Search Results (723)

In this study, the effect of substituting waste glass aggregate and recycled concrete aggregate (RCA) at different ratios (20%, 40%, 60%, 80%, 100%) on the compressive strength performance of geopolymer concretes reinforced with tire-derived textile fibers (TDTF) was investigated. A total of 22 different mixtures were prepared, and their 7-day and 28-day compressive strengths, water absorption rates, and ultrasonic pulse velocity (UPV) were determined. The results showed that TDTF improved compressive strength in both waste aggregate series, with a more pronounced contribution at 28 days. Increasing the waste glass aggregate content reduced 28-day compressive strength by 16–31% compared with the control mixture, whereas RCA mixtures showed only 1–4% strength loss up to 60% replacement and 17–19% loss at higher replacement levels. Glass aggregate mixtures generally exhibited higher early-age strength, while RCA mixtures performed better at 28 days. TDTF addition increased the 28-day compressive strength by approximately 25–30%, depending on aggregate type and replacement level. The lowest water absorption value was obtained in the fiber-reinforced glass aggregate series, whereas the highest value was measured in the RCA series, mainly due to the porous adhered mortar on RCA particles. Based on the compressive strength, water absorption, and UPV results, RCA replacement levels up to 60% and glass aggregate replacement levels of 40–60% may be considered suitable for the mixtures examined in this study. Full article

The successful realization of a circular economy in the cement industry, coupled with a substantial reduction in carbon emissions, relies on the development of sustainable alternative binder systems. This study investigated the physicomechanical performance and sulfate resistance of composites produced by alkali activation of natural perlite and blast furnace slag. The aim of the research was to improve mechanical properties under low- and medium-alkalinity conditions (5–10 M NaOH). The samples were cured at an ambient temperature of 20 °C and then treated with heat at 60 °C. These samples were then mechanically processed and subjected to five soak–dry cycles in 5% and 10% Na₂SO₄ solutions. The results showed that heat treatment resulted in the formation of a dense C-A-S-H gel, increasing compressive strength approximately eightfold, from 11.64 MPa to 92 MPa. However, perlite’s porous and brittle structure limits its flexural strength to 0.27 MPa; this value is insufficient for structural applications. Under severe sulfate attack (10% Na₂SO₄), samples cured at ambient temperature showed a 12% mass increase in the first cycle due to solution infiltration into capillary voids. As a consequence of extensive ettringite and gypsum formation, the specimens experienced severe deterioration, resulting in a complete loss of mechanical integrity and a residual compressive strength of 0 MPa. In contrast, heat-treated samples showed limited ion diffusion due to a denser matrix and an improved aggregate interface transition zone, resulting in a 2.6% mass increase and a residual compressive strength of 5.17 MPa. Consequently, the obtained findings indicate that thermally treated alkali-activated slag–perlite composites exhibit high resistance against sodium sulfate attack and may have potential for use in specific industrial environments with high sulfate concentrations. However, the performance of these materials under more complex aggressive conditions, such as mining environments involving magnesium sulfate exposure and acidic drainage waters, should be further validated through future studies. Full article

The development of sustainable grouting materials is essential for enhancing underground strata stability while reducing the environmental impact associated with ordinary Portland cement (OPC). This review summarizes previously published studies on alkali-activated grouting materials (AAGMs) prepared using fly ash (FA) and ground granulated blast furnace slag (GGBFS), activated by sodium hydroxide and sodium silicate solutions. A comprehensive literature-based analysis was conducted to evaluate both fresh and hardened properties, including fluidity, setting time, yield stress, compressive strength, and durability-related performance. Particular attention was given to the influence of FA-GGBFS proportions and activator composition on rheological behaviour, mechanical performance, and engineering applicability. The reviewed studies indicate that increasing GGBFS content significantly accelerates geo-polymerization and setting behaviour and enhances early-age strength development due to its higher calcium reactivity. In contrast, FA contributes to improved workability and flowability, attributed owing to its spherical particle morphology and slower reaction kinetics. The reviewed literature further suggests that balanced FA–GGBFS alkali-activated systems can provide a favourable combination of fluidity, injectability, setting behaviour, and mechanical performance, making them particularly suitable for underground grouting and rock mass reinforcement applications. Compared with conventional OPC-based grouts, AAGMs demonstrate superior mechanical performance together reduced environmental impact through the utilization of industrial by-products and reduced clinker consumption. However, several critical challenges still hinder the large-scale implementation of alkali-activated grouting materials in underground mining, particularly with respect to field-scale validation, shrinkage mitigation, safe handling of alkaline activators, and the current lack of standardized specifications and design guidelines for underground grouting applications. These findings provide a robust scientific basis for the design and application of eco-efficient grouting materials in deep underground mining environments and support the advancement of sustainable practices in underground engineering. Full article

This study aims to explore the preparation process and properties of unburned lightweight aggregate using red mud synergistically with fly ash, granulated blast-furnace slag, and other multi-source solid wastes. Curing regimes and alkali-activated systems were controlled. Their effects on physical properties and environmental safety of lightweight aggregate were systematically evaluated. Results show that curing temperature and alkali activator exert significant synergistic effects on physical properties of lightweight aggregates. Steam curing performs better than standard curing. Performance improves with increasing steam temperature. Sodium silicate solution with a modulus of 1.0 is determined as the optimal activator. Under 90 °C steam curing, Sample D2 achieves the best overall performance. Its cylinder compressive strength reaches 6.92 MPa. 1 h water absorption is 14.8%. Softening coefficient is 0.93. Porosity is as low as 31.07%. Microscopic analysis reveals that higher curing temperature significantly accelerates the hydration reaction of the RMLWA system. It promotes the formation of abundant cementitious products such as C-S-H gel. These products fully fill internal pores and microcracks of the aggregate. A dense three-dimensional network skeleton structure is finally formed. For environmental safety, heavy metal leaching concentrations of steam-cured samples are generally lower than those of standard-cured samples. This study realizes high-value resource utilization of industrial solid wastes. It also provides a new technical route for the development of green building lightweight aggregate. Full article

This study evaluated the effects of copper slag (CS), dosed relative to the mass of fly ash (FA; CS = 0, 7.5, 15, and 22.5%), and the volume fraction of hybrid steel fibers (V_f = 0.0, 0.5, and 1.0%) on the mechanical response of an alkali-activated geopolymer composite. The tests were performed using a two-factor CS × V_f design (4 × 3), with compressive strength (f_c) and splitting tensile strength (f_ct.sp) determined as the response variables. Statistical analysis showed significant effects of CS, V_f, and CS × V_f on f_c, and a significant CS × V_f interaction for f_ct.sp, confirming that the fiber effect depended on the CS content. The greatest increases in f_c relative to fiber-free composites were obtained for CS = 7.5%: +73% (V_f = 0.5%) and +102% (V_f = 1.0%), and for CS = 22.5%: +75% (V_f = 1.0%). For f_ct.sp, a decrease was found at CS = 0% and V_f = 0.5% (−34%), whereas an increase was observed at CS = 22.5% and V_f = 1.0% (+49%). The interpretation of the mechanical response was extended by DIC-based strain analysis in compression and splitting tests, together with σ_ct.sp–ε_x curves, indicating differences in strain/damage localization and post-cracking response. Full article

Infrastructure maintenance and emergency repairs require rapidly setting cementitious materials, yet conventional cement presents issues of high energy consumption and substantial CO₂ emissions. Addressing this challenge, this research has developed a ternary alkali-activated cementitious material (CGFM) composed of calcium carbide residue (CCR), granulated blast furnace slag and fly ash. This study separately investigates the effects of CCR content (0–10%), alkali content (6–12%) and activator modulus (1.0–1.5) on workability and early mechanical strength. The hydration mechanism was examined through X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), Thermogravimetry-Derivative Thermogravimetry (TG-DTG) and Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) analysis, whilst life cycle assessment was employed to quantify the ecological impacts. Results indicated that a 3% CCR dosage significantly improved the gel structure, achieving a 7-day compressive strength of 69.8 MPa and a 37% increase in flexural strength. At a CCR dosage of 3%, alkali content of 8%, and modulus of 1.4, CGFM achieved a peak compressive strength of 80.2 MPa by the seventh day. This performance is attributable to its substantial gel content and high degree of polymerisation, which results in a dense structure. Life cycle assessment confirmed that compared to sulphoaluminate cement mortar, CGFM mortar reduced CO₂ emissions by 64.6% and energy consumption by 48.6%. Full article

Dredging projects associated with China’s expanding maritime transportation and waterway regulation produce substantial volumes of dredged soil each year. This dredged soil, characterized by poor engineering properties, cannot be directly used for filling projects and requires improvement. On the other hand, the use of solid waste curing agents to replace traditional curing agents for semi-curing improved dredged soil can achieve the goal of treating waste with waste. This study employs a CGF curing agent composed of calcium carbide slag, blast furnace slag, and fly ash for the semi-curing improvement of dredged soil. The impact of the curing agent content on the compaction properties of semi-cured improved dredged soil is investigated. Additionally, through freeze–thaw cycle tests and microscopic experiments, the influence of the number of freeze–thaw cycles on the strength of semi-cured improved dredged soil and its microscopic mechanism are examined. The results indicate that as the curing agent content increases, the maximum dry density of the CGF semi-cured improved dredged soil decreases, while the optimal moisture content increases. Under freeze–thaw cycles, both the mass and unconfined compressive strength of the CGF semi-cured improved dredged soil decrease with an increasing number of cycles. Microscopic test results show that alkali-activated products (C-S-H, C-A-S-H, C-A-H) cement soil particles, fill soil pores, and enhance the internal stability of the soil. However, as freeze–thaw cycles progress, the structure of the CGF semi-cured improved dredged soil is gradually damaged. The enlargement of pores and the formation of penetrating cracks and voids lead to a reduction in strength. Increasing the curing agent content can effectively improve the frost resistance of the CGF semi-cured improved dredged soil. Full article

Granulated blast furnace slag is a commonly used supplementary cementitious material in cement-based materials. The raw materials for ironmaking and the cooling process affect its composition, thereby influencing its reactivity. Three types of slag were selected and incorporated at replacement ratios of 15%, 30%, and 50% to investigate the influence of chemical composition on the activity index of slag at different ages and the mechanisms. The results indicate that in the early hydration stage, slag primarily plays a mechanical filling and dilution role (inert volumetric occupation without significant heterogeneous nucleation), while the pozzolanic effect dominates at later stages. Al₂O₃ in the slag is activated at early ages to form ettringite; at replacement ratios of 30%, C-A-S-H gel is also formed at later ages; when the replacement ratio reaches 50%, the significant reduction in cement clinker content leads to dropping in system alkalinity—corresponding to a 50% reduction in cement-derived Ca(OH)₂, the activation of Al₂O₃ in the slag is not significant at early ages. The effects of glass content, alkali content, specific surface area, CaO + MgO content, quality coefficient, and basicity coefficient on the reactivity become prominent at longer ages. No additional crystalline phases beyond those present in pure cement paste were detected in the cement paste after slag incorporation. This study provides a theoretical basis and data support for the high-value utilization of industrial solid waste in green building materials. Full article

Sodium sulfate-activated slag cement is considered a highly promising low-carbon cementitious material; however, its application is limited by low early-age activation efficiency and slow strength development. This study aims to systematically elucidate the coupled regulatory mechanism of alkalinity (2% and 4% Na₂O equivalent) and sodium sulfate dosage on the performance of alkali-activated slag (AAS). Under standard curing conditions (20 ± 2 °C, relative humidity ≥ 95%), the macroscopic properties of the samples (workability, setting time, and compressive strength) and the evolution of their microstructure (analyzed by XRD, FTIR, and SEM-EDS) were evaluated. The results indicate that the effect of sodium sulfate on alkali-activated slag (AAS) strongly depends on the alkalinity. Under low-alkalinity conditions (2% Na₂O), sodium sulfate exhibits a synergistic activation effect by increasing the ionic concentration, promoting slag depolymerization and the nucleation of ettringite (AFt). Specifically, compared with the control, incorporating 6 wt% sodium sulfate (N2S6 mix) increased compressive strength by approximately 82% at 3 days and 21% at 28 days. In contrast, under high-alkalinity conditions (4% Na₂O), excessive sodium sulfate (≥2 wt%) shows an inhibitory effect. This is likely because an excess of sodium sulfate interferes with the normal polymerization pathways of the aluminosilicate network, suppressing the formation of the primary C-(A)-S-H gel and thus significantly reducing later-age strength. Microstructural analysis revealed that the hydration products in the composite-activated system mainly consist of C-(A)-S-H gel, ettringite (AFt), monosulfate (AFm), and hydrotalcite. This study investigates the observed kinetic trends of anion-competitive hydration under different alkalinity conditions, providing a theoretical basis for the mix design of low-carbon alkali-activated materials and the valorization of coal chemical industrial salts. Full article

In recent years, there has been an urgent need for integrated solutions to synergistically manage industrial solid waste stockpiling and CO₂ emissions. Single-component solid waste mineralization, such as those using only fly ash (FA) or carbide slag (CS), often encounters performance bottlenecks, typically characterized by a compressive strength of less than 2 MPa and a carbonation efficiency of under 10%. Furthermore, a systematic quantitative understanding of the synergistic interactions within multi-component systems remains absent. This study employs Response Surface Methodology to investigate the interactive effects of solid waste ratios, the water-to-solid ratio, and alkali content, aiming to elucidate the synergistic mineralization mechanism and overcome the bottlenecks of single solid waste mineralization. Under optimized conditions—specifically, 34% CS, 30% phosphogypsum (PG), a water-to-solid ratio of 0.48, and an alkali content of 27%—the system achieved a 7-day compressive strength of 3.5 MPa and a CO₂ mineralization efficiency of approximately 16%, representing a significant improvement over typical single solid waste mineralization materials. Microstructural and spectroscopic analyses indicate that CS serves a dual function as both a calcium source for CaCO₃ precipitation and an alkaline activator for FA. FA constructs a dense aluminosilicate network via pozzolanic reactions, while SO₄²⁻ released from PG promotes the formation of ettringite, facilitating efficient pore filling and early strength development. Additionally, it was observed that surface pores were filled with more products compared to the interior, forming a gradient pore structure that is dense on the outside and sparse on the inside. The AFt and silicate gel were identified as the key microstructural driver for the performance enhancement. This study not only explores the ternary synergistic mechanism of FA, CS, and PG but also provides a viable pathway for developing high-performance solid waste-based mineralization materials that combine mechanical properties with efficient CO₂ sequestration. Full article

This study presents a comprehensive assessment of high-temperature performance, economic viability, and environmental sustainability of alkali-activated slag paste (AASB) incorporating municipal solid waste incineration bottom ash (MSWI-BA). The research systematically evaluates the effects of MSWI-BA content (0–12%), alkali content (2–6% Na₂O equivalent), water glass modulus (Ms = 0.75–1.75), and activator type on key performance metrics, both resource recovery and carbon reduction goals. Results show that the optimized formulation (6% MSWI-BA, 4% Na₂O, Ms = 1.5) achieves superior high-temperature resilience, retaining 76% of its initial compressive strength after 800 °C exposure—a stark contrast to OPC, which undergoes near-complete strength loss. Economic analysis reveals that while MSWI-BA offers an 88% reduction in raw precursor cost, the optimized AASB incurs a modest 3.7% total material cost premium over OPC, which is offset by its long-term sustainability benefits. Furthermore, a life-cycle assessment demonstrates that AASB has a 66.95% lower carbon footprint than OPC. Full article

The copper industry generates nearly 25 million tons of slag annually, which is stockpiled or landfilled, leading to land occupation and the potential for soil and water contamination alongside the environmental burden of the construction sector, which accounts for up to 9% of global CO₂ emissions and massive raw material consumption. The need for low-carbon, resource-efficient binders has spurred interest in geopolymerization, or the alkali activation of aluminosilicate residues, as a pathway to valorize industrial by-products. The objective of this review is to analyze, synthesize, and critically evaluate the scientific evidence on alkali-activated materials derived from Cu slag, emphasizing the synthesis parameters, mechanical and durability behavior, and environmental performance. The review applies the PRISMA 2020 methodology. The analysis of the 57 reports shows that copper slag—used alone or with metakaolin or blast furnace slag—can produce alkali-activated materials with high compressive strength, refined pore structures, and cradle-to-gate CO₂ reductions of up to 80%. Cu slag is not a chemically homogeneous precursor, and its influence on performance depends on the activation strategy and dosage rather than the slag content alone. Overall, this review consolidates dispersed findings, identifies research gaps, and proposes a framework for sustainable valorization in the form of low-carbon construction materials. Full article

Although geopolymer and alkali-activated binders are promoted as low-carbon OPC alternatives, their resource-centric performance remains complex and geographically dependent. This review examines these systems from a resource-efficiency perspective and evaluates alkaline activator demand; precursor availability, including fly ash, slag, calcined clays, and mining residues; and embodied energy across mix designs and curing regimes. Recent mechanical and durability analyses, together with life cycle assessments, reveal important trade-offs in alkali-activated geopolymer systems. Customized precursors may unintentionally compromise their inherent resource efficiency, while the declining availability of industrial waste increasingly competes with alternative waste valorization processes. Developing one-part activator systems and implementing data- or machine-optimized mix designs capable of handling extremely highly variable waste streams will be necessary to achieve meaningful reductions in mineral consumption, energy demand, and emissions. The study reframes these binders as enablers of urban mining and industrial symbiosis. Policy changes toward resource-oriented governance, including performance-based standards, carbon-responsive procurement, and more transparent end-of-waste legislation, are also needed to promote a circular material economy. Strategic, large-scale deployment requires the integration of regional resource mapping with predictive performance modeling to navigate resource constraints in the construction sector. Full article

Clinker-free binders derived from industrial solid wastes are promising for low-carbon construction, but many binder designs still rely on reagent-grade activators. This study investigates carbide slag (CS) as a substitute for a conventional alkali activator route in a waste-derived clinker-free binder composed of fly ash, coal gasification slag, and blast furnace slag. The CS-based binder is benchmarked against unactivated, mechanically processed, and Ca(OH)₂-activated reference binders. The CS-based route shows sustained strength development from 3 to 28 d and achieves 20.04 MPa compressive strength at 28 d, slightly higher than the Ca(OH)₂-activated reference (18.78 MPa). Mercury intrusion porosimetry reveals clear pore refinement: the fraction of pore throats ≤ 50 nm increased to 40.96% in the CS-based binder, compared with 1.50% in the unactivated milled-CGS reference, and the median pore throat decreased to 70.01 nm. Calorimetric kinetic fitting showed that the CS-based binder had a higher fitted cumulative heat release, 58.75 J·g⁻¹, than the Ca(OH)₂-activated reference, 23.36 J·g⁻¹, indicating a more sustained reaction process. FTIR, TG-DTG, XRD, and SEM-EDS further supported differences in gel development and Ca-bearing phase evolution. In particular, the CS-based binder showed a high-temperature mass loss above 600 °C of 14.11%, compared with 5.83% for the Ca(OH)₂-activated reference, and a stronger relative calcite signal. These results show that CS substitution is not equivalent to simple Ca(OH)₂ addition and provides binder-scale evidence for designing waste-derived clinker-free binders with reduced reliance on reagent-grade activation. Full article

Copper slag (CS) was considered a major by-product produced from the copper refining industry, which estimates about 2.2 to 3 tons generated during the production of every one ton of copper. At the same time, continuous dumping and improper disposal of this byproduct have led to serious environmental problems, especially due to the leaching of heavy metals into soil and water. This review carefully studies the potential of CS as a sustainable construction material through a clear distinction of its performance, especially when used as a fine aggregate and as a supplementary cementitious material (SCM). Due to the presence of higher content of iron and silica, higher hardness, and very low water absorption, it was found that CS helps in improving the density and durability of concrete. When used as a fine aggregate, CS enhances workability, strength, and durability at an optimum level of about 40%, mainly due to better particle packing and reduced pore connectivity. On the other hand, when used as an SCM, CS contributes to long-term strength through pozzolanic reactions and the formation of C–S–H gel, but its replacement level should be limited to about 20% to avoid loss of early-age strength caused by reduced alkalinity. In terms of durability, the use of CS can reduce water absorption by up to 60%, lower chloride penetration, and improve resistance to sulfate attack. Environmental Life Cycle Assessment studies show that CS can reduce global warming potential by about 12–19% and also decrease overall energy consumption. Statistical validation using multi-criteria decision analysis (MCDA) and separate regression modeling with an R² value of about 0.965, which supports these optimum replacement levels up to 40% for fine aggregate and 20% for cement, providing a good balance between strength, durability, environmental benefits, and cost. Overall, this review shows that CS is a valuable and multi-functional material that supports circular economy practices when used with a proper mix design based on specific applications. Full article