Search Results (614)

This research investigates the formation and behavior of sustainable crumb rubber-modified gypsum–cement–pozzolan (GCP) composites, with a view to their use in a broad concept for construction. GCP binders are gaining attention as a low-carbon replacement for Portland cement, and the addition of recycled rubber helps the achievement of circular economy goals and potentially increases durability. The present research evaluates the impact of crumb rubber (CR) on the mechanical strength, water absorption, dimensional stability, and freeze–thaw resistance of 3D-printed GCP-rubber composites. Composite blends of variable proportions of crumb rubber were prepared at constant binder ratios. Mechanical properties were defined by prism specimens (40 × 40 × 160 mm) by the flexural and compressive strengths, and deformation was determined by micrometers to measure longitudinal strain as a function of curing. Water absorption was determined prior to freeze–thaw cycling to define pore saturation. Durability was investigated using two approaches: (1) controlled freeze–thaw experiments on cube specimens, with XF1 grade performance achieved, and (2) ultrasonic pulse velocity (UPV) testing of specimens 3D-printed for assessing internal structural change after long-term frost exposure. Results showed that compressive strength decreased moderately (10–20%) with increasing rubber content from 17% up to 50%, while flexural strength improved up to 15%, showing the elastomeric action of CR. Water absorption was reduced by 5–8% in the rubber-modified blends due to the hydrophobic character of rubber. Deformation tests also confirmed minimum length variation (<0.02%) during curing. Freeze–thaw durability was enormously improved, and test specimens retained more than 95% of initial strength. UPV measurements detected only a relatively modest velocity drop (~50 m/s) after 36 days cycling with subsequent stabilization up to 200 days, demonstrating long-term internal structure with minimal progressive damage. In summary, the findings demonstrate that GCP composites with crumb rubber incorporated are printable, dimensionally stable, and capable of freeze–thaw degradation resistance. Despite a moderate loss of compressive strength, the balance of introduced durability and sustainability suggests their competence as viable materials for additive manufacturing in construction. Full article

This study develops a ternary Fe-based geopolymer system composed of metakaolin (MK), red mud (RM), and fly ash (FA) for the preparation of sustainable water-retaining subgrade materials for sponge-city roadbed applications. Unlike conventional formulations primarily designed for structural strength or rapid permeability, the proposed MK–FA–RM system was designed to improve water-storage capacity while maintaining adequate mechanical support and environmental compatibility. In this ternary system, MK provides highly reactive aluminosilicate species for geopolymer network formation, RM introduces Fe-bearing phases and enhances industrial solid-waste utilization, and FA contributes to particle packing, workability, and resource efficiency. A constrained ternary mixture design implemented using Design-Expert software was adopted to optimize precursor proportions. Within the investigated compositional range, the fitted first-order mixture model showed acceptable statistical adequacy for preliminary composition screening (R² = 0.86). The optimal blend (60% MK, 30% RM, and 10% FA) achieved a 7-day compressive strength of 8.37 MPa and a water retention rate of 35.3% under ambient curing conditions, satisfying the strength requirement considered for the target subgrade/base-layer application. Microstructural and phase analyses suggest that the synergistic interaction of the three precursors promoted Fe-modified aluminosilicate gel formation together with conventional geopolymer gel products, while improving matrix continuity and preserving interconnected pore space for water storage. This multiscale structural effect helps explain how the material achieved a balance between water retention capacity and mechanical support. Under the tested conditions, the material maintained acceptable residual strength after short-term exposure to water, acid, and sulfate-containing solutions. Life-cycle assessment indicated a 70% reduction in CO₂ emissions compared with ordinary Portland cement, while pilot-scale cost analysis showed a 39% lower production cost than MetaMax-based geopolymer materials. Pilot-scale application further demonstrated the constructability and water-regulation potential of the material in practical environments. Overall, the proposed ternary Fe-based geopolymer demonstrates that Fe-rich industrial wastes can be engineered into low-carbon and economically viable water-retaining subgrade materials that balance hydraulic regulation, structural adequacy, and sustainability. Nevertheless, long-term durability, cyclic loading performance, and direct nanoscale characterization of Fe-bearing gel evolution still require further investigation. Full article

Current industry standards for evaluating concrete durability in wastewater environments, such as ASTM C267, rely almost exclusively on mass loss as the primary performance indicator. This study demonstrates that mass change alone can be an ambiguous metric that does not fully characterize the structural degradation of advanced cementitious binders. Through a comprehensive physical, chemical, and mechanical evaluation of 27 binary and ternary mixtures (totalling 486 specimens), we identify four limitations of mass-based standards: (1) The Slag Anomaly, where excellent surface mass preservation masks a significant loss of internal structural capacity, indicating potential internal structural softening. (2) The Sewage Anomaly, where specimens in active biogenic environments exhibit mass gain (up to +1.21%) despite continuous chemical attack. (3) Non-Linear Scaling, where 5% “accelerated” acid tests fundamentally alter degradation kinetics compared to realistic 1% environments. (4) The Maturation Conflict, where extended curing (56 days) significantly improves the physical resistance of slow-reacting pozzolans (cyment) while increasing the mass loss of high-performance ternary blends (MK/SF), likely linked to the exhaustion of their chemical buffering capacity. Current standards relying solely on mass loss may not capture internal degradation in slag-based cements that remain geometrically intact. We propose residual flexural strength as a necessary complementary metric. Full article

The stability of upstream tailings remains a critical geotechnical challenge due to the inherently weak mechanical properties of fine-grained mine tailings. This study investigated a tailing improvement method using (i) emulsified polymer and (ii) combinations of recycled gypsum and cement kiln dust (CKD). A comprehensive experimental program—including unconfined compressive strength (UCS) analysis, direct shear tests (DSTs), and oedometer consolidation tests—was conducted to assess the performance of various treatment mixtures. The results showed that blends of CKD and gypsum, particularly at a 1:2 ratio and a 10% dosage, significantly improved shear strength, reduced compressibility, and lowered hydraulic conductivity by over an order of magnitude. The inclusion of plaster (commercial gypsum) further enhanced the UCS by more than 100% compared to recycled gypsum and increased the cohesion (c’) values from 0 to 32.8–47.2 kPa. The compression index (c_c) decreased from 0.15 to 0.05, and the maximum volumetric strain (ε_v) at an applied effective stress of 800 kPa decreased from 17% to 5%. Emulsified polymer treatments also enhanced the mechanical and hydraulic properties of the clayey tailings; however, the overall improvements were lower than those achieved with CKD–gypsum blends, suggesting that further optimization of the polymer concentration or its combination with mineral additives may yield better results. These findings offer a foundation for further research into the use of polymers in geoenvironmental applications, particularly for erosion control, contaminant encapsulation, and hydraulic barrier development. Overall, this study highlights the potential of using industrial by-products, such as CKD and gypsum, as sustainable, cost-effective materials to improve tailing performance, while identifying promising directions for polymer-based solutions in geotechnical engineering. Full article

High water-content silty soft soils are widely distributed across coastal regions. Their low strength and high compressibility render them unsuitable for direct use as foundation or subgrade materials. While ordinary Portland cement is the most prevalent chemical stabilizer for ground improvement, its manufacturing process generates substantial CO₂ emissions, significantly exacerbating global climate change. While limestone calcined clay cement (LC³) has emerged as a promising low-carbon alternative in concrete engineering, its multicomponent hydration mechanisms and engineering applicability for geotechnical soft soil stabilization remain a critical knowledge gap. To address this, this study investigates the application of LC³ in ground improvement by systematically evaluating and comparing three novel LC³ blends formulated with distinct types of calcined clay. The mechanical properties of LC³-stabilized soft soil were investigated through unconfined compressive strength and direct shear tests. Furthermore, the underlying stabilization mechanisms and microstructural evolution were revealed using X-ray diffraction and supplementary microanalytical techniques. The results demonstrated that LC³ significantly enhanced the mechanical properties of soft soils by generating abundant C-S-H and C-A-S-H gels, which bound soil particles into a stable, interlocking network. Among the evaluate variants, the calcined kaolin-based cement (LC³-K) exhibited the highest pozzolanic activity, providing to be the optimal stabilizer. However, this stabilization effect was dosage dependent; while an appropriate LC³ application markedly improved soil strength, excessive dosage or elevated clinker proportions induced a highly alkaline environment. This led to charge over-neutralization and deflocculation, ultimately compromising the structural integrity and mechanical performance of the solidified soil. The findings of this study provide a solid theoretical foundation for the application of eco-friendly LC³ in soft soil stabilization, promoting the broader adoption of sustainable, low carbon geomaterials in geotechnical engineering. Full article

Reducing cement consumption in mortar systems is essential for lowering the environmental impact of cement-based materials. Conventional mix design approaches rely mainly on particle size distribution and fineness modulus, which do not fully capture the effects of aggregate packing, morphology, and petrographic composition on paste demand and mechanical performance. Fourteen fine aggregates of distinct geological origins were experimentally characterized in terms of physical and petrographic properties. A dataset of 211 mortar mixtures, yielding 633 transverse-strength observations, was used to train a Random Forest Regressor (RFR) model for strength prediction. The model achieved $R^2=0.762$ (RMSE = 0.223 kN; MAE = 0.165 kN), demonstrating its reliability as a surrogate screening tool. This study presents a hybrid framework that integrates particle packing theory with machine learning to optimize fine aggregate blends. By introducing a Paste Demand Index (PDI)—combining normalized uncompacted void content, surface texture, and shape—the framework enables the identification of mixtures that minimize paste demand while maintaining mechanical performance under strength constraints. Results confirm that the proposed PDI and strength-based filtering are robust, offering a physically grounded decision-support methodology for narrowing the design space. Ultimately, this approach provides an efficient strategy for resource optimization, effectively bridging the gap between computational screening and laboratory validation in cement-reduction initiatives driven by the cement-based tile manufacturing industry. Full article

Achieving low hydration heat without sacrificing strength is essential for early-age temperature-crack control in concrete. This study designed a low-heat Portland cement (LHPC)–fly ash (FA)–ground-granulated blast-furnace slag (GGBS)–silica fume (SF) binder system with LHPC fixed at 80 wt.% and total supplementary cementitious materials (SCMs) fixed at 20 wt.%. Compressive strength at 3, 7, and 28 d, 7 d isothermal calorimetry combined with Krstulović–Dabić (K–D) modeling, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were used to identify a low-heat/high-strength pathway. The mixture containing 20 wt.% FA (F20) reduced the 7 d cumulative heat to 194.060 J·g⁻¹ but lowered the 28 d compressive strength to 44.2 MPa. Replacing FA with GGBS under the same replacement level restored the strength baseline, and the mixture containing 20 wt.% GGBS (G20) reached 56.7 MPa. Introducing SF created an optimum compositional window, and the mixture containing 10 wt.% FA, 3 wt.% GGBS, and 7 wt.% SF (F10G3S7) achieved the highest 28 d strength of 58.2 MPa. Notably, the mixture containing 10 wt.% FA, 9 wt.% GGBS, and 1 wt.% SF (F10G9S1) combined relatively low 7 d heat (203.545 J·g⁻¹) with high 28 d strength (54.2 MPa). K–D fitting showed that FA lowered the heat potential (Qmax = 217.98 J·g⁻¹) relative to LHPC (236.19 J·g⁻¹), whereas GGBS/SF blends increased Qmax to 268.77–271.55 J·g⁻¹, indicating composition-dependent hydration efficiency. TGA revealed higher bound water per unit LHPC at 28 d (21.46–22.97%) than in LHPC alone (17.17%), and bound water correlated more strongly with compressive strength (R² = 0.75–0.78) than calcium hydroxide (CH) content (R² = 0.66–0.67). SEM confirmed a more continuous gel-rich matrix in F10G9S1, suggesting that the low-heat/high-strength route is governed by efficient heat-to-hydrate conversion and microstructural densification rather than heat output alone. These findings provide both mechanistic insight and practical guidance for proportioning low-heat, high-strength binders for concrete applications requiring early-age temperature-crack control. Full article

An investigation was conducted to explore the freeze–thaw resistance of 60–90 MPa high-strength concrete blended with multiple industrial byproducts (limestone powder, fly ash, etc.) and mixed sand (machine-made/tailings sand), aiming to clarify freeze–thaw degradation mechanisms and build reliable damage prediction models. Three water-binder (w/b) ratios (0.30, 0.25, 0.20) and 15 mix proportions were designed, with 30–45% cement replaced by mineral admixtures and 90–100% natural sand by mixed sand. Results show lower w/b ratios improve resistance: the 0.20 ratio yields merely 0.06% mass loss and 96% relative dynamic elastic modulus retention after 400 cycles. Optimized silica fume and limestone powder refine pore structures; fly ash-slag synergy boosts durability via secondary hydration under specific dosage ratios. A 7:3 machine-made/tailings sand mix shows better frost resistance due to improved particle packing and interfacial transition zones. Three damage models were established, with Model III demonstrating high accuracy. This work’s novelty lies in multi-byproduct synergy and multi-factor models, supporting green concrete use in cold regions. Full article

Engineered cementitious composite (ECC) is an advanced material known for its superior flexibility, high durability, and crack resistance, making it ideal for a variety of structural applications. However, it uses cement at a rate of 2–3 times more than conventional concrete which raises environmental concerns. This study focused on the production of eco-friendly ECC by incorporating various waste materials as partial cement and sand substitutes. Cement kiln dust (CKD), ceramic powder waste (CPW), and eggshell waste (ESW) were used as partial substitutes for cement in doses of 10% and 20%. Crumb rubber (CR) was used as a partial substitute for sand in doses of 25, 50, 75, and 100%. Chemical treatments using sodium hydroxide, sodium silicate, and a mix of both of them were carried out for the CR in the production of the proposed ECC. Physical treatment using the same cement substitute materials (CKD, CP and ESP) was also carried out for the CR. The effect of fiber type—such as basalt fibers (BF), polypropylene fibers (PPF), and steel fibers (S_tF)—on the performance of ECC was also investigated. Slump, compressive strength, uniaxial tensile strength, flexural strength, and sorptivity were the measured properties for the proposed ECC. Microstructure analyses were also conducted on some selected ECC mixtures. Among the tested mixtures, the results showed that replacing 10% of the cement with CKD improved the compressive strength by up to 22.6% and the tensile strength by up to 18.3%. Using 50% untreated CR reduced compressive and tensile strength by 32.8% and 28.1%, respectively, compared to the control ECC. The physical treatment of CR using CKD improved the compressive strength by up to 12.7% and the tensile strength by up to 3.2% compared to untreated CR. The microstructure analyses revealed an improvement in fiber-matrix bonding and a reduction in crack width in the mixtures, especially in the BF and PPF blends. Full article

To enhance the engineering performance of fine-grained composite soils with unbalanced particle gradation, high plasticity, and poor water stability, a synergistic stabilization strategy combining particle structure regulation and microbially induced calcium carbonate precipitation (MICP) was proposed. The particle size distribution and fundamental engineering properties of a titanium gypsum–clay (TSC) composite soil were first optimized through systematic single-factor blending tests. The results indicate that a TS:C ratio of 60:40 significantly improved gradation characteristics, reduced plasticity, and enhanced both compaction behavior and load-bearing capacity. Based on the optimized gradation framework, MICP treatment was subsequently introduced to further enhance water stability. The effects of key parameters, particularly the type of calcium source, on the evolution of water stability were systematically investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to elucidate the underlying reinforcement mechanisms. The results demonstrate that the water stability coefficient increased markedly from 0.35 to 0.83 following MICP treatment, while strength degradation under water immersion was effectively mitigated. Microscopic observations reveal that microbially precipitated calcite fills pore spaces and forms a continuous cementation network via particle bridging and interfacial bonding, leading to an approximately 32% reduction in porosity. Overall, the proposed synergistic strategy offers an effective and sustainable approach for improving the water stability and structural integrity of complex fine-grained composite soils. Full article

This study used calcium hydroxide (CH) to simulate the alkaline environment of cement and to activate lithium slag (LS), aiming to reveal the mechanism of LS in cement. The early-age hydration of LS blended with 10 wt.% CH was monitored via isothermal calorimetry (ICC) at ambient temperature, followed by a comparative analysis of phase assemblage, microstructure, and macroscopic properties under standard and steam curing conditions. The results show that LS exhibits superior early reactivity within the first 9 h, which is attributed to abundant ettringite formation. Two distinct exothermic peaks were identified during LS-CH hydration, corresponding to (i) ettringite formation accompanied by LS dissolution and C–S–H precipitation, and (ii) CaCO₃ crystallization and renewed ettringite formation. The hydrated paste consists of abundant AFt, CaCO₃ polymorphs, unreacted LS particles, and a small amount of C–S–H gel with a low Ca/Si ratio and incorporating Al and S. This unique phase assemblage results in a coarser pore structure and lower specific surface area compared with conventional cement paste. Nevertheless, the system achieves a relatively high 28-day compressive strength, highlighting the promise of LS-CH blends as sustainable cementitious materials. Full article

Since 2007, the porosity–to–cement relationship has been widely used as a unified parameter to predict mechanical strength, durability, expansion, and stiffness of stabilized soils. In this formulation, the volumetric binder content is adjusted by an internal exponent x, typically ranging between 0 and 1, to balance the relative contributions of porosity and cementation. Traditionally, the parameters of this relationship have been obtained using manual regression procedures. This study proposes an automated calibration methodology for the porosity–binder index, where the parameters A, B, and x are determined through an iterative optimization framework based on minimization of the sum of absolute errors (SAE) combined with a Monte Carlo search algorithm. The methodology is applied to a cement-stabilized clay blended with ground glass (GG), recycled gypsum (GY), and limestone residues (CLW). The predictive capability of the calibrated model is evaluated using unconfined compressive strength (q_u) and initial shear stiffness (Go) datasets. Two calibration strategies are considered: Calibration Process No. 1, based on CLW mixtures and q_u values only, and Calibration Process No. 2, incorporating all mixtures (CLW, GG, and GY) and both q_u and Go responses. The results indicate that Calibration Process No. 2 provides a more robust and physically consistent parameter set, yielding coefficients of determination of 0.9318 and 0.9412 for q_u and Go, respectively. The proposed algorithm-driven calibration framework improves predictive capability and provides a systematic approach for determining the parameters of the porosity–binder relationship. Full article

Cement production accounts for approximately 8% of global CO₂ emissions, and while calcined clays have attracted growing attention as supplementary cementitious materials, the literature remains fragmented across clay types and performance metrics, with no unified comparative framework examining how mineralogical composition and calcination conditions jointly govern pozzolanic reactivity and downstream performance outcomes. This study addresses that gap through a PRISMA-guided systematic review of 32 peer-reviewed studies, validated by structured expert interviews, and a comparative assessment of five calcined clay categories: metakaolin (MK), limestone-calcined clay blends (LC³), illite-rich clays, montmorillonite (MM)- based clays, and ceramic waste (CW)- derived clays. Findings establish clear performance hierarchies with direct implications for the construction sector. MK at 10–15% cement replacement delivers compressive strength gains of 8–36%, chloride permeability reductions of 61–87%, and sulphate expansion reductions of up to 89%, confirming its suitability for high-performance, chemically aggressive-environment structural concrete. LC³ systems enable 30–50% clinker substitution, yielding an estimated 30–40% embodied CO₂ reduction alongside 6–10% strength gains and 64–90% reductions in chloride migration, representing the most significant decarbonisation opportunity reviewed. Illite-rich clays reduce compressive strength by 6–25%, limiting application to non-structural uses despite moderate durability gains. MM-based clays exhibit highly variable performance, ranging from a 60% strength loss to an 8% gain, with workability penalties of up to a 90% slump reduction, constraining adoption. CW-derived clays achieve 50–69% reductions in chloride diffusion while valorising industrial waste, though strength reductions of 11–20% limit structural applications. Across all clay types, superplasticiser demand increases by 1.5–3.6 times, posing a universal cost and logistics challenge for practitioners in mix design. Full article

This study investigates the development of sustainable dry-mix shotcrete incorporating fly ash and silica fume as partial cement replacements in order to reduce the environmental impact of cement production. A total of 24 mixtures were systematically evaluated, with 10–30% supplementary cementitious material and 0.9–1.8 kg/m³ polypropylene fiber dosages. This research establishes a quantitative framework for optimizing mechanical performance, durability, and Global Warming Potential. Experimental results reveal that silica fume replacement increases 28-day compressive strength by up to 31.13%, while an optimal polypropylene fiber dosage of 0.9 kg/m³ provides a 15.87% strength enhancement through a matrix-bridging effect. Conversely, excessive fiber content (1.8 kg/m³) increases porosity, leading to a 14.94% reduction in strength. Durability analysis demonstrates that silica fume and fly ash significantly refine the microstructure, reducing sorptivity and limiting freeze–thaw strength loss to a range of 18.13% to 41.03%. Crucially, the 30% by volume of the cement replaced with silica fume mixture was identified as the optimum design, achieving the lowest Global Warming Potential per unit strength at 8.82 kg CO₂-eq/m³/MPa, compared to 18.75 for the high-fiber mixture. These findings provide new, specific evidence that these supplementary cementitious material blends can successfully produce dry-mix shotcrete with significantly lower carbon emissions. Full article

The growing demand for sustainable construction has highlighted the need to effectively utilize solid waste materials in concrete production, yet achieving satisfactory workability, strength, and durability simultaneously remains challenging. A multi-parameter mix-design methodology is proposed for solid-waste-based self-compacting concrete (SCC). This method couples minimum water demand, control of paste film thickness, and multi-performance balancing. The ternary solid-waste powder system (silica fume, fly ash, and supersulfated solid-waste-based cement) was first optimized through minimizing water demand to achieve maximum packing density. The resulting composition was then blended with varying dosages of ordinary Portland cement (OPC) to form the final cementitious binder. Aggregate gradation was proportioned to minimize voids, and paste volume was determined using an equivalent-paste-film-thickness model. Under comparable mixture conditions, SCC with OPC contents of 70–40 wt.% and paste film thicknesses of 2.0–2.6 mm was evaluated for fresh performance, compressive strength, freeze–thaw resistance, and material cost. Mixtures with a paste film thickness of 2.4 or 2.6 mm satisfied the self-compactability criterion—the mix with 50 wt.% OPC and a paste film thickness of 2.4 mm showed the best overall performance balance, achieving higher 28 d strength than higher-OPC mixtures while improving freeze–thaw resistance and reducing cost. Results from TGA, XRD, ATR–FTIR, and SEM–EDS analyses indicated enhanced calcium hydroxide (CH) consumption, increased formation of C-(A)-S-H and ettringite, and a denser interfacial transition zone (ITZ), supporting the proposed multi-objective design approach. While the framework was validated for a specific ternary binder system, it provides a reproducible proportioning strategy applicable to a broader range of solid-waste-based concrete systems, with potential for extension to other waste streams and exposure conditions, thus supporting the development of more resource-efficient and environmentally sustainable concrete. Full article