Search Results (240)

To address the rapid flash setting of NaOH-activated slag and promote high-volume utilization of coal-based solid wastes, this study investigated the synergy of fly ash (FA), coal gangue (CG), and gasification slag (GS) in partially replacing granulated blast furnace slag (GBFS) for NaOH activated binders, aiming to mitigate flash setting while preserving mechanical performance. Binary and ternary pastes with up to 90 wt% substitution were evaluated for setting time, fluidity, and compressive strength, supported by quantitative XRD and SEM. The G8F1G1 achieved the optimal balance, extending initial and final setting times from 28 and 32 min to 35 and 43 min, yielding a fluidity of 218 mm, and maintaining a 28-day strength of 48.5 MPa, equivalent to neat GBFS. The FA-GS synergy suppressed crystalline by damping the Ca²⁺ supersaturation peak through FA derived oligomers while providing nucleation sites via fine carbonaceous particles in GS, thereby retaining the amorphous C-A-S-H gel at approximately 77 wt%. This preserved the load-bearing gel network but eliminated early percolating crystalline frameworks, extending workability without strength loss. In contrast, CG acted as an inert diluent, introducing weak interfaces and porosity that severely degraded strength. A critical amorphous threshold near 64 wt% (G6F2G2, amorphous gel) governed the transition to a granular bed. The FA-GS system offers an effective route for high-volume valorization of coal-based solid wastes in sustainable construction materials. Full article

High-volume fly ash binder and aeolian sand have been widely used in the production of low-carbon ultra-high performance concrete (UHPC) owing to their environmental and economic benefits. However, such low-carbon UHPC still faces the volume stability issues, including autogenous shrinkage, drying shrinkage and early-age cracking. In this study, a superabsorbent polymer (SAP) was incorporated into low-carbon UHPC containing high-volume fly ash and aeolian sand to improve its volume stability through internal curing. The effects of SAP particle size and dosage on the mechanical properties and volume stability of low-carbon UHPC were investigated. Results showed that the addition of 0.3% SAP with a particle size of 180–600 μm significantly reduced shrinkage and early-age cracking while maintaining the compressive strength. Furthermore, the microstructure of low-carbon UHPC was characterized using advanced techniques to shed light on the underlying mechanisms. Full article

Circulating fluidized bed (CFB) fly ash exhibits immense potential as a supplementary cementitious material, yet its application is limited by volumetric instability related to delayed ettringite formation. This study investigates the effect of grinding and ultrafine grinding on hydration behavior, microstructure, and long-term volumetric stability of CFB fly ash–cement composites using isothermal calorimetry, XRD, SEM-EDS, TG-DSC, and MIP. Results show that increasing fineness shortens the induction period and advances the second hydration peak by ~6 h. The cumulative heat release of the UCFA system reaches 95.2% of plain cement (85 h). Ultrafine grinding improves hydration activity and reduces total pore volume by 7.32% compared with cement and 22.18% compared with RCFA, leading to denser microstructures and higher compressive strength. Mechanistically, grinding modifies the outer sulfate-bearing layer, accelerating sulfate dissolution and early ettringite formation, while promoting CaO exposure and pozzolanic reactions. Long-term tests up to 730 days confirm that UCFA significantly reduces linear expansion, indicating improved volumetric stability. These results demonstrate that ultrafine grinding simultaneously enhances hydration reactivity and long-term stability, providing a feasible route for high-value utilization of CFB fly ash in cementitious systems. Full article

Silicon suboxide (SiO_x) has been extensively investigated as an anode material for lithium-ion batteries. However, its low electrical conductivity and significant volume expansion during cycling have hindered its practical application. Although compounding SiO_x with carbon can effectively alleviate these issues, practical challenges such as complex preparation processes and high production costs still remain. In this study, porous SiO_x/C anode materials were synthesized in a single step using residue after acid-extraction aluminum from coal fly ash (high silica slag) as the silicon source and calcium carbide as both the reducing agent and carbon source, in a NaCl-CaCl₂ molten salt medium. The intimate interface between SiO_x and carbon not only enhances the electrical conductivity of the electrode but also buffers volume expansion, while the porous structure inside the SiO_x/C particles facilitates rapid ion transport. The SiO_x/C anode fabricated from this material exhibits excellent electrochemical performance and cycling stability: the anode material synthesized at 700 °C for 3 h (denoted as SiO_x/C-700-3) retains a reversible specific capacity of 1093.58 mAh g⁻¹ after 1000 cycles at a current density of 0.4 A g⁻¹. Moreover, the optimized SiO_x/C-700-3 electrode achieves robust long-cycle stability under a high current density of 2 A g⁻¹, sustaining a reversible capacity of 486.22 mAh g⁻¹ after 800 cycles with an average Coulombic efficiency approaching 99.6%. The method proposed in this work provides a new strategy for the preparation of SiO_x/C anode materials and holds great significance for the high-value comprehensive utilization of coal fly ash and the protection of the ecological environment. Full article

Engineered cementitious composites (ECCs) reinforced with imported polyvinyl alcohol (PVA) or polyethylene (PE) fibers exhibit high tensile deformability, but the fiber cost limits the wider application of ECCs. In this study, locally produced PVA and PE fibers were used to develop lower-cost ECC, and PVA–PE fiber hybridization was adopted to improve tensile deformability. Based on matrices with various fly ash volumes, the single-fiber pullout behavior was first investigated at the micromechanical level. The results showed that PVA and PE fibers failed mainly by rupture and pullout, respectively, and that the chemical bonding between PVA fibers and the surrounding matrix decreased with increasing fly ash volume. The effects of single-fiber addition and hybrid-fiber addition on the macromechanical properties of ECC were then examined. The results indicated that ECC reinforced with hybrid PVA–PE fibers exhibited enhanced tensile performance compared with ECC reinforced with either PVA or PE fibers alone, with an ultimate tensile strain exceeding 5.3%, an average crack width below 39 μm, and hybrid reinforcing effect coefficients of 1.17–1.30, indicating a positive hybrid effect. Overall, the lower-cost ECC incorporating hybrid local fibers developed in this study demonstrates promising tensile deformability and crack-control capacity. Full article

Replacing Ordinary Portland Cement (OPC) with high volumes of fly ash (FA) offers a practical approach to reducing the environmental impacts associated with cement manufacturing and landfill disposal. However, high FA replacement levels, particularly up to 60%, often lead to lower early-age strength. This study developed a green cement mortar containing 60% FA and waste bottle glass nanoparticles (WBGNPs). The WBGNPs were incorporated at replacement levels of 2%, 4%, 6%, 8%, and 10% by volume of the OPC–FA binder. The findings showed that the addition of 4–6% WBGNPs significantly promoted the formation of dense reaction gels and enhanced compressive strength by 12.5–39.1%. Similar performance trends were observed in both the engineering and microstructural properties. The combined incorporation of FA and WBGNPs also improved drying shrinkage performance by reducing capillary stresses during water evaporation and minimizing crack development within the cement matrix. Additionally, a proposed shrinkage prediction model was validated using experimental data and demonstrated good agreement, with an average prediction error of approximately 8%. Overall, the incorporation of WBGNPs provides an effective method for producing high-volume FA cement mortars with satisfactory engineering properties suitable for concrete applications in tropical environments. This approach further supports sustainability by reducing waste generation, lowering landfill demand, and minimizing environmental pollution. 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

Fly ash substitution for cement in Portland cement concrete (PCC) has been regarded as a sustainable solution, but its widespread application remains constrained by concerns over mechanical performance and durability of PCC, especially at higher replacement rates. This study evaluates PCC mixes incorporating fly ash Type C (FA-C) or Type F (FA-F) across cement replacement rates from 10% to 90%, tracking fresh-state workability, compressive strength, and surface electrical resistivity at 7, 14, and 28 curing days. A process-based life cycle assessment (LCA) with the TRACI 2.1 method quantified global warming potential (GWP, kg CO₂/m³) under a raw-material-plus-batching-electricity boundary for each mix. A Performance Index (PI) normalizes GWP against both compressive strength and electrical resistivity, producing a performance-weighted environmental efficiency metric (GWP/PI). A sensitivity analysis across five weighting scenarios tested the robustness of mix rankings under varying priorities for structural versus ironic transport resistance performance, and a structural threshold analysis identified mixes meeting strength requirements. FA-C at 50% cement replacement exceeded the OPC control in 28-day compressive strength (42.9 vs. 36.2 MPa) and electrical resistivity (9.88 vs. 8.50 kΩ·cm), while reducing GWP by 48.3% relative to the OPC control (40.24 kg CO₂/m³). FA-F at 30–50% replacement exhibited a distinct strength–resistivity decoupling, demonstrating that strength only evaluation underrepresents the environmental efficiency of durability-critical applications. The GWP/PI metric revealed that raw GWP reduction alone misrepresents environmental efficiency. FA-C at 50% achieved a GWP/PI of 17.73, which is a 56% improvement over the OPC control. These findings question the conventional <30% substitution ceiling at 28 days under standard moisture curing and demonstrate that performance-weighted LCA metrics provide a more informed basis for sustainable concrete mix design. Full article

Concrete remains one of the most extensively utilized construction materials for buildings, bridges, and infrastructure. High-volume fly ash (HVFA) concrete has emerged as a sustainable choice to conventional mixtures, primarily due to its reduced cement demand and enhanced durability. Nevertheless, systematic investigations on the fineness fly ash contributions both for strength growth and durability performance of normal-strength HVFA concrete remain limited. The present study examines the effect of fly ash particle size, employed as a partial cement replacement, on the compressive strength and durability of normal-strength HVFA concrete. In this work, 50% of the cement by weight was substituted with fly ash of two fineness levels: passing sieve No. 200 and sieve No. 400. Twelve specimens were prepared for each mix variation, comprising compressive strength specimens (Ø15 cm × 30 cm) tested at 14, 28, and 56 days, as well as durability specimens assessed using the Rapid Chloride Penetration Test (RCPT) at 56 days. The results demonstrate that finer fly ash markedly improves compressive strength, with the highest value of 36.33 MPa recorded at 56 days for HVFA concrete comprising fly ash passing sieve No. 400. Regarding durability, increased fineness substantially reduced chloride ion ingress, as indicated by a decline in charge passed from 1845 coulombs in normal concrete to 987 coulombs in HVFA concrete with fly ash passing sieve No. 400, corresponding to a classification of very low chloride penetrability. These findings highlight the critical contribution of the fineness of fly ash in optimizing both mechanical performance and durability characteristics of HVFA concrete. Full article

In this study, an eco-friendly geopolymer concrete (GPC) was synthesized using fly ash, slag, and rice husk ash as precursors, and glass fibers were incorporated to enhance its mechanical properties. And then this study investigates the residual mechanical properties and microstructure evolution of glass fiber-reinforced geopolymer concrete (GFGPC) following elevated temperature exposure and subsequent cooling. Specimens incorporating varying glass fiber volume fractions (0–2.5%) were subjected to temperatures ranging from 25 °C to 800 °C, followed by either natural cooling or water-spraying cooling. The uniaxial compressive strength, Brazilian splitting tensile strength, and three-point flexural strength of the glass fiber-reinforced GPC were experimentally determined. Furthermore, fracture performance indicators—including the energy absorption capacity at failure, characteristic length, and double-K fracture parameters—were systematically analyzed. Results indicate that a glass fiber content of 1.5% optimally enhances the composite’s mechanical performance. Under natural cooling, splitting tensile and flexural strengths exhibit a non-monotonic trend, peaking at 200 °C. Conversely, water-spraying cooling induced thermal shock generally degrades tensile and flexural properties. However, at extreme temperatures (600 °C and 800 °C), water-spray cooling facilitates matrix densification and secondary geopolymerization, resulting in a residual compressive strength increase of 12.16% and 20.77% compared to natural cooling. Furthermore, based on composite damage theory, a binary nonlinear prediction model was developed to accurately capture the coupled effects of temperature and fiber characteristics on the residual compressive strength (R² > 0.90). Coupled with scanning electron microscopy (SEM) observations, the profound effects of elevated temperatures and thermal shock on the GPC gel matrix were elucidated, and the microscopic mechanisms underlying the failure of the fiber-bridging effect at high temperatures were thoroughly investigated. The findings of this study provide a solid theoretical foundation and scientific reference for the performance assessment and repair decision-making of GPC structures post-fire exposure. Full article

This study investigates the feasibility of incorporating high-volume municipal solid waste incineration (MSWI) fly ash into geopolymers, with a focus on its effects on mechanical performance and fragmentation behavior. A systematic experimental program was conducted in three stages. Geopolymer mixtures were first prepared with MSWI fly ash substitution rates ranging from 50% to 100% at seven distinct levels. Uniaxial compression tests were then performed to evaluate mechanical properties, followed by sieve analysis to examine fragment size distribution. The fractal dimension (D) was adopted to quantitatively characterize the degree of fragmentation. The results indicate that dry density, compressive strength, and elastic modulus all decrease progressively with increasing MSWI fly ash content. Specifically, as the fly ash content increased from 50% to 100% the compressive strength decreased from 9.57 MPa to 3.18 MPa. Notably, even at a 100% substitution rate, the compressive strength reached 3.18 MPa, which is 59% higher than the 2.0 MPa minimum requirement specified in the JTG/T F20-2015 standard. These findings demonstrate that MSWI fly ash can be effectively utilized at high replacement levels to produce sustainable geopolymers with satisfactory mechanical properties. This approach presents a viable strategy for recycling industrial solid waste into value-added construction materials. Full article

Developing sustainable and fire-resistant infrastructure is a critical technological, economic, and environmental challenge for modern construction stakeholders. Traditional cementitious composites experience severe microstructural degradation under extreme temperatures and their high carbon footprint exacerbates global environmental concerns. While the individual high-temperature behaviors of supplementary cementitious materials and fibers have been widely studied, the long-term synergistic mechanisms of high-volume fly ash combined with steel fibers under extreme thermal shock remain critically underinvestigated. To address this urgent need and bridge this scientific gap, hybrid mortars incorporating high-volume fly ash (FA) and steel fibers (SF) were tested under prolonged curing (150 days) and extreme heat (up to 600 °C). In terms of engineering and construction effects, the optimal CFA50-F hybrid composite delivered the highest residual compressive and flexural capacities (retaining nearly 60% of its late-age compressive strength at 32.00 MPa), preserved acoustic continuity (restricting UPV loss to 41.4%), and severely restricted high-temperature capillary permeability (limiting the water absorption increase to 49.7%) compared to traditional plain matrices. Scientifically, this superior resistance is governed by a two-step protective mechanism. High-volume FA chemically stabilizes the matrix by consuming vulnerable portlandite and preventing the formation of expansive calcium oxide. Simultaneously, ultra-fine FA particles physically densify the interfacial transition zones, securely anchoring the steel fibers and preventing premature high-temperature pull-out, while enabling the fibers to bridge thermally induced macro-cracks successfully. Environmentally and economically, an annualized service-life Life Cycle Assessment (LCA) revealed that substituting 50% of the cement with FA completely subsidizes the production-stage carbon penalty of the metallic reinforcement. By extending the operational lifespan to 40 years, the CFA50-F composite achieves a net 27% reduction in annualized global warming potential, providing a highly sustainable and cost-effective material solution. Full article

This study evaluates the potential of using Granulated Waste Tire Rubber (GWTR) as an alternative raw material in geopolymer mortars an eco-friendly, low-carbon alternative to traditional cement-based systems. The research investigates the synergistic effect of industrial by-products, such as slag (from ferrochrome plants) and fly ash (from thermal power plants), combined with varying proportions of GWTR (1/4, 1/3, and 1/2 by volume). A total of 22 mixtures were prepared using diverse binder pastes, including pure cement, slag-based, and fly ash-based geopolymer systems, alongside their cement-substituted derivatives. The mechanical and physical performances were assessed through compressive strength, flexural strength, and Ultrasonic Pulse Velocity (UPV) tests at 3, 7, 28, and 180 days, complemented by SEM microstructural analyses. The findings indicate that while GWTR significantly reduces the mechanical properties of pure cement matrices, this negative impact is substantially mitigated in geopolymer mortars supplemented with 5–10% cement. Mixtures containing 1/4 GWTR with 90–95% slag or fly ash (M6, M7, M15, M16) yielded the most successful results in terms of both strength and sustainability, specifically, mixtures M7 and M16 because the hybrid binder synergy effectively compensated for the rubber-induced porosity, ensuring a denser matrix and structural-grade compressive strength alongside high sustainability. Significant decreases in performance were observed at higher GWTR ratios, particularly at the 1/2 level. Overall, the study demonstrates that integrating GWTR into optimized geopolymer systems offers a viable pathway for the valorization of environmental waste and minimizing the ecological footprint of the construction industry. Full article

Red mud (RM), a waste residue from alumina extraction, poses serious environmental impacts on water resources, land resources, and ecological systems due to its large production, high alkalinity, and low resource utilization. To enhance the overall utilization rate of RM solid-waste materials, this study focuses on RM, blast furnace slag (BFS), and fly ash (FA) cementitious materials as the research objects. Through mechanical tests and microstructural analysis, the optimal mix ratio of the ternary RM-based cementitious material is determined, and a systematic study of its microstructural evolution is conducted. Concurrently, fractal theory was used to quantify the microstructure of the material, revealing the evolution laws of the mechanical properties of ternary red-mud-based cementitious materials from a mesoscopic perspective. The results indicate that reducing the proportion of RM or slag alone to increase the FA content yields inferior modification effects compared to simultaneously reducing the proportions of both RM and BFS to increase FA content. Compared with the binary RM-based cementitious material made of RM and BFS, the 28-day compressive strength increases by approximately 25%, reaching 50 MPa. The incorporation of FA can reduce the volume of harmful pores in the cementitious matrix, providing ample reactive material for subsequent hydration reactions, promoting later hydration products, and improving the distribution of the internal pore structure. This leads to increases in both fractal dimensions, and a rational mix proportion can effectively improve the microstructure and mechanical properties of the ternary RM-based cementitious material. 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