Construction Materials

Accurate prediction of concrete mechanical and deformation behavior remains one of the major challenges in materials engineering and science. This study presents results from structural and finite element (FE) modeling, providing a prediction of the stress–strain state of hardened cement paste and concrete. It proposes a two-step method: first, develop an FE model for hardened cement paste from the monofractional structural model; second, develop an FE model for concrete by integrating deformation characteristics derived from the hardened cement paste model and interfacial transition zone (ITZ) parameters, calculated by the authors’ method. This study involved: designing structural models of hardened cement paste and concrete, constructing FE models based on these structures, and validating them by comparison with experimental data. The simulations used monodisperse structural and tetrahedral hinge–rod finite element models. The novelty of the method is the combination of simplified monofractional structural models and ITZ volume calculation using parameters for structural density and relative sizes of elements, which allows for the design of an FE model of concrete integrated with an FE model of hardened cement paste. The results confirm the high accuracy of the developed models for each concrete class in the range from C16/20 to C55/67, with deformation deviations not exceeding 6% and strength deviations not exceeding 10%. The authors’ principles of FE modeling for hardened cement paste and concrete were established. Full article

Concrete is the most used construction material, but its long-term performance depends on durability. Although fly ash has been used as a supplementary cementitious material, the effects of its mechanical activation on the concrete durability require further investigation. This study evaluated the influence of replacing 30% of cement with natural Class F fly ash (NFA) and ground fly ash (GFA) in concrete with a water-to-binder ratio (w/b) of 0.62, using a mixture without fly ash (WFA) as reference. Mechanical activation was performed by milling the fly ash, followed by characterization through particle size analysis and X-ray diffraction. Concrete durability was assessed using electrical resistivity, ultrasonic pulse velocity (UPV), water absorption, porosity, rapid chloride permeability (RCPT), carbonation resistance, and compressive strength tests. Mechanical milling reduced and transformed the ash morphology from spherical to amorphous, while quartz and mullite remained the main crystalline phases. Compared with CNFA, CGFA exhibited up to 101% higher electrical resistivity, 39.6% greater resistance to chloride penetration, 10.8% improved carbonation resistance, 0.4% lower water absorption, and a 5.38% reduction in porosity, although compressive strength decreased by more than 20%. These results demonstrate that mechanically activated fly ash is a viable alternative for enhancing the concrete durability performance exposed to aggressive environments. Full article

The durability of alkali-activated materials (AAMs) in acidic environments is a key factor governing their suitability as sustainable alternatives to ordinary Portland cement (OPC). This study investigates the acid resistance of fly ash–slag alkali-activated mortars prepared with either seawater-based or distilled water-based activator solutions, thereby addressing the feasibility of substituting potable water in activator preparation. Eleven binder blends were tested, ranging from 100% fly ash (F100G0) to 100% ground granulated blast furnace slag (GGBS, F0G100) in 10% replacement increments, each prepared with both distilled-water (D-series) and seawater-based (M-series) activator solutions. Mortar cubes were exposed to hydrochloric acid (HCl) and sulphuric acid (H₂SO₄) after curing for 28, 60, 90, and 180 days. Durability was assessed through mass change, compressive strength retention, and ultrasonic pulse velocity (UPV), complemented by X-ray diffraction (XRD) analysis to elucidate mineralogical transformations. Results showed that acid resistance was governed primarily by binder composition: calcium-rich slag (C–A–S–H) systems deteriorated mainly by decalcification under acid exposure, whereas low-calcium fly ash (N–A–S–H) systems degraded more slowly by dealumination. Seawater activation did not significantly compromise acid resistance relative to distilled-water systems, with the two-activator series performing comparably under both HCl and H₂SO₄. Paired comparisons of the reported blend values showed small, age-dependent differences between the two-activator series: seawater activation modestly delayed strength loss under HCl at intermediate ages, while under H₂SO₄ it carried a small late-age penalty attributable to reaction of activator-derived chloride compounds with the acid; at most ages, the two series were statistically indistinguishable. X-ray diffraction showed essentially identical phase assemblages in the two series: no crystalline products formed under HCl, where an amorphous silica-rich residue accumulates on fly-ash-rich blends, whereas gypsum was the sole crystalline product under H₂SO₄, enhanced in seawater-activated fly-ash-rich blends. The findings clarify the role of marine ions in influencing acid degradation and provide guidance for designing sustainable binder systems for chloride- and sulphate-rich service environments. Overall, seawater is shown to be a viable substitute for potable water in activator preparation, retaining acid resistance comparable to distilled-water systems and supporting the development of more sustainable alkali-activated binders. Full article

In most African countries, supplementary cementitious materials (SCMs), such as silica fume, slag, and fly ash, are scarce, creating a need for alternative low-clinker cement that utilises locally abundant resources. Given the limited availability of SCMs, the development of Limestone Calcined Clay Cement (LC³) has emerged as an attractive solution. LC³ is a blended binder composed of ground limestone, calcined kaolinite clay, and ordinary Portland cement clinker. This research assessed the mechanical and durability properties of LC³ binders formulated using raw materials obtained from selected deposits in Tanzania. Two samples of clay from the Pugu deposit were selected: Pugu hard clay (PH) and Pugu soft clay (PS). Limestone and gypsum were sourced from Dar es Salaam. LC³ mixes containing 58% CEM I/42.5N were produced and used to make concrete with a water/binder ratio of 0.4. Two control mixes were made, a mix with 100% Portland cement CEM I/42.5 N and a mix with 100% Portland pozzolana CEM II/P-B 42.5 N. In addition, four concrete mixes were designed for the study: LC³-PH, LC³-PS, CEM I + PH (CC-PH), and CEM I + PS (CC-PS). The mechanical properties evaluated included compressive strength, splitting tensile strength, and flexural strength, whilst durability performance was assessed through sulfuric acid resistance, water sorptivity, and absorption. The results demonstrated the superiority of LC³ concrete compared to CEM I and CEM II concretes. For instance, the LC³-PS mix achieved a 90-day compressive strength of 63 ± 2.1 MPa, compared with 62 ± 1.8 MPa for CEM I. Similarly, water absorption was 1.35% and 1.1% for CEM I and LC³ concretes, respectively. Under sulfuric acid exposure, LC³ concrete exhibited the lowest mass loss (1.6%) and strength loss (17.9%) compared with 2.4% and 23% for CEM I and 2.1% and 21% for CEM II, respectively. The enhanced performance of LC³ concrete was attributed to its denser and more refined microstructure, which reduced pore connectivity and improved resistance to the ingress of aggressive agents. Full article

Despite the shift toward cleaner energy, coal-fired power plants remain a significant source of global energy, generating excess fly ash that accumulates in large stockpiles—often persisting for decades even after the plants are decommissioned. The study investigated the physicochemical properties and suitability of fly ash recovered from seven ash dams for use in cement-based applications. The recovered ash was beneficiated by drying, breaking agglomerates, and sieving to meet specifications for use as a cementitious material. Subsequently, analyses were conducted for particle size, pH, density, loss on ignition, scanning electron microscopy, oxide composition, X-ray diffraction, thermogravimetry, Fourier transform infrared spectroscopy, and the compressive strength of mortar samples. The results indicate that the samples are Class F fly ashes, containing amorphous aluminosilicates, with a comparable physical, chemical, and mineralogical composition, and that they meet specifications for use in cement-based materials. This remains true despite a slight increase in sulphur-bearing phases in the Kusile ash associated with the plant’s desulfurization technology. Furthermore, the compressive strength results show that, compared with the reference Portland cement mortar, fly-ash-blended mortars exhibit higher strength gain at later ages, indicating good pozzolanic reactivity, though the degree of strength gain depends on each ash’s fineness, amorphous content, and mineralogy. Full article

This study evaluates a wet-activated multicomponent organomineral modifier for sustainable concrete. The modifier was produced by co-grinding Portland cement and rice husk ash (RHA) in the presence of Sika^® ViscoCrete^®-20HE and was subsequently combined with polypropylene fibers. Three modified mixtures were tested after 28 days of curing and compared with a control concrete. The modified concretes achieved compressive strengths of 42.2–45.0 MPa, compared with 36.8 MPa for the control. Among the tested formulations, Mix 2, containing 6 wt.% RHA, 4 wt.% polypropylene fibers, and 1.3 wt.% superplasticizer, showed the most favorable overall performance. Its compressive and flexural strengths reached 45.0 and 5.8 MPa, corresponding to observed differences of 22.3% and 26.1%, respectively, relative to the control formulation. Because the complete mixture compositions and w/c ratios differed, these comparisons do not isolate the contribution of any individual constituent. Fracture toughness increased from 1.15 to 2.16 MPa·m^1/2, water absorption decreased from 6.8% to 5.1%, and freeze–thaw resistance increased from 138 to 242 cycles. Qualitative SEM and XRD observations showed morphological and phase-related differences between selected control and modified specimens; however, these observations did not establish the causes of the measured performance differences. In addition, because no compositionally identical non-activated RHA reference or direct reactivity test was included, the independent effect of wet activation on RHA reactivity could not be established. The investigated integrated modifier therefore shows potential for improving concrete performance while enabling the beneficial use of RHA. Full article

The growing accumulation of coal combustion by-products necessitates the development of sustainable approaches for their utilization in construction materials. This study investigates the production of sintered fly ash aggregate (SFAA) using hydraulic ash waste from the Kyzylorda Combined Heat and Power plant and evaluates its suitability as a coarse aggregate for lightweight cementitious composite. Hydraulic fly ash and clay from the Talsuat deposit were pelletized and sintered at 1100 °C. The physicochemical, mineralogical, and microstructural characteristics of the raw materials and produced aggregate were examined using X-ray fluorescence, X-ray diffraction, scanning electron microscopy with energy-dispersive spectroscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The developed aggregate exhibited a bulk density of 1118 kg m⁻³, water absorption of 5.4%, crushing strength corresponding to grade M200, and frost resistance of at least F35. Mineralogical analysis revealed quartz and mullite as the predominant crystalline phases, while microstructural observations confirmed the formation of a stable porous aluminosilicate matrix. Chemical durability tests in alkaline, chloride, and sulfate media demonstrated high resistance to aggressive environments. Lightweight cementitious composite produced with the aggregate achieved an average density of 1657 kg m⁻³, compressive strength of 3.87 MPa, and water absorption of 16.0%, corresponding to density grade D1600 and strength class B3.5. The results confirm the feasibility of converting hydraulic ash waste into a durable lightweight aggregate suitable for structural-insulating lightweight cementitious composite, contributing to waste valorization, conservation of natural resources, and sustainable construction practices. Full article

In this study, a polymer-modified fast-hardening and early-strength cement-based repair material was proposed, using the polymer cellulose ether (HPMC), polymer dispersible polymer powder (VAE) and silica fume. The optimal mixing ratio of the three polymers was designed by an orthogonal test by combinational evaluation of the fresh performance and mechanical properties, complemented by the observation of the changes in the macroscopic properties by XRD and SEM analysis. The results showed that the content of HPMC has a more significant effect on fluidity, consistency and water retention than other factors, and the content of silica fume has a more significant effect on setting time. The content of HPMC is the most important factor affecting the compressive strength and flexural strength. The content of HPMC and VAE has a more significant effect on the interfacial bonding performance, the 1-day interfacial bond strength was significantly higher than that without polymer. According to the SEM results, it was observed that, the porous structure of Ca(OH)₂ induced by VAE, and the polymer film formed by HPMC covering the hydration product, the two polymers work together to significantly improve the interfacial bond strength of cement mortar. The optimal mixing ratio of the two interface bonding methods is the same, so the optimal mixing ratio of three factors is obtained: 0.2% of cellulose ether, 0.6% of redispersible polymer powder, and 10% of silica fume strong and fluid repair material. Full article

This study evaluates the performance of a rehabilitation mortar in controlling chloride ion migration in artificially contaminated ceramic masonry under controlled laboratory conditions. Coatings with thicknesses of 3 cm, 5 cm, and 7 cm were applied to ceramic brick substrates saturated with saline solution and exposed to accelerated contamination. Chloride concentration profiles were determined by potentiometric titration after 120 days of curing. The results showed that the rehabilitation mortar effectively retained soluble salts within its porous matrix, limiting their migration toward the surface. The 3 cm coating provided satisfactory salt retention and reduced the potential for surface efflorescence. Among the evaluated thicknesses, the 5 cm coating exhibited the most favorable chloride distribution, characterized by a pronounced concentration peak at the substrate–mortar interface followed by a sharp decrease toward the external surface, indicating the formation of an effective chloride retention zone. In contrast, the 7 cm coating showed a more homogeneous ion distribution but a less defined retention profile. The results demonstrate the potential of the rehabilitation mortar to act as a protective barrier under controlled laboratory conditions using artificially contaminated ceramic substrates. These findings provide experimental evidence that may support future applications in salt-contaminated historic masonry, although further validation under real field conditions is still required. 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

Graphene oxide (GO) has been widely reported to enhance the mechanical performance of cementitious composites. However, the fundamental hydration mechanisms underlying these improvements, such as GO’s role as a nucleation site, remain poorly explored and quantified. This study presents a comprehensive, non-destructive investigation into the time-dependent hydration behaviour of GO-induced cement pastes using time-domain ¹H Nuclear Magnetic Resonance (NMR) spectroscopy, supported by thermogravimetric analysis (TGA), humidity-controlled water-retention tests, and compressive strength tests. Cementitious composites containing 0.035%, 0.065%, and 0.08% GO by weight of cement (bwoc) were monitored from 4 h to 28 days to track the evolution of discrete water phases, including capillary, inter-hydrate, gel pore, and interlayer water. NMR results reveal that GO initially facilitates water redistribution by retaining free water within its layered structure, followed by a delayed but sustained release that promotes continued hydration and a progressive shift toward less mobile pore–water environments at later curing ages. TGA confirms enhanced formation of hydration products in GO-induced cementitious systems, with an optimal dosage of 0.035% bwoc achieving the most sustained hydration and highest compressive strength. Higher GO dosages accelerate early hydration but limit later-stage hydration due to diffusion barriers formed by hydration products. This study provides time-dependent scientific evidence of GO’s dual role as a hydration nucleation agent and water-release regulator, establishing a mechanistic basis for dosage optimization in nano-engineered cementitious composites. Full article

The structural performance of reinforced concrete (RC) deep beams in both ultimate and serviceability limit states (ULSs/SLSs) is influenced by beam size effects and the adopted reinforcement ratios. In this study, the effects of cotton waste fibres (CWFs) and beam depth were studied using a four-point load test on five sets of 400 mm and 500 mm CWF high-strength RC deep beams with a 0.3% web reinforcement ratio. Control unnotched and notched, and notched specimens with 0–0.75% CWF content in each specimen set, were studied. The failure modes, stirrup and strut-and-tie zones’ strains, shear capacity, and load-deflection were analyzed. It was observed that the beam failure evolved from shear-compression in unnotched specimens to the web-splitting failure phenomenon in notched ones, coupled by 27.44% and 0.17% decline in ultimate shear capacity ($V_u$) in notched 400 mm and 500 mm beam sets, respectively. The notched RC deep beam specimens, mimicking the SLS shear performance parameters, showed a 34.28% and 14.71% $V_u$ increase in 400 mm and 500 mm depth beams, respectively. The crack opening load increased from 13.87 kN to 44.63 k and from 11.88 kN to 35.19 kN in these beam sets, respectively. In a similar analysis, 84.76% and 38.39% stiffness increase, and 49.15% and 39.95% shear ductility index increase in the outer-most stirrup, were observed in the respective specimen sets. The contribution factor of the shear reinforcement to $V_u$ improved from 0.31 to 0.94, and from 0.87 to 0.97 in 400 mm and 500 mm, with 0% and 0.75% CWF, respectively. These experimental results confirm the contribution of beam size effect and fibres to the shear performance properties of RC deep beams. The feasibility of using CWF in structural concrete is confirmed by its improvement of the SLS properties of the studied RC deep beam specimens with light shear reinforcement. Full article

This study developed a conditioning framework for the sustainable use of waste-engine-oil-modified binders (WEOMBs) in 100% reclaimed asphalt pavement (RAP) mixtures. Binder with a penetration grade of 60–70 was modified by 5%, 8%, and 10% waste engine oil (WEO) by binder weight. The WEOMBs were subjected to physical, chemical, and compositional analyses. For 10% WEOMB, the results showed a reduction of the binder softening point by 18% and an increase in binder penetration of almost 8%, enhancing softening and the workability of the binder. Binder chemical and compositional analyses verified that WEO altered the binder’s colloidal structure by augmenting aliphatic fractions and molecular mobility, while diminishing resin content and promoting saturates plus aromatics content. At 160 °C for 45 min, the RAPs were conditioned with 1% WEOMB (containing different WEO percentages) by the total weight of the RAP mixture. Among all the conditioned mixtures, the 100% RAP modified with 1% WEOMB, containing 8% WEO, showed the best performance. Dynamic modulus and phase angle analyses demonstrated that RAP conditioning reduced excessive stiffness and produced a balanced viscoelastic response, enhancing the rutting resistance. The proposed conditioning framework demonstrated the feasibility of producing fully recycled mixtures with balanced mechanical performance and adequate cracking resistance. Full article

Since 2024, most electricity production on Réunion Island has been achieved through combustion of biomass, using either imported wood pellets or locally produced bagasse. Their combustion generates two types of ash, depending on the biomass source: Wood Biomass Fly Ash (WBFA) and SugarCane Bagasse Ash (SCBA). Their chemical compositions differ significantly, leading to different potential applications. The composition of SCBA is similar to that of Coal Fly Ash (CFA), with low variability between batches. Therefore, SCBA could be used as an alternative to CFA, as a Supplementary Cementitious Material (SCM) or in composite cements. SCBA also meets most of the requirements of the NF EN 450-1 standard. However, grinding of SCBA appears necessary to achieve mechanical performance required by the standard. In contrast, WBFA exhibits variable chemical composition, mainly due to differences in pellet origin prior to combustion. Nevertheless, WBFA contains significant levels of chloride ions and sulfate, which may act as activators for materials such as GGBS or metakaolin (MK). Although the high unburned carbon content of WBFA increases water demand, their incorporation into GGBS-based binders (SSC or CEM III) or metakaolin-based systems shows promising potential, particularly for improving early strength. Full article

The growing demand for sustainable construction materials has stimulated interest in alternative binders derived from waste resources. This study investigates the use of calcined crab shell (CCS), a calcium-rich marine biowaste, as a partial replacement for Portland limestone cement. Cement pastes containing 0%, 5%, 10%, and 15% CCS were prepared and evaluated through compressive strength, water absorption, open porosity, bulk density, SEM, XRD, FTIR, and TGA analyses. The results showed that incorporating 10% CCS produced the most favorable performance, increasing compressive strength from 17.6 MPa to 33.6 MPa after 28 days of curing. This improvement was accompanied by reduced porosity, increased bulk density, and the development of a denser and more homogeneous microstructure. Physicochemical analyses suggest that CCS acts both as a filler and as a source of reactive calcium species. The CaO generated during calcination may participate in hydration processes and influence the formation of hydration products, contributing to matrix densification. In contrast, the incorporation of 15% CCS resulted in increased porosity, a less homogeneous microstructure, and lower mechanical performance. These findings indicate that replacing Portland limestone cement with up to 10% CCS can improve the properties of cement pastes while promoting the valorization of marine shell waste and reducing cement consumption, thereby supporting the development of more sustainable construction materials. Full article

The growing use of reclaimed asphalt pavement (RAP) in hot mix asphalt (HMA) is an important practice to achieve more sustainable pavements, as it reduces the consumption and environmental impact of virgin materials. However, aging induces binder stiffening that requires effective rejuvenation to restore overall performance. This study provides a comprehensive comparative analysis of ten chemically different waste oils—waste engine oil (WEO), waste cooking oil (WCO), yellow grease (YG), waste hydraulic oil (WHO) waste electric transformer oil (WETO), slop oil (SO), sludge-derived bio-oil (SDBO), tire pyrolysis oil (TPO), plastic pyrolysis oil (PPO), and algal residue oil (ARO)—as recycled HMA mixture rejuvenators, linking oil composition to binder regeneration and mixture performance. Binder properties were determined by rotational viscosity (RV), dynamic shear rheometer (DSR) and bending beam rheometer (BBR), whereas mixture performance was assessed in terms of Superpave mechanical properties, Hamburg wheel-tracking test (HWTT) for rutting resistance and mixture BBR for low-temperature cracking resistance. Performance grade (PG) evaluations showed that WETO and WEO restored the 50% and 75% RAP binders, respectively, to a grade close to PG 64-16 at the lowest dosages. The Superpave volumetric properties of all restored mixtures were similar to those of the control mixture, denoting corrected mixture balance and compaction level. HWTT results indicated that WETO-recycled mixtures revealed the lowest rut depth at 50% RAP, while WEO-recycled mixtures exhibited the lowest rut depth at 75% RAP after 20000 passes. Additional evidence supporting these results can be found in BBR mixture data, which demonstrated that WETO at 50% RAP and WEO/WETO at 75% RAP showed the most reduction in creep stiffness and improvement in creep rate. The correlation, regression, and PI analyses were in good agreement with the experimental results, where WETO and WEO exhibited the best overall performance at 50% and 75% RAP, respectively. In summary, these results indicate that the performance of waste oil rejuvenator in recycled HMA mixtures is highly dependent on RAP content and point to WETO and WEO as feasible, environmentally friendly options for high-RAP recycled HMA. Full article

Zinc processing generates large volumes of tailings enriched with potentially toxic elements such as zinc, lead, arsenic, and antimony, creating environmental challenges. Conventional disposal in tailings dams is associated with land occupation, contamination risks, and geotechnical concerns, reinforcing the need for more sustainable management strategies. This study presents a bibliometric and semi-systematic review of alkali-activated binders for the stabilization and solidification of zinc mine tailings, based on nine studies published between 2019 and 2026. The results indicate that this is a recent and expanding research field, with a marked concentration of studies in China. Current research mainly focuses on the links between microstructure, heavy metal immobilization, and mechanical performance. Alkali-activated systems, commonly based on blast furnace slag, fly ash, and coal gangue, can produce dense matrices with compressive strengths of up to 100.77 MPa and high immobilization efficiency. Their performance is largely governed by the type of reaction products formed, particularly calcium silicate hydrate, calcium aluminosilicate hydrate, and sodium aluminosilicate hydrate gels, which control microstructural development and stabilization mechanisms such as encapsulation, structural incorporation, and secondary phase formation. Overall, the reviewed studies suggest that alkali-activated binders have potential as alternative binders to Portland cement for the management and valorization of zinc mine tailings. Full article

Basalt-fiber-reinforced recycled aggregate concrete (BFRAC) produced with 100% recycled coarse aggregate is still constrained by the inferior quality of recycled aggregate and the difficulty of optimizing fiber reinforcement parameters. This study investigated the effects of basalt fiber length configuration and dosage on the mechanical performance and pore structure of recycled aggregate concrete incorporating recycled coarse aggregate subjected to two-step pretreatment with nano-silica and cement slurry. Four fiber length configurations, namely 6, 12, and 24 mm and a mixed-length system, were evaluated at volume fractions of 0.1, 0.2, and 0.3%. The reinforcing effect was assessed through compressive strength, splitting tensile strength, scanning electron microscopy, mercury intrusion porosimetry, and statistical analysis. The pretreatment improved recycled aggregate quality, reducing water absorption from 4.97% to 3.11% and crushing index from 20.5% to 13.4%. Basalt fiber incorporation generally enhanced mechanical performance, although the response depended on fiber length and dosage. At 28 days, BF24V1 achieved the highest compressive strength, whereas BFmixV1 exhibited the best overall performance by combining high compressive strength with the highest splitting tensile strength. Relative to the average performance of the corresponding single-length mixtures at the same dosage, the mixed-length system showed a positive synergistic effect. Microstructural observations indicated that this behavior was associated with more effective crack bridging and refinement of the pore-size distribution. The results demonstrate that a low-dosage mixed-length basalt fiber system provides an effective route for upgrading pretreated waste-derived aggregate into higher-performance recycled aggregate concrete. Full article

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