Search Results (1,442)

Recycled aggregate concrete (RAC) mix design requires simultaneous consideration of mechanical performance, environmental impacts, and economic costs, yet these objectives are often evaluated separately. This study developed an integrated framework combining machine-learning-based strength prediction, life-cycle assessment, life-cycle cost analysis, constrained three-objective optimization, and preference-sensitive decision analysis. Using 407 RAC mixtures, Optuna-tuned Random Forest, XGBoost, and LightGBM models were compared, and SHAP was applied for interpretation. LightGBM achieved the best test performance, with an R² of 0.8822, an RMSE of 4.0276 MPa, and an MAE of 2.8865 MPa. The water-to-cement ratio, sand ratio, and superplasticizer dosage were the three leading predictors, together accounting for 68.5% of the normalized SHAP importance. A 100-generation NSGA-II optimization produced 150 feasible Pareto solutions spanning 33.87–75.25 MPa in compressive strength, 456.80–616.38 CNY/m³ in life-cycle cost, and 248.84–395.00 kg CO₂e/m³ in net carbon emissions. Higher-strength solutions generally required more cement and lower water-to-cement and recycled aggregate replacement ratios. Equal-weight TOPSIS selected P006, whereas the SMAA–TOPSIS simulation identified P007 as the alternative with the highest first-rank acceptability of 35.92%. By treating compressive strength as an explicit objective rather than a predefined constraint, the framework maps the continuous strength–cost–carbon trade-off within a volumetrically feasible mix-design space and identifies preference-dependent RAC design strategies. Full article

This study investigates the shear behavior and failure mechanisms of innovative hybrid structural beams fabricated by filling pultruded glass fiber-reinforced polymer (GFRP) box sections with waste rubber-reinforced concrete (RuC). Environmentally friendly concrete was produced by replacing natural aggregate with recycled tire-rubber fibers at proportions of 0%, 5%, 10%, and 15%. Twelve hybrid beam specimens were tested to evaluate the synergistic effects of rubber content and stirrup spacings of 16, 20, and 27 cm on shear capacity, ductility, and crack propagation. The experimental results revealed that the reference specimen (S16-0%) exhibited the maximum shear capacity of 154.41 kN and a brittle failure mode, while an increase in rubber content to 15%, combined with wider stirrup spacing, significantly reduced this capacity to a minimum of 96.89 kN (S27-15%). However, the 5% rubber replacement ratio achieved an optimal performance balance by preserving sufficient load-carrying capacity while enhancing flexural deformation and ductility, particularly in specimens with 16 cm stirrup spacing. Damage analysis demonstrated that longitudinal splitting cracks initiated in the mid-span tension zone at the bottom of the pultruded profiles, with final localized damage concentrated at the geometric corners of the box section. Crucially, the outer pultruded GFRP profiles provided substantial structural confinement, effectively mitigating the strength loss associated with high rubber incorporation and controlling the progression of sudden brittle failure. These findings highlight that combining pultruded GFRP profiles and optimized RuC offers a structurally viable and sustainable solution for modern infrastructure applications. Full article

To promote construction waste recycling and develop sustainable pavement materials, this study utilized recycled aggregates (crushing value 7.8%) obtained from bridge demolition as a 100% replacement for natural aggregates in recycled pervious concrete. The research focused on investigating the influence of different aggregate gradations (single-sized 4.75–9.5 mm and binary-graded combinations: 4.75–9.5 + 16–31.5 mm, 2–5 + 13–26.5 mm) and different water-to-cement ratios (0.26, 0.27, 0.30) on the concrete properties. Tests on compressive strength, splitting tensile strength, and connected porosity revealed the following results: The strength of recycled pervious concrete was comparable to that of natural aggregate concrete, and strength decreased with increasing aggregate size. The optimal water-to-cement ratio varied with gradation: 0.27 for the single-sized 4.75–9.5 mm aggregate and 0.30 for the binary-graded combinations. Splitting tensile strength was generally low, showed insignificant growth from 7 d to 28 d, was sensitive to interfacial defects, and exhibited high data variability. Connected porosity was inversely proportional to compressive strength and decreased with increasing water-to-cement ratio. This study provides experimental evidence for optimizing the preparation of high-performance recycled pervious concrete using recycled aggregates. In addition, the influence of fiber type, dosage, and length was preliminarily examined through an orthogonal design. Full article

This study investigated the resistance of recycled aggregate concrete (RAC) to chloride penetration under freeze-thaw cycles using both numerical simulation and experimental validation. A five-phase mesoscale model of RAC was developed. The salt freeze-thaw test was conducted to validate the simulated values and explore the effects of different recycled coarse aggregate (RCA) substitution ratios, as well as varying dosages of fly ash and superfine fly ash, on chloride concentration in RAC. The experimental data showed satisfactory agreement with the simulated values, confirming the model’s validity. Additionally, the RCA volume fraction, interfacial transition zone (ITZ) thickness, and adhesive ratio of old mortar were analyzed using simulation. The variation patterns of compressive strength, relative dynamic elastic modulus, and mass loss of RAC also revealed the mechanisms by which RCA substitution ratio and the dosages of fly ash and superfine fly ash act under salt freeze-thaw conditions. This study provides guidance for enhancing the resistance of RAC to chloride penetration and its durability under freeze-thaw conditions. Full article

The use of recycled aggregate concrete (RAC) enables the valorization of construction waste and supports carbon-reduction strategies. However, long-term service-induced deterioration means that recycled aggregates and their interfacial transition zones inevitably contain defects, which severely restrict the safe application of RAC in load-bearing structures. Notably, although RAC reduces embodied carbon by recycling construction waste, steel tube manufacturing introduces an additional carbon footprint; such carbon trade-offs can be well compensated by the improved structural efficiency and extended service life of steel-confined concrete, achieving superior whole-life carbon benefits. In the present study, a steel-tube-confined recycled aggregate concrete (STCRC) composite system is proposed. Through designed external confinement, the stress state of the internal concrete is altered from uniaxial compression to triaxial compression, thereby enhancing its axial load-bearing capacity. Axial compression tests were performed on 36 short column specimens of steel-tube-confined concrete (STCC) composed of C30 aggregate concrete and Q235 steel tubes with three wall thicknesses (4.5 mm, 6 mm, 8 mm). Further parametric finite element analyses with 16 calculation cases were conducted to quantify the effects of higher concrete strength grades (C40 and C50) and of steel tube strength grades. The evolutionary characteristics of the load-displacement response, the axial stress–lateral strain relation, and the lateral strain–longitudinal strain were systematically investigated across various parameters. Test outcomes indicate that steel tube confinement significantly restrains lateral dilation of RAC and enhances its ductility and ultimate bearing capacity, with higher confinement efficiency observed for RAC than for natural aggregate concrete (NAC). Numerical results further identify the differing sensitivities of NAC and RAC to variations in tube wall thickness, steel yield strength, and concrete strength grade. Using combined experimental and numerical datasets, a peak stress modification factor is proposed, and a tailored stress–strain constitutive model for STCRC is developed and validated. The research findings provide theoretical guidance for the design of axially compressed short columns made of prefabricated recycled concrete. Full article

The construction sector relies heavily on virgin mineral resources and produces significant quantities of construction and demolition waste. This study examines crushed brick aggregate (CBA) as a volumetric substitute for natural river sand in micro-concrete at replacement levels of 0%, 25%, 50%, 75%, and 100%. Results show that increasing CBA content decreases consistency and flexural strength while increasing water absorption. However, compressive strength is maintained even at full replacement. One-way ANOVA demonstrated significant overall effects of CBA replacement level on all investigated properties. However, Tukey’s HSD comparisons indicated that not all adjacent replacement levels exhibited significant differences. Specifically, compressive strength at 25% and 50% replacement did not differ significantly from the reference mixture. A nominal resource-efficiency assessment based on the absolute-volume method and literature-derived density values indicates that, at 25% volumetric replacement, the mixture incorporates approximately 286.7 kg/m³ of CBA and saves 362.4 kg/m³ of natural sand while retaining 94.3% of the reference compressive strength. For Croatia’s estimated 8882 t of waste bricks in 2024, a maximum yield scenario suggests production of about 30,985 m³ of this mixture and natural sand savings of approximately 11,231 t. The 25% replacement level offers the most balanced outcome in terms of secondary resource utilisation, consistency, mechanical performance, and water absorption. Full article

Reliable prediction of the compressive strength of self-compacting concrete with recycled coarse aggregate (SCRCAC) from mixture composition supports more rational mix design and fewer experimental tests. Using the benchmark dataset of the reference study (603 mixtures, eight input variables), this work re-examines machine-learning prediction of this property with an emphasis on honest evaluation rather than on a new model. A stacking ensemble of three gradient-boosting models (XGBoost, LightGBM, CatBoost) and an extremely randomized trees model, combined through a ridge meta-learner, is used as a representative model and compared with the four machine-learning models of the reference study (Random Forest, Extra Trees, XGBoost, LightGBM), the recent single-booster model of Abood et al., and the reference artificial neural network. Reported as the mean over 25 repeated 70/30 splits, the ensemble reaches R² = 0.793 ± 0.038 and RMSE = 6.21 ± 0.48 MPa, above all four reference models (R² = 0.7249–0.7635) and significantly, though only marginally, above a tuned single XGBoost. The central contribution is the evaluation itself. Because the dataset contains repeated identical compositions, a leakage-free protocol lowers the R² of every model to between 0.60 and 0.71, showing that the values of about 0.81–0.87 usually reported are inflated by duplicate-composition leakage, and leave-one-source-out evaluation lowers it further to about 0.14. Mutual-information and partial-dependence analyses identify cement as the dominant predictor, with water acting mainly through a nonlinear dependence. Robust, leakage-aware evaluation, rather than model architecture, emerges as the key to credible strength prediction on this benchmark. Full article

This study investigated the underwater abrasion resistance of recycled aggregate concrete according to ASTM C1138 using recycled aggregates obtained from demolished concrete as a 100% replacement of natural aggregates. The objective was to reduce the consumption of natural resources and minimize construction and demolition waste. In addition, ground granulated blast furnace slag (BFS) was used as a supplementary cementitious material at replacement ratios of 25% and 50%. Three BFS products with Blaine fineness values of 3000, 4000, and 6000 cm²/g were used to investigate their effects on the compressive strength and underwater abrasion resistance of recycled aggregate concrete. The experimental results showed that the compressive strength of recycled aggregate concrete was approximately 7% lower than that of natural aggregate concrete. However, the underwater abrasion test according to ASTM C1138 showed that the abrasion depth of recycled aggregate concrete was comparable to that of natural aggregate concrete. After 72 h of testing, the abrasion depth of recycled aggregate concrete was only slightly higher than that of natural aggregate concrete. In contrast, recycled aggregate concrete exhibited a higher weight loss, with an average value of 2.10% compared with 1.77% for natural aggregate concrete. Among the BFS mixtures, increasing the Blaine fineness of BFS resulted in lower abrasion depth and lower mass loss. Concrete containing BFS6000 exhibited the best underwater abrasion resistance within the BFS mixtures, although all BFS mixtures showed higher abrasion depth and mass loss than recycled aggregate concrete without BFS. At the 25% replacement ratio, concrete containing BFS6000 exhibited the lowest abrasion depth (3.11 mm) and weight loss (3.37%), whereas concrete containing BFS3000 showed higher values. A similar trend was observed at the 50% replacement ratio, although both abrasion depth and weight loss slightly increased compared with the corresponding 25% mixtures. The results demonstrate that recycled aggregate concrete combined with BFS has good potential for hydraulic structures and other concrete structures exposed to underwater abrasion. Although a slight reduction in compressive strength was observed, the underwater abrasion resistance can be improved by using BFS with higher Blaine fineness together with quality-controlled recycled aggregates. These findings provide useful information for the development of sustainable recycled aggregate concrete and support the efficient utilization of recycled materials in hydraulic engineering applications. Full article

To promote the high-value utilization of construction and demolition waste in cementitious materials, this study proposed an integrated strengthening strategy combining recycled coarse aggregate modification with cementitious matrix optimization. Recycled coarse aggregates with particle sizes of 4.75–31.5 mm were prepared from demolished concrete waste collected in Aksu, Xinjiang, China, and treated by particle shaping, alkaline solutions, and polyvinyl alcohol (PVA). Silica fume and a polycarboxylate superplasticizer were used to optimize the cementitious matrix. The physical properties of recycled aggregates, the mechanical performance of recycled aggregate concrete, and the mechanical and durability performance of high-content recycled aggregate cement-stabilized materials were evaluated. Particle shaping reduced water absorption and the crushing index from 6.8% and 14.4% to 5.6% and 12.6%, respectively. After treatment with 5% NaOH and 10% PVA, the apparent density increased to 2779 kg/m³, whereas water absorption and the crushing index decreased to 3.3% and 8.3%, meeting Class II recycled coarse aggregate requirements. With 10% silica fume and 0.2% superplasticizer, the 28-day compressive strength of recycled aggregate concrete prepared with the optimized aggregate and matrix reached 27.6 MPa, corresponding to 97.5% of that of natural aggregate concrete. The combined modification approach improved mechanical performance and reduced drying shrinkage, but the replacement ratio should be limited to 60% to satisfy the F50 freeze–thaw requirement under the tested conditions. Full article

The reuse of the finest fraction derived from recycled aggregate washing has been investigated for the manufacture of mortars. This practice contributes to the circular economy and lowers CO₂ emissions in the manufacturing of construction materials. A distinction was made between concrete-rich residues (RH) and mixed concrete–ceramic wastes (RHM). Chemical and mineralogical analyses of samples collected over a two-year period revealed consistent homogeneity over time. The RH residues are richer in CaO, primarily as calcite. Conversely, higher ceramic content in the waste correlates with increased SiO₂, Al₂O₃, and K₂O concentrations, predominantly as phyllosilicates and feldspars. Ettringite and portlandite occur in trace amounts. DTA-TG analysis reveals the presence of minor contents of portlandite and C-S-H gel. Mortars were prepared by replacing 10%, 20%, and 30% of Portland cement (OPC) with concrete-derived (RH) and mixed concrete–ceramic (RHM) wastes. At 10% and 20% substitution, both wastes yielded similar strengths, confirming their high potential for masonry mortars without prior treatment. However, at 30% replacement, RH provided markedly higher compressive and flexural strengths than RHM, likely due to a greater presence of the C-S-H gel phase in concrete waste. While 10% and 20% replacements successfully meet the 70% Strength Activity Index (SAI) threshold, a 30% limit severely reduces strength. Consequently, substitutions of 30% or higher require mechanical or thermal activation to enhance CDW reactivity. Given the minimal performance gap between RH and RHM, processing mixed CDW streams uniformly is recommended to maximize economic viability and ensure batch homogeneity in industrial washing plants. Full article

Recycled aggregate concrete (RAC) offers an effective approach to reducing the environmental burden associated with construction and demolition waste. In this study, a fiber-reinforced RAC was developed by replacing part of the cement with fly ash and ground granulated blast-furnace slag, while glass fibers or basalt fibers were incorporated as reinforcing materials. A systematic experimental program was conducted to evaluate the mechanical behavior of the proposed concrete under different saturation conditions. The results show that the best toughness performance was achieved in the natural moisture state. In comparison, compressive and flexural strengths reached their maximum values under dry conditions, whereas splitting tensile strength peaked in the natural state. Based on the experimental data, prediction equations were established for the splitting tensile and flexural strengths by considering both saturation degree and fiber content. A stress–strain model under uniaxial compression was also developed. In addition, scanning electron microscopy (SEM) was employed to examine the fiber–matrix interface and hydration products, thereby clarifying the microstructural characteristics of the concrete at different saturation levels. Full article

Construction and demolition waste remains a major sustainability challenge, while the use of mixed recycled aggregates in structural concrete is still limited due to concerns over variability, water absorption, and durability. This study investigates whether washed mixed recycled coarse aggregate can partially or fully replace natural coarse aggregate in concrete for seawall block applications. The recycled aggregate was characterized and then upgraded through simple washing and grading to remove fines and contaminants. Concrete mixes incorporating 0%, 5%, 1780, 20%, 50%, and 100% recycled aggregate replacement were produced and tested for workability, compressive strength, flexural strength, density, and water absorption under both tap-water and saline curing conditions. The results demonstrate that washing significantly improves aggregate quality, enabling compressive strength comparable to the reference mix at replacement levels up to approximately 20%. Higher replacement levels led to reductions in workability, flexural strength, and density; however, performance remained within technically acceptable limits. Overall, the findings indicate that washed mixed recycled coarse aggregate is a viable material for seawall concrete, supporting more circular and sustainable use of construction and demolition waste in marine infrastructure. Full article

To address the weak interfacial transition zone and insufficient mechanical properties of recycled aggregate pervious concrete, this study proposes a dual modification strategy using basalt fibers and ultra-fine mineral powder. The macroscopic mechanical and hydraulic properties of the material were analyzed through orthogonal experiments. Techniques including X-ray diffraction, scanning electron microscopy, and micro-computed tomography were employed to systematically reveal the microstructural evolution and internal pore network topology of the modified system. Based on range analysis of mechanical stiffness and drainage efficiency, the optimal mix proportions were determined as 5–10 mm aggregate, a water–cement ratio of 0.31, and a fiber content of 0.50%. Microscopic tests confirm that the pozzolanic reaction of ultra-fine mineral powder increases matrix density and enhances the shear bond strength between fibers and the cement paste, enabling the physical bridging effect of basalt fibers. The dual modification exhibits a synergistic effect on load-bearing capacity and crack resistance. CT scan results show that the internal pore cross-sectional area follows a unimodal skewed distribution, with the characteristic distribution peak located at 3.5 mm². This homogeneous microporous network limits the critical defect size, optimizing the stress transfer path while ensuring fluid transport. Full article

The weak mechanical behavior of recycled aggregate concrete (RAC) stems from microstructural defects in its composition. This study investigates the reinforcement of RAC through steel fiber incorporation. Using RAC replacement ratios and steel fiber contents as variables, this study examined their effects on compressive strength, splitting tensile strength, elastic modulus, and Poisson’s ratio. The axial compressive stress–strain curves of steel-fiber-reinforced RAC specimens were systematically measured. Scanning electron microscopy was employed to elucidate the modification mechanisms of steel fibers in RAC. The findings indicate that although greater replacement ratios weaken the mechanical performance of steel-fiber-reinforced RAC, an increase in fiber dosage enhances its strength. The most significant enhancement occurs when fiber content increases from 0.5% to 1.0%; at a replacement ratio of 0, the splitting tensile strength achieves the highest improvement of 11.14%. By considering the influencing factors, including the replacement ratio and steel fiber content, mechanical performance indices such as cube compressive strength were determined. Furthermore, the quantitative correlations linking the transformed values of various indices and the governing variables, together with the complete stress–strain curve formulations, were developed. The enhancement in RAC performance can be ascribed to the crack-bridging and crack-resisting effects provided by the embedded steel fibers. This research provides crucial experimental evidence supporting the engineering applications of steel-fiber-reinforced RAC. This study offers essential empirical data that underpin the practical implementation of steel-fiber-enhanced RAC. Full article

Mechanistic simulation and machine learning are powerful but complementary tools: physics-based simulation is interpretable yet computationally expensive and blind to real-world context, whereas machine learning is fast but data-hungry and opaque. Biological systems resolve this tension elegantly, coupling physically grounded mechanoreceptor sensing with higher-level neural interpretation that places those signals in context. Inspired by this layered architecture, we present Mechanics-AI, an open-source framework that mirrors the same sensing-then-interpretation logic computationally. A first learning layer (ML1) emulates expensive finite-element, computational fluid dynamics and multiphysics simulations to produce interpretable physical metrics such as stress, strain, shear, and thermal and moisture fields, while a second layer (ML2) fuses these metrics with heterogeneous real-world metadata to predict categorical outcomes and design recommendations. Eight algorithms are benchmarked automatically, the most accurate is selected for each task, and Shapley additive explanations expose the dominant physical drivers to preserve interpretability. The framework is demonstrated across three independent domains using a single unchanged pipeline: forensic traumatic brain injury prediction, optimisation of a bio-inspired humanoid bioreactor for tissue engineering, and a zero-emission building (ZEBAI) framework that couples thermo-hygro-mechanical simulation with Sobol-sampled surrogate modelling to design sustainable, low-carbon envelopes from recycled aggregate concrete by balancing structural safety, energy and embodied carbon. Despite entirely different physics, data and objectives, the same architecture generalises across all three, showing that bio-inspired, layered coupling of mechanistic simulation and contextual learning offers a reusable, interpretable route to cross-domain engineering prediction and sustainable design. Full article