance class F50 was only met at 10% replacement. While these trends underline the performance trade-offs, they also point to a realistic route for diverting composite waste from landfills, reducing reliance on quarried aggregate and producing ‘green’ concretes for non-structural, prefabricated elements, where moderate strength is acceptable and reducing weight is advantageous. Full article

Due to the global growth of the construction industry, the use of concrete has increased rapidly. Consequently, the depletion of natural aggregates, which are essential components of concrete, has emerged as a critical issue. Simultaneously, the construction of marine structures has recently increased due to population growth and climate change. This trend highlights the growing demand for durable and sustainable construction materials in aggressive environments. To address the depletion of natural aggregates, extensive research has focused on artificial lightweight aggregates produced from industrial waste. However, the high porosity and low compressive strength of artificial lightweight aggregates have limited their effectiveness in ensuring the performance of sustainable marine structures. In this study, a high-performance mortar (HPM) incorporating artificial lightweight fine aggregates (ALWFAs) was developed to address the depletion of natural aggregates and to serve as a protective layer material in marine environments. To enhance the physical properties of ALWFAs, the aggregates were coated with epoxy-TiO₂ coatings applied to both their internal voids and external surfaces. The effectiveness of this enhancement was assessed by comparing the performance of mortars prepared with uncoated and coated ALWFAs. The HPM was evaluated for its porosity, compressive strength, split tensile strength, and chloride diffusion coefficient. The results showed that increases in the ALWFA replacement ratio led to a general reduction in performance. However, a comparison between uncoated and coated ALWFAs revealed that the coated aggregates led to improvements of up to 4.13%, 49.3%, 28.6%, and 52.0% in porosity, compressive strength, split tensile strength, and chloride diffusion coefficient, respectively. The study results are discussed in detail in the paper. Full article

Lightweight Aggregate Reinforced Concrete (LWARC) is increasingly used in structural systems to reduce dead load, especially in flat slabs. This study focuses on LWARC-incorporating polystyrene foam as a partial aggregate replacement, achieving a dry unit weight reduction from 23.0 kN/m³ to 19.0 kN/m³. While beneficial for lowering dead loads, this substitution exacerbates punching shear vulnerability, necessitating innovative strengthening solutions. Fiber-Reinforced Polymers (FRPs), recognized for their high strength-to-weight ratio, corrosion resistance, and adaptability, are employed to address these limitations. This paper evaluates the punching shear strengthening of LWARC flat slabs using externally bonded carbon fiber-reinforced polymer (CFRP) sheets, embedded through-section (ETS) steel bars, and ETS glass fiber-reinforced polymer (GFRP) bars. Ten specimens were tested under concentric loading, including an unstrengthened control slab. Experimental results were compared with predictions from ECP 203-2023, ACI 318-19, and BS 8110 to assess code applicability. Strengthened specimens demonstrated significant improvements in punching capacity and ductility. The ETS steel bar technique increased punching strength by 41% compared to the control, while inclined reinforcement configurations outperformed vertical layouts by 24% due to optimized shear transfer. Full article

Foam concrete is examined for use as a lightweight aggregate in concrete for building slabs. Crushed foam concrete should substitute LECAs in areas where LECAs are inaccessible. Suitable foam concrete mixes with and without admixtures and fine aggregates (limestone, stone dust, and micro silica) are tested to determine the densities (approx. range 550–1100 kg/m³), compressive strengths (approx. 0–8 MPa), and crushing potential measures as Percentage Mass of Useful Material After Crushing (approx. 70–90%). A mixing technique is developed using high revolutions. Some mixes show potential by providing a combination of density below 800 kg/m³, an adequately high compressive strength to be handled (>1 MPa), a low cement content (below 300 kg/m³), and a sufficiently high level of larger fragments above 4 mm when crushed (>80%). The results show that oven curing and curing beyond one day do not have a significant benefit. The investigation shows potential for two mixes, though developing the desired mixes further and studying a more consistent industrialised crushing method is recommended. Full article

Lightweight aggregate concrete is known for its potential to decrease overall building load and cost. Aero Aggregates’ Aerolite is a foamed glass aggregate (FGA) available in seven different sizes which has the potential to replace normal weight aggregates to create lightweight concrete. This research analyzes the feasibility of using FGAs in optimized concrete mix designs and employing those designs in a full-scale building. Nine different mix designs were created using optimization methods, including the Tarantula Curve and 0.45 power chart, to determine the ideal aggregate proportions. All mixes were cast in 0.1 m diameter, 0.2 m tall cylinders and tested after 7 and 28 days to determine unit weight (density), compressive strength, and modulus of elasticity. After testing, the optimal design was identified as 65% coarse and 15% fine aggregates to be replaced with FGAs because it gave the best unit weight and compressive strength for structural lightweight concrete. The optimal concrete mix design was used to create an example building model in RAM Structural Systems to prove that FGA concrete can reduce cost, materials required, and carbon emissions on a larger scale. Full article

Fly ash, as the main solid waste of coal-fired power plants, is an environmental problem that needs to be solved due to its massive accumulation. The mechanical properties and optimization mechanism of lightweight aggregate concrete prepared by using new single-cylinder rotary kiln fly ash ceramic granules as aggregate were systematically investigated. Through orthogonal experimental design, combined with macro-mechanical testing and microscopic characterization techniques, the effects of cement admixture and ceramic granule admixture on the properties of concrete, such as compressive strength, split tensile strength, and modulus of elasticity, were analyzed, and the optimization scheme of key parameters was proposed. The results show that the new single rotary kiln fly ash ceramic particles significantly improve the mechanical properties of concrete by optimizing the porosity (water absorption ≤ 5%), and its 28-day compressive strength reaches 46~50.9 MPa, which is 53.3~69.7% higher than that of the ordinary ceramic concrete, and the apparent density is ≤1900 kg/m³, showing lightweight and high-strength characteristics. X-ray diffraction (XRD) analysis shows that the new ceramic grains form a more uniform, dense structure through the synergistic effect of internal mullite crystals and dense glass phase; computed tomography (CT) scanning shows that the total volume rate of cracks of the new ceramic concrete was reduced by up to 63.8% compared with that of ordinary ceramic concrete. This study provides technical support for the utilization of fly ash resources, and the prepared vitrified concrete meets the demand of green building while reducing structural deadweight (20~30%), which has significant environmental and economic benefits. Full article

All-lightweight concrete (ALWC), using non-sintered fly ash ceramic pellets and pottery sand as coarse and fine aggregates, is a novel energy-efficient and environmentally friendly building material that has emerged in recent years. However, its structural behavior under impact loading remains to be thoroughly studied. This paper examines the dynamic response of four ALWC columns with different longitudinal reinforcement ratios and stirrup ratios under lateral impact loading using drop hammer tests. The effect of stirrup densification on the impact resistance was analyzed, focusing on the failure modes, impact forces, acceleration, and midspan displacement time history curves. Results showed that increasing the reinforcement and stirrup ratios shifted the column failure mode from shear to flexural failure, significantly enhancing peak impact force and reducing both midspan and residual displacements. Densifying the stirrups in the column ends resulted in localized flexural failure, with first and second peak forces increasing by 7.43% and 55.98%, respectively, thereby improving impact energy absorption and reducing impact damage. Full article

The article presents a recognition of the current state of the art in the field of bridge structures made using concrete on lightweight aggregate. The article aims to show the reader why aggregate with low mechanical parameters and high absorption can be used in demanding bridge constructions. Divided into two parts, the first presents the history of both topics and compiles the parameters of currently used lightweight aggregates by considering the guidelines applicable in the EU, China, and America concerning bridge construction. The literature review conducted highlighted both the advantages and disadvantages of using lightweight aggregates, presented the knowledge accumulated to date in this area, and identified important research gaps regarding lightweight aggregates. The second part discusses existing or planned bridge structures, taking into account their shapes and material properties. In summary, the challenges involved in the development of lightweight aggregate for bridge structures. The results obtained from the analysis will provide a basis for further research into the development of original lightweight aggregate for bridge structures. Full article

This study addresses the use of porcelain polishing waste as a pyro-expansive agent in clay-based formulations for the production of lightweight aggregates, aiming to reduce the consumption of natural resources and mitigate environmental impacts. In line with circular economy principles and sustainable construction goals, this study investigates the potential use of porcelain polishing waste as a pyro-expansive agent in clay-based formulations for producing sustainable lightweight aggregates. Using the Taguchi method and ANOVA, the effects of key processing parameters were evaluated. The results demonstrated a broad range of volumetric changes, from shrinkage of 40.84% to expansion of 91.69%, depending on the formulation and processing conditions. The aggregates exhibited specific mass values ranging from 0.99 g/cm³ to 2.36 g/cm³, water absorption up to 3.29%, and mechanical strength from 4.57 MPa to 39.87 MPa. Notably, nine of the sixteen experimental conditions met the technical standards for classification as LWA, indicating suitability for applications in high-strength, structural, and non-structural lightweight concretes, as well as lightweight mortars. The performance of these materials was directly linked to the chemical and mineralogical characteristics of the precursors and the proportion of pyro-expansive waste used. Overall, the findings suggest that 50% of the produced aggregates are viable for high-performance concrete applications, offering an environmentally responsible alternative to virgin raw materials and contributing to sustainable waste valorization in the ceramic and construction industries. Full article

The interfacial transition zone (ITZ) significantly influences the mechanical properties and durability of lightweight aggregate concrete (LWAC), yet existing research on the ITZ in LWAC remains fragmented due to varied characterization techniques, inconsistent definitions of ITZ thickness and porosity, and the absence of standardized performance metrics. This review focuses primarily on structural LWAC produced with artificial and natural lightweight aggregates, with intended applications in high-performance civil engineering structures. This review systematically analyzes the microstructure, composition, and physical properties of the ITZ, including porosity, microhardness, and hydration product distribution. Quantitative data from recent studies are highlighted—for instance, incorporating 3% nano-silica increased ITZ bond strength by 134.12% at 3 days and 108.54% at 28 days, while using 10% metakaolin enhanced 28-day compressive strength by 24.6% and reduced chloride diffusion by 81.9%. The review categorizes current ITZ enhancement strategies such as mineral admixtures, nanomaterials, surface coatings, and aggregate pretreatment methods, evaluating their mechanisms, effectiveness, and limitations. By identifying key trends and research gaps—particularly the lack of predictive models and standardized characterization methods—this review aims to synthesize key findings and identify knowledge gaps to support future material design in LWAC. Full article