Crushed-compacted solidified sludge (CCSS) is a novel fill material produced by first chemically solidifying dredged sludge to a target strength, followed by crushing and compaction. A systematic investigation into the wet-dry durability of CCSS and the corresponding mitigation strategies is of great significance for its engineering application. In this study, CCSS specimens solidified with an industrial by-product-based curing agent (GCP, composing ground-granulated blast-furnace slag, calcium carbide slag, and phosphogypsum), as well as GCP combined with waste pulp fibers (WPF), were subjected to cyclic wetting and drying tests, with ordinary Portland cement (OPC)-solidified CCSS serving as a comparison. Variations in macroscopic appearance, mass and volume, unconfined compressive strength (UCS), splitting tensile strength (STS), deformation modulus (E 50 ), and fracture energy (W), along with microstructural evolution characterized by X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and low-field nuclear magnetic resonance (LF-NMR), were analyzed to elucidate the degradation behavior of GCP-CCSS and the reinforcing mechanisms of WPF under wet-dry cycling. Results showed that GCP-CCSS exhibited lower mass and volume losses than OPC-CCSS under wet-dry cycling, and these losses were further mitigated by the incorporation of WPF. Throughout the cycling process, the UCS, E 50 , STS, and W of GCP-CCSS remained obviously higher than those of OPC-CCSS, while both mechanical stability and fracture energy were effectively enhanced by fiber reinforcement. Microstructural analyses revealed that GCP-CCSS initially contained abundant C-(A)-S-H gel and ettringite (AFt), which partially dissolved and disintegrated after 10 cycles, resulting in pore structure coarsening. In contrast, the incorporation of WPF effectively delayed microcrack initiation and propagation by enveloping soil aggregates and redistributing stress through interfacial friction among fibers, soil particles, and hydration products, thereby mitigating the detrimental effects of wet-dry deterioration.

Steel Fiber Reinforced Self-Compacting Concrete (SFSCC) is an innovative material that integrates the self-compacting ability of SCC with the strength and durability benefits of steel fibers. This review examines the mix design, fresh and hardened properties, durability, and microstructural characteristics of SFSCC, highlighting its performance advantages and challenges. Fresh properties were assessed using slump flow, T500, L-box, V-funnel, J-ring, and U-box tests, ensuring compliance with self-compacting standards. Hardened properties were evaluated through compressive strength, split tensile strength, flexural strength, elastic modulus, bond strength, flexural toughness, and impact resistance tests. Durability was examined using ultrasonic pulse velocity (UPV), permeability, sorptivity, and sulfate resistance tests, while microstructural analysis was conducted using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Energy Dispersive Spectroscopy (EDS). Findings reveal that incorporating steel fibers enhances strength, ductility, and durability. Compressive strength increased by 10%–35%, tensile strength by 11%–113%, and flexural strength by 10%–80%, while impact resistance improved significantly, with crack impact energy increasing by up to 3433%. Durability tests indicated improved resistance to water penetration and sulfate exposure, with a 6%–59% reduction in permeability and minimal compressive strength loss of 8.6% after prolonged sulfate exposure. Microstructural analysis confirmed reduced porosity and stronger interfacial bonding, contributing to long-term performance. Despite these advantages, challenges remain in optimizing mix design, ensuring uniform fiber dispersion, and addressing long-term durability. Further research is needed to refine material composition and enhance the sustainability and structural efficiency of SFSCC in construction applications.

The impact of multi walled carbon nanotubes on the mechanical properties of polypropylene fibre reinforced concrete

Development and performance of ambient cured geopolymer concrete with low alkali activation for sustainable construction

This review paper presents a comprehensive assessment of previous research on the utilization of waste fine materials in concrete as sustainable alternatives to conventional cementitious materials. The reviewed studies primarily focus on silica fume, fly ash, and other industrial and agricultural by-products used as partial replacements for cement in concrete. The findings indicate that appropriate replacement levels can significantly improve compressive strength, split tensile strength, flexural strength, durability, and overall concrete performance while reducing cement consumption and environmental impact. Several researchers reported that the combined use of supplementary cementitious materials produces better results than individual replacements due to improved particle packing and pozzolanic reactions. The literature also highlights the importance of proper mix proportioning, curing conditions, and material compatibility in achieving optimum strength and workability. Particular attention is given to M25 grade concrete prepared with 100% crushed sand and modified with silica fume and fly ash, where enhanced mechanical properties and economic benefits have been reported. The reviewed studies demonstrate that waste fine material concrete can achieve strength levels comparable to higher-grade conventional concrete while promoting sustainable and cost-effective construction practices. This review provides a foundation for further investigation into the comparative performance of conventional concrete and concrete incorporating combined waste fine materials

This study involves an integrated approach to predict the mechanical properties of luffa fiber and marble dust- based concrete. It employs Artificial Neural Network (ANN) for mechanical properties prediction aiming for a higher accuracy than currently available models. The composite material used marble dust in the proportion 0-40% as fine aggregate replacement and luffa fiber in the proportion 0-2% as the natural reinforcement. Experimental results implied that the composite containing 20% marble dust and 1% luffa fiber exhibited greatest mechanical characteristics- Compressive strength of 34.5MPa, flexural strength of 6.2MPa and split tensile strength of 4.25MPa. This improvement was attributed to enhanced particle packing by marble dust and effective crack bridging by treated luffa fiber. A single multi-output feedforward multilayer perceptron (MLP) ANN consisting of two hidden layers of 64 and 32 neurons with ReLU activation functions and a three-neuron linear output layer was developed for simultaneously modelling the nonlinear interactions between the input variables and strength outputs. The model was trained on 70% of the dataset, with 15% for validation and 15% for testing. The ANN model was able to predict all three mechanical strength properties simultaneously with a high degree of accuracy as demonstrated by R² values of 0.89 (compressive strength), 0.94 (flexural strength), and 0.96 (split tensile strength) for the training data sets and small root mean square error (RMSE) values and negligible bias. The 100% a20 score indicated that all the samples from the predictions fell within ± 20% of the actual experimental values, demonstrating good robustness or generality. This research basically aims to address a major gap in the existing works by exploring the limited application of ANN in predicting the performance of hybrid sustainable concrete mixes incorporating both marble dust and plant-based fibers by developing a predictive model which is capable of capturing the complex interactions between multiple factors and enhancing the prediction efficiency, minimizing the dependency on extensive experimental investigations thereby promoting data driven evaluation of strength characteristics in sustainable concrete composites.

This study examines the mechanical and flexural fatigue behaviour of concrete with reclaimed asphalt pavement (RAP) aggregates with and without steel fibre reinforcement. The use of RAP as partial replacement for natural aggregates represents a sustainable solution for reduction of construction waste and saving of natural resources. Twenty concrete mixes were prepared with RAP replacement levels varying between 0 and 30% and steel fibre contents varying between 0 and 1.25% by volume. The experimental investigation comprised t evaluation of strength characteristics, stress-strain behaviour, and flexural fatigue performance. Results show that increase in RAP content leads to a gradual decrease in the strength of the concrete due to weaker interfacial transition zone formed between the RAP aggregates and the cementitious matrix. However, the addition of steel fibres significantly enhances the tensile and flexural properties; the optimum steel fibre dosage was found to be 1%. At this dosage the compressive toughness was significantly increased, and the split tensile and flexural strengths improved as much as 45% and 48%, respectively. Stress-strain behaviour of RAP-based fibre reinforced concrete under compression is described by a modified Saenz equation based stress-strain model. The results of flexural fatigue tests indicated that fibre reinforcement substantially improves the fatigue life and endurance limit of RAP-based concrete. Machine learning models based on random forest regression and gradient boosting regression were also developed for the prediction of mechanical properties with the highest predictive accuracy of the gradient boosting model (R2 = 0.96). The integrated experimental and machine learning framework developed in this study provides a preliminary proof-of-concept methodology for evaluation and optimization of sustainable RAP-based fibre reinforced concrete for pavement applications.

This study proposes a data-driven experimental decision framework to identify the most suitable sustainable supplementary materials for green concrete, aiming to reduce cement usage, industrial waste burden, and environmental impacts in the construction sector. It experimentally evaluates compressive strength, split tensile strength, flexural strength, and ultrasonic pulse velocity (UPV) of green concrete incorporating waste materials including silica fume, GGBS, metakaolin, granite dust, rice husk ash, ceramic waste, marble powder, coconut shell powder, plastic waste, and bottom ash. A hybrid methodology integrating Pearson correlation, Analytical Hierarchy Process (AHP), and k-means clustering was developed to capture complex interrelationships. Correlation-based dependency analysis was incorporated into AHP to generate objective performance weightages, where compressive strength was ranked highest (37%), followed by flexural strength (25%), UPV (22%), and split tensile strength (16%). K-means clustering then categorized materials into best and worst performance groups. The findings revealed silica fume as the most optimal and balanced material, achieving 48.5MPa compressive strength, 4.0MPa split tensile strength, 7.5MPa flexural strength, and 4400m/s UPV, indicating superior structural performance and durability potential. ANOVA confirmed strong statistical distinction between clusters (p < 0.0001), validating the robustness of the classification. The main contribution of this work lies in introducing a scalable machine-learning-assisted multi-criteria framework that objectively ranks sustainable cement replacement materials, enabling reliable selection for high-performance green concrete design.

Rapid urbanization and the growing demand for sustainable construction materials have encouraged the development of low-carbon alkali-activated concrete (AAC). This study investigates the utilization of finely burnt clay brick dust (BD) and waste foundry sand (WFS) as alternative fine aggregates in ambient-cured cement-free AAC. Natural river sand was replaced from 25 to 100% using BD and WFS to evaluate their influence on fresh, mechanical, and durability properties. The binder system consisted of Class-F fly ash and ground granulated blast furnace slag, activated using an 8M sodium-based alkaline solution with a constant solution-to-binder ratio of 0.50. Results indicated that incorporation of BD reduced compressive strength due to its porous structure and higher water absorption, with reductions of 18.3% and 24.2% at 28 and 90days, respectively, at full replacement. In contrast, WFS significantly enhanced the performance of AAC because of its micro-filler effect and improved particle packing. The optimum performance was achieved at 50% WFS replacement, where compressive strength increased by 41.5% and 21.5% at 28 and 90days, respectively, while split tensile and flexural strengths also improved considerably. Durability performance was substantially enhanced at the optimum WFS level, with reductions of 60.9% in chloride penetrability, 62.7% in carbonation depth, 45.7% in water permeability, and 42% in sorptivity compared to the control mix. Furthermore, the 50WFS mix exhibited superior resistance against acidic and sulfate environments. The findings demonstrate that WFS can effectively replace natural sand up to 50% in ambient-cured AAC, producing a sustainable and durable construction material, while BD can be utilized at moderate replacement levels for effective waste valorization.

The use of natural fibres in concrete manufacturing has garnered global attention as sustainable building materials are sought after to enhance performance, mitigate resource depletion, and minimise environmental impacts. This research investigates the physical and mechanical behaviours of Elaeis Guineensis midrib fibres (EGMF)-based concrete, comparing untreated and treated EGMF variants. EGMF samples were treated with 1-5% of Ca(OH)2 solution at 1% increments for 6, 12, and 24h, and the tensile strengths were examined. Physical (slump) and mechanical (compressive strength, split tensile strength, flexural strength, bond, and rupture modulus) tests were conducted on 20MPa characteristic strength, with EGMF replacing the total concrete volume at 0.5-2%, and tested after curing for 7, 28, and 56 days. The results demonstrated an optimum tensile strength for EGMF at 4% and 24h of Ca(OH)2 solution and treatment. The slump decreased by 1-5% as EGMF dosages increased from 0 to 2%. Incorporating treated EGMF enhances the compressive, split tensile, and flexural strengths of concrete at optimum contents of 0.5%, 0.5%, and 1%. After 28 days of curing, the bond strength and slab's modulus of rupture of treated EGMF-based concrete outperformed those of untreated EGMF by 25.93% and 9.79%. Hence, the use of treated EGMF as reinforcement in concrete manufacturing enhances its mechanical properties, promoting the production of high-quality concrete and facilitating sustainable, cleaner production.

The current work contributes to the protection of natural raw resources and reduces environmental effects by recycling plastic in sustainable construction techniques. By investigating the exact transition point from a strength reducer to a functional benefit of plastic waste in the production of lightweight concrete, using coarse aggregates versus fine aggregates separately under the same curing conditions. Recycled polyethene (PE) waste, produced through thermomechanical extrusion and pelletizing, was used as a partial replacement of coarse and fine aggregates at 2.5%, 7.5% and 15% by weight. Seven concrete mixes of M25 were cast and tested for compressive strength, splitting tensile strength, and absorption rate after 7 and 28 days of curing. Findings indicated that the highest workability was achieved by replacing 15% of plastic particles with coarse aggregate (about 135 mm), while 2.5% PW had the lowest workability (about 45 mm) by replacing fine aggregate. While the highest compressive strength was obtained with a 2.5% replacement of fine aggregate, reaching about 26.22 MPa. In contrast, it decreased more severely when reaching 15% by about 21.11 MPa, compared to replacing coarse aggregates with plastic particles by about 22.44 MPa. Furthermore, substituting sand with recycled plastic particles at 2.5% replacement level resulted in the best splitting tensile strength of 1.69 MPa. It is noted that substituting coarse aggregates reduced the density more than fine aggregates, with the peak reduction rate being 3.66% for cube specimens after replacing 15% of coarse aggregates at 28 days, making it the most efficient replacement for producing lightweight concrete. All replacement levels of sand increase absorption rates by 10.4% over coarse aggregate. Therefore, these results are highly transferable to field conditions for non-structural applications such as pedestrian pathways and paving blocks, provided that workability is optimized.

As is known, pervious concrete is commonly used in low-traffic-load applications. Therefore, pervious concrete is exposed to flexural loads throughout its economic life. To improve the flexural behavior of pervious concretes, fibers are the most common solution used by researchers. Hence, fiber dosages of 0.1%, 0.2%, and 0.3% (by volume of concrete) are selected for this study. The influence of increased cement content is also discussed. Single-sized limestone aggregates without any mineral admixture were used to produce pervious concretes. The mechanical and hydraulic properties of the pervious specimens were examined. Additionally, image analyses using both CT (Computed Tomography) and scanned sliced samples were conducted. In this study, the samples containing 0.3% polypropylene fiber by volume yielded the highest splitting tensile and flexural strength. Adding fiber reduced the porosity of the pervious concrete. Mixtures with the highest fiber content exhibited the lowest porosity and permeability coefficients. Also, the porosity obtained from image analyses correlates well with volumetric porosity results. The impact of fiber additives on the strength and permeability of pervious concrete has been explored only to a limited extent in existing literature. This study contributes original insights by assessing this impact through a comprehensive approach that examines mechanical, hydraulic, and microstructural aspects, utilizing both experimental methods and image analysis.

ABSTRACT Expansive soils exhibit high compressibility, swelling & shrinkage behaviour, moisture sensitivity, and low bearing capacity, often causing differential settlement and structural damage in pavements and foundations. Although lime and cement stabilization, their production generates significant carbon emissions. This study examines Soil-FeT geopolymer mixtures as a sustainable alternative for subgrade stabilization. Soil specimens were treated with binder contents of 10, 20 and 30%, activated using 6, 8 and 10 M alkaline solutions. Mechanical performance was evaluated through unconfined compressive strength (UCS), split tensile strength (STS), California bearing ratio (CBR), resilient modulus (MR), and hydraulic conductivity tests, while durability was evaluated through 12 wetting‒drying cycles. Geo-environmental performance was examined using leachibility, carbon emission, and energy consumption analyses. Results showed that specimens containing 10% binder activated at 10 M achieved optimum performance, with UCS increasing from 0.23 to 4.89 MPa for low-plastic soil and from 0.11 to 3.81 MPa for high-plastic soil. The soaked CBR values increased approximately 12- and 19-fold compared to untreated soils. Treated specimens exhibited durability, with mass loss below 10%, and satisified IRC subgrade requirements. Heavy metal concentrations remained below USEPA limits. Sustainability assessment indicated 82% lower CO2 emissions and 61% lower energy consumption than cement stabilization, confirming Soil-FeTgeopolymers as an eco-friendly stabilizer for applications.

This study evaluates the mechanical and durability properties of M40-grade concrete modified with ground granulated blast furnace slag (GGBS), fly ash, and carbon nanotubes (CNTs). The objective is to address the environmental and performance limitations of conventional concrete, which is heavily reliant on cement. Four concrete mixes were examined: M40 (control), M40 incorporating 40% GGBS, M40 containing 30% fly ash, and M40 with CNTs (0.01-0.15%). The mechanical properties compressive, split tensile, and flexural strength were tested at 3, 7, and 28days, while durability tests such as rapid chloride penetration and water permeability were also performed. The results showed that CNTs, particularly at 0.03-0.05% concentrations, significantly enhanced the concrete's performance, with compressive strength increasing by 56%, tensile strength by 20%, and flexural strength by 39%. Durability improved, with a 100% reduction in water permeability and a 34.56% reduction in chloride penetration. Microstructural analysis via SEM indicated matrix densification and better hydration product distribution at effective CNT dosages. XRD confirmed enhanced C-S-H formation, but higher CNT dosages led to clustering, which reduced efficiency. GGBS-modified concrete outperformed fly ash-modified concrete, and CNT-modified concrete showed the greatest improvements. These findings suggest that CNT-modified concrete is particularly suitable for precast U-drain systems, where enhanced early-age strength, reduced cracking, and improved durability against chloride ingress can improve the service life and performance of drainage infrastructure. This concrete mix shows strong potential for high-performance, sustainable construction.

The manufacture of cement contributes significantly to carbon dioxide (CO2) emissions into the atmosphere. The effects of mineral admixtures (iron dust, glass fines, metakaolin, and limestone fines) make them suitable for reducing carbon emissions as a replacement for cement. All mineral admixtures (MA) are byproducts of primary materials, and natural fiber is included. This study focuses on a sustainable material that does not compromise strength. This paper analyzes the properties of self-healing concrete developed using MA Bacillus tropicus and sisal fiber. Three different percentages of MA, 10%, 20%, and 30%, and 1% of sisal fiber were used by weight of cement. Bacteria were incorporated into the concrete using the direct addition method, in which the healing solution (a combination of a 1:9 bacterial-to-nutrient ratio) was added directly to the concrete. A total of five mixes of concrete control C0, bacterial control CB, 10% MA CB10, 20% MA CB20, and 30% MA CB30 were cast. Thus, 1% sisal fiber was constant for all mixes. The self-healing concrete's (SHC) performance was assessed through sorptivity, porosity, water absorption, acid resistance, crack-healing efficiency (CHE), compressive strength (CS), splitting tensile strength (STS), regain compressive strength (RCS), and microstructural morphology analysis. The economic and environmental benefits are evaluated. A comparative analysis of the experimental results showed positive results up to a 20% replacement after declination, but not to a level below the reference mix. Adding fiber significantly increases tensile strength, achieving a 3 to 13% improvement over the control mix, and supports bacterial survival within the concrete environment. Optimal concrete mixtures of 20% were suggested, and the specimens showed improvements of 15.45% in CS, 12.53% in STS, and 90.96% in RCS compared to control concrete specimens. The recovery ratio can exceed 80% for all mixes except the control specimen. The economic analyses identified reduced maintenance costs and lower carbon emissions. The microstructural analysis confirms the presence of bacteria, as well as calcium carbonate and calcite.

Cement manufacturing is a significant source of CO2 emissions in the world, with approximately 8% of the global emissions being due to cement manufacturing, mainly through clinker manufacturing. In order to reduce its environmental effects, this paper examines the use of silica fume (SF) and Alccofine (AF) as additional cementitious materials (SCMs) to improve the mechanical and durability characteristics of concrete. The first stage involved the addition of SF at 5, 7.5 and 10% replacement levels to establish the optimum dosage and the second stage involved the addition of AF at 5, 10 and 15% with the optimum SF content maintained. Mechanical properties such as compressive strength, flexural strength, and split tensile strength and durability properties such as water sorptivity and rapid chloride penetrability (RCP) were tested. The best combination of 7.5% SF and 10% AF was 34.7% increase in compressive strength, 16.1% increase in flexural strength and 16% increase in split tensile strength over the control mix. This blend showed a 43.7% decrease in water sorptivity and a 42.8% decrease in RCP in terms of durability, which is significant in terms of resistance to water ingress and chloride penetration. Compressive strength was well predicted by machine learning models, with the most significant variables being cement content and AF. Life cycle assessment (LCA) indicated that the optimum blend had a global warming potential that was reduced by a factor of about 10% relative to OPC. These findings indicate that the integration of SF and AF does not only improve the performance of concrete but also minimizes its environmental impact, which is a promising avenue to sustainable and high-performance construction materials.

The increasing demand for natural aggregate in concrete production, along with the increasing production of waste due to industries and constructions, has created concerns regarding resource depletion and environmental degradation. Utilization of wastes in concrete mixes is a very effective method to save the natural resources as well as construct environmentally friendly buildings. In this paper, the performance of M40 grade concrete is examined through the use of silica fume, quarry dust, and ceramic wastes as partial replacements of conventional materials. Quarry dust is used in place of fine aggregate, and ceramic waste is used in place of coarse aggregate. Silica fume content varies from 6% to 9%, replacement level for quarry dust ranges from 10% to 40%, and replacement level for ceramic waste changes from 10% to 40%. Properties of raw materials were determined by specific gravity and sieve analysis tests before mix design. Characteristics of fresh concrete were measured using slump tests, and those of hardened concrete were measured by compressive strength, split tensile strength, and flexural strength tests. The effect of quarry dust, ceramic waste, and silica fume additions was reflected on the behavior of the concrete mixtures in terms of both workability and compressive strength. In the range of the tested combinations, the best compressive strength, which was equal to 53.33 MPa, was attained for the combination of 6% silica fume, 10% quarry dust, and 10% ceramic waste. This level of compressive strength was higher than the required compressive strength for M40 concrete. It is clear that the increase in the strength properties could be contributed by better packing and densification of the concrete due to the effects of silica fume and finely graded quarry dust. Nevertheless, higher proportions of these additives had negative impacts on the strength of concrete because of the increase in void age and poor interfacial bond between aggregates and paste.

The increasing demand for eco-friendly construction materials has driven the adoption of supplementary cementitious materials such as fly ash (FA) and ground granulated blast furnace slag (GGBS), as they offer a lower carbon footprint and improved durability. Portland Slag Cement (PSC) has been introduced as a blended cement, but its slower hydration and delayed pozzolanic reaction reduce early-age strength, limiting structural applications. This study aims to overcome this limitation by incorporating hybrid fibers such as basalt fibers (BF) and recycled steel fibers (RSF) at volume fractions of 0%-0.75% to enhance the early-age mechanical performance of PSC concrete. Around 15 different concrete mixes (with fiber) were formulated along with 1 control mix (without fiber) and tested for their properties at 7, 14, and 28 days. It was found that the control mix exhibited lower early strength due to slower PSC hydration and a delayed pozzolanic reaction in fly ash. However, the inclusion of fibers significantly compensated for this weakness. At 7 days, compressive strength increased from 26.2MPa for Low-Carbon Slag Cement (LCSC), to a maximum of 32.3MPa for the hybrid mix LCSC11 (0.5% BF + 0.5% RSF), representing an improvement of about 23%. Similar synergistic improvements were observed in split tensile and flexural strengths, with 28-day values reaching 5.4MPa and 8.3MPa, respectively, for the optimum hybrid mix. The inclusion of 0.5% BF + 0.5% RSF (LCSC11) into the fly ash-modified PSC concrete exhibited enhanced durability properties, with a 26% reduction in water absorption rate, a 30% reduction in sorptivity, a 41% reduction in chloride ion ingress, and a 34% reduction in weight loss under acid exposure. The findings demonstrate that hybrid BF-RSF reinforcement effectively offsets the early-age strength deficiency of fly ash-modified PSC concrete while significantly enhancing its tensile and flexural performance.

Thermal power stations generate large amount of coal bottom ash (CBA), which is mostly disposed of in landfills, creating environmental hazards. At the same time, the continual use of natural aggregate in concrete is depleting resources. Present study aims to address both these issues by utilizing coal bottom ash as partial substitute to river sand and quarry sand at values between 0% and 100%. Experimental results indicate that workability decreases with increasing CBA contain. The mixes made using river sand (CBA1) had their compressive and split tensile strengths close to 5% of those of the control mixes for higher curing ages. In contrast, the mixes made using quarry sand (CBA2) had a compressive strength that was 6% to 25% less than that of the control mixes at the 28-day curing period depending on the percentage of CBA used, whereas there was a drop to around ± 0% to 7% after 180 days of curing. Among different models developed, effective prediction approach within the considered experimental dataset Gradient Boosting outperformed the other models, showing the highest accuracy (R² = 0.99) and also with the least number of prediction errors. The outcome of present research suggests that CBA may serve as a durable material and that advanced machine learning techniques might accurately forecast its strength.

The construction sector faces a dual imperative: managing the escalating volume of construction and demolition (C&amp;D) waste while simultaneously reducing reliance on quarried natural aggregates, both of which carry significant environmental costs. Recycled aggregate concrete (RAC) addresses this dual challenge by substituting demolished concrete debris for natural coarse aggregate; however, RAC is characterized by reduced compressive strength, elevated porosity, and inferior interfacial transition zone (ITZ) quality relative to natural aggregate concrete (NAC), limiting its deployment in structural applications. This investigation presents a systematic experimental programme in which M30-grade RAC employing 100% recycled coarse aggregate (RCA) replacement was reinforced with hybrid combinations of steel fibers (SF, 6 mm hooked-end) and glass fibers (GF, 3 mm alkali-resistant) at total volume fractions of 0+0% (M1 NAC control), 0.5%+0.5% (M2), 1.0%+1.0% (M3), and 1.5%+2.0% (M4). Compressive strength (3, 7, 14, 28 days), split tensile strength, flexural strength, and water absorption were evaluated by IS standards. Relative to the NAC control (M1: CS = 38.43 MPa), the 100% RCA M2 baseline exhibited a 21.7% reduction in compressive strength; however, hybrid fiber additions progressively recovered performance, with M4 achieving 35.40 MPa (−7.9% vs NAC control but +17.6% vs unfiber-reinforced RAC baseline). More significantly, split tensile and flexural strength showed increases of 55.7% and 50.6% above NAC control for M4, respectively, confirming that fiber bridging is disproportionately beneficial for tensiledominated failure modes. The mechanistic basis for these improvements lies in steel fiber crack-bridging arresting macrocrack propagation and glass fiber microcrack suppression refining the ITZ. To extend predictive capability, a multi-output artificial neural network (ANN) with a 6-12-8-12-5 architecture was developed and trained on an N = 190 experimental datasets compiled from this study and published literature. The ANN achieved R² values of 0.987, 0.983, and 0.979 for compressive, split tensile, and flexural strength, outperforming XGBoost, Random Forest, and SVR. SHAP analysis identified RCA replacement percentage, steel fiber content, and glass fiber content as the three dominant predictors, quantitatively confirming the physical mechanisms observed experimentally.