Search Results (649)

The paradigm of sustainable development, coupled with contemporary inclinations towards green construction, exerts a considerable effect on the evolution of environmentally benign building composites. The main aim of this study is to create geopolymer composites with improved physical and mechanical properties. An examination of the properties of a geopolymer composite (GS), using ground granulated blast furnace slag (GGBFS) and plant fibers, is presented in this paper. Sisal (SF) and flax (FF) fibers, along with their combination (SF + FF), were integrated into the slag at concentrations of 0%, 0.5%, 1.0%, 1.5%, and 2% by weight. Before use, plant fibers were treated with a 5% NaOH solution. The geopolymer composites (GC) underwent evaluation for their density, compressive and flexural strengths, and water absorption characteristics. Scanning electron microscopy was employed to examine the fracture characteristics of the GC. The compressive and flexural strengths of GC were improved by including 1% SF, FF, and their combination, 0.5% SF + 0.5% FF. Compressive strength increases were 11.5%, 8.6%, and 14.5%, while flexural strength increases were 17.4%, 13%, and 19.6%, respectively. Water absorption of GC with 1% SF, FF, and SF + FF decreased by 14.6%, 10.8%, and 20.4%, respectively. The apparent synergistic performance of hybrid sisal-flax reinforcement at a total fiber content of 1% was revealed. GCs at the fracture have a homogeneous rough structure with microcracks and accumulations of geopolymer reaction products. The matrix-plant fiber interface in GC is identified by a rounded region with elongated fibers, indicating the fiber’s performance under mechanical stress. The findings of this investigation suggest the feasibility of utilizing plant fibers in environmentally sound geopolymer construction composites. Full article

Use of fly ash (FA), a by-product of coal-fired power stations, and basic oxygen furnace slag (BOFS), a by-product of steel production plants, in construction applications in Kazakhstan is limited due to their low quality and inherent problematic properties. For example, the concern with using BOFS as an aggregate in concrete is the volume expansion caused by the formation of calcium hydroxide (Ca(OH)₂) or magnesium hydroxide (Mg(OH)₂) in the concrete matrix generated by a chemical reaction between water and free calcium oxide (f-CaO) or free magnesium oxide (f-MgO) in BOFS. This issue can be addressed through geopolymerization and CO₂ curing (mineral sequestration). Moreover, the quality of FA does not meet ASTM Class F FA criteria (coarse particle sizes and low reactivity). This study investigated the physical, mechanical, microstructural, and durability properties of geopolymer mixtures composed of low-quality FA, ground granulated blast-furnace slag (GGBFS), and BOFS aggregates under various curing conditions. Six distinct curing regimes were assessed: air, water, 6 h steam, 12 h steam, 6 h steam combined with 6 h CO₂, and 6 h steam combined with 12 h CO₂ curing. The hardened properties, durability, and microstructural characteristics of geopolymer mixtures were mainly assessed by compressive strength, dielectric constant (DC), drying shrinkage, expansion (1 M NaOH solution and water expansions), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) images. Test results show that steam curing and combined steam and CO₂ curing significantly enhanced the performance of the mixtures containing BOFS aggregates. The combined steam and CO₂ curing accelerated the mineral sequestration of f-CaO in the BOFS aggregates, increasing the 28-day compressive strength by up to 27.7% and 19.2% (reaching 37.1 MPa) compared to air- and water-cured mixtures (29.1 and 31.1 MPa, respectively). While air (20.0 and 11.7), steam (28.7 and 12.4), and combined steam and CO₂ (23.6 and 12.6) curing at 1-day and 182-day yielded lower DC, water curing (30.5 and 32.2) had higher DC. The extended steam and CO₂ curing times further enhanced compressive strength growth (39.6 MPa) by 36.6% for air-curing and 27.1% for water curing, although curing duration did not significantly affect the dielectric constant. Importantly, the expansion of the BOFS aggregate in both water and 1 M NaOH solution was minimized up to 0.04% under combined curing, mitigating the inherent volumetric instability of the BOFS. Drying shrinkage was also reduced by 0.17% under combined curing conditions. Longer steam and CO₂ curing times reduced variability in dielectric constant, drying shrinkage, and the expansion characteristics. FTIR spectroscopy, SEM image, and XRD analyses confirmed that the mixture’s geopolymerization was more noticeable during the steam and CO₂ curing regimes than during water and air curing regimes. The longer steam and CO₂ curing times promoted extended hydration and the formation of stable carbonate compounds from the BOFS f-CaO, producing a significantly denser and microstructurally stable geopolymer matrix. Full article

To address the high carbon emissions generated during the production of cement, lime, and other traditional soil stabilizers and to promote the resource utilization of industrial solid waste, this study proposed a low-carbon loess stabilization scheme using tuff powder (TP), fly ash (FA), and ground granulated blast-furnace slag (GGBS) activated by alkaline solutions to fully substitute conventional cement and lime. A series of macroscopic tests, including unconfined compressive strength, water immersion, and triaxial shear tests, were carried out on stabilized loess. Combined with microcharacterization including X-ray diffraction (XRD), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) spectroscopic testing, this study systematically evaluated the mechanical performance, water stability, and microstructural evolution of stabilized loess and quantified its global warming potential (GWP). Macroscopic test results reveal that the composite binder consisting of 15% multi-source solid waste (TP:FA:GGBS) = (1:1:3), 3% NaOH, and 3.2% Na₂SiO₃ (relative to solid waste mass) delivers the optimal comprehensive performance of stabilized loess. Alkali activation significantly accelerates early strength development, and both compressive and shear strengths are markedly improved compared with samples treated solely with solid waste. Furthermore, decreasing the activator modulus further enhances mechanical properties and water resistance. Microscopic characterizations demonstrate that alkali activation stimulates the pozzolanic reaction of active components in solid waste, generating cementitious gels that bind soil particles and unreacted solid waste to form dense network matrices. As a fine filler, TP also acts as a nucleation sites for hydration product crystallization, which facilitates the formation of cementitious phases. Full article

Recycled aggregate concrete (RAC) offers an effective approach to reducing the environmental burden associated with construction and demolition waste. In this study, a fiber-reinforced RAC was developed by replacing part of the cement with fly ash and ground granulated blast-furnace slag, while glass fibers or basalt fibers were incorporated as reinforcing materials. A systematic experimental program was conducted to evaluate the mechanical behavior of the proposed concrete under different saturation conditions. The results show that the best toughness performance was achieved in the natural moisture state. In comparison, compressive and flexural strengths reached their maximum values under dry conditions, whereas splitting tensile strength peaked in the natural state. Based on the experimental data, prediction equations were established for the splitting tensile and flexural strengths by considering both saturation degree and fiber content. A stress–strain model under uniaxial compression was also developed. In addition, scanning electron microscopy (SEM) was employed to examine the fiber–matrix interface and hydration products, thereby clarifying the microstructural characteristics of the concrete at different saturation levels. Full article

This PRISMA-guided scoping review examines the use of waste materials in civil engineering as a sustainable approach to reducing environmental impacts, conserving natural resources, and supporting circular economy principles. The rapid growth of urbanization, industrialization, mining, and agricultural activities generates large amounts of waste materials, including fly ash, ground granulated blast-furnace slag, bauxite residue, mining tailings, waste rock, acid-mine drainage sludge, waste plastics, post-consumer vulcanized rubber, recycled construction materials, and agricultural ashes. The disposal of these materials often creates serious environmental and land-use problems, making their reuse increasingly important. In this context, civil engineering is one of the most promising sectors for large-scale waste valorization because of its high material demand and its ability to use different waste streams into practical applications such as concrete and cementitious systems, pavement and asphalt engineering, geotechnical works, and other infrastructure sectors. This review critically evaluates the global availability, material characteristics, engineering applications, environmental and economic benefits, recent advances, and key challenges related to major industrial, mining, agricultural, polymeric, and construction-derived wastes. Although significant progress has been made in this field, wider implementation is still limited by variations in material properties, technical and environmental challenges, economic constraints, and limited field validation of long-term performance. By bringing together current knowledge from different waste streams and civil engineering sectors, this review highlights important research gaps and future directions to support more sustainable, resilient, and resource-efficient infrastructure development. The effective use of waste materials in civil engineering can play an important role in reducing carbon emissions, improving resource efficiency, and supporting global sustainability. Full article

To address the problems of high moisture content, fine particle size, and limited conventional reutilization of stainless steel slag mud (SSSM), controlled low-strength material (CLSM) was prepared using SSSM as the primary solid component and cement together with ground granulated blast furnace slag (GGBS) as cementitious materials. The effects of GGBS replacing cement and SSSM, respectively, on the properties of CLSM and their variation patterns were investigated. Its solidification mechanism was analyzed through simulated control tests, X-ray diffraction (XRD), thermogravimetric–differential thermogravimetric analysis (TG-DTG), and scanning electron microscopy (SEM). The results show that, when GGBS replaces cement, the water-to-solid ratio and bleeding rate increase, while the compressive strength at all curing ages decreases overall; however, the 28 d strength still meets the requirement for CLSM. When GGBS replaces SSSM, the water-to-solid ratio and bleeding rate increase with GGBS fraction, and the compressive strength at all curing ages increases overall. At a GGBS fraction of 18%, the water-to-solid ratio reaches 0.363, the bleeding rate reaches 5%, and the 28 d and 60 d compressive strengths reach 7.3 and 11.2 MPa, respectively, representing increases of 23.3 and 21.4 times compared with the system without GGBS (0.3 and 0.5 MPa). The simulated SSSM substitution tests show that a synergistic solidification effect exists between SSSM and GGBS and contributes to strength development. Microstructural analysis shows that GGBS undergoes hydration under the alkali–sulfate environment provided by SSSM, generating ettringite (AFt) and calcium silicate hydrate (C-S-H gel), which fill pores and thereby enhance strength, while calcium hydroxide (Ca(OH)₂) provides an alkaline environment and promotes the participation of potentially active components in SSSM in the synergistic solidification process. Full article

This study investigated the effects of precursor type, NaOH molarity, and thermal curing temperature on the performance of geopolymer mortars produced using fly ash (FA), ground granulated blast-furnace slag (GBFS), metakaolin (MK), and waste brick powder (WBP). Mortars were activated using 12 M and 16 M NaOH solutions at a constant Na₂SiO₃/NaOH ratio and thermally cured at 60 and 90 °C for 24 h. Physical, mechanical, transport, microstructural, and cost-performance properties were evaluated. The results demonstrated that the optimum activation conditions strongly depended on precursor type. MK-based mortars cured at 16 M–90 °C exhibited the best overall performance, achieving the lowest apparent porosity (6.1%) and water absorption (5.4%), and the highest oven-dry density (2194 kg/m³), compressive strength (25.8 MPa), and flexural strength (3.43 MPa). These mortars also exhibited the lowest capillary water absorption (1.88 kg/m²), the highest electrical resistivity (248.00 kΩ·cm), and the lowest charge passed (177 C), indicating enhanced pore refinement and chloride-ion penetrability. In contrast, GBFS performed better under milder activation conditions, whereas WBP showed lower performance due to its coarser, more crystalline structure. SEM/EDS analyses confirmed that the formation of dense aluminosilicate gel governed matrix quality and overall performance. Overall, MK activated at 16 M and cured at 90 °C provided the most favorable balance between technical performance and cost efficiency. Full article

In order to conduct a comprehensive investigation into the effects of ground granulated blast furnace slag (GGBFS) on the dynamic mechanical properties and mesoscopic damage mechanisms of recycled aggregate concrete (RAC), a combined approach integrating material testing, microscopic characterization techniques, and theoretical analysis was adopted in this study. Two GGBFS replacement rates (0% and 35%) were considered. Uniaxial compression tests were performed to obtain data at different curing ages (T = 7 d, 28 d, 56 d, and 150 d) and strain rates ($\dot{\epsilon }$ = 10⁻⁵/s, 10⁻⁴/s, 10⁻³/s, and 10⁻²/s). The obtained data were complemented by nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) analyses to characterize the evolution of the microstructure and pore characteristics of the specimens. The findings demonstrated that prolonging the curing period continuously densified the microstructure of the specimens, resulting in a commensurate improvement in their initial macro-mechanical behavior. At curing ages exceeding 28 d, the secondary hydration reaction of GGBFS was found to generate additional C-S-H gel, which filled the internal microvoids within the specimens, reduced porosity, and further improved the initial macroscopic mechanical properties. Concurrently, the microstructural characteristics observed at different curing ages, in conjunction with the crack propagation and the fracture toughness effects associated with strain rate, further influenced the initiation, propagation patterns and paths of microcracks during uniaxial compression, as well as the adjustment of the effective stress framework. Furthermore, characteristic parameters describing the evolution of mesoscopic fracturing and yielding damage exhibited regular variations with curing age and strain rate. For specimens cured for 56 d, compared to those with a GGBFS replacement rate of 0%, specimens containing 35% GGBFS exhibited a 4.13% increase in peak stress and a 0.29% decrease in peak strain at $\dot{\epsilon }$ = 10⁻⁵/s. At a replacement rate of 35%, as the strain rate increased from $\dot{\epsilon }$ = 10⁻⁵/s to $\dot{\epsilon }$ = 10⁻²/s, the peak stress rose from −50.37 MPa to −60.74 MPa, whereas the peak strain dropped from −23.87 × 10⁻⁴ to −22.15 × 10⁻⁴. This study provides significant scientific evidence and a theoretical framework for the engineering application of GGBFS-modified RAC under varying strain rate conditions. Full article

Magnesium slag (MS), an important industrial solid waste generated during the magnesium production process, is recognized for its considerable potential to reduce carbon emissions and advance sustainability in the building materials industry. However, its widespread application is severely hindered by volume instability, which is primarily attributed to the delayed hydration expansion of free calcium oxide and free magnesium oxide. In this review, the physical and chemical properties of magnesium slag are systematically summarized, and the underlying mechanisms responsible for the volume instability of MS-based cementitious materials are critically elucidated. Furthermore, targeted strategies for improving volume stability are focused on and evaluated, including the acid treatment of magnesium slag for oxide passivation and the collaborative utilization with complementary solid wastes such as ground granulated blast furnace slag, steel slag, and fly ash. Through this critical synthesis, a framework is established for overcoming the soundness bottleneck, thereby repositioning magnesium slag as a viable and reliable constituent in next-generation sustainable building materials. Full article

Ordinary Portland cement (OPC) production contributes approximately 7–8% of global anthropogenic CO₂ emissions, driving urgent demand for clinker-efficient binders utilizing industrial by-products. Flue gas desulfurization (FGD) gypsum and ground granulated blast-furnace slag (GGBFS) represent underutilized industrial by-products with documented potential as supplementary cementitious materials. This study investigates the mechanical, durability and microstructural performance of OPC–GGBFS–FGD gypsum ternary concrete mixtures incorporating untreated flue gas desulfurization (FGD) gypsum at 0–20% of total binder mass and ground granulated blast-furnace slag (GGBFS) at 25–50% of total binder mass in M30 structural concrete (w/b = 0.45). Compressive, split tensile and flexural strengths were evaluated at 7–90 days alongside rapid chloride penetration (RCPT), water absorption, strength efficiency index (SEI) and SEM–EDX analyses. Binary GGBFS replacement progressively enhanced long-term compressive strength, with T35F0 attaining 55.6 N/mm² at 90 days (+33.7% relative to the OPC control). Moderate FGD gypsum contents (5–10%) further enhanced overall performance. Among all mixtures, T50F10 exhibited the best overall performance on the mechanical and durability indicators evaluated, achieving 54.2 N/mm² compressive strength at 90 days together with a rapid chloride permeability value of 410 C, corresponding to ‘Very Low’ chloride ion penetrability. Beyond 10% FGD gypsum, progressive multi-parameter deterioration was observed, and mixtures containing 20% FGD gypsum failed to meet the M30 design requirement at 28 days. SEM–EDX confirmed that optimum sulfate activation produced a dense C–(A)–S–H-rich matrix, while excess sulfate caused matrix disruption. The findings establish 10% FGD gypsum by total binder mass as the optimum sulfate activation threshold for the investigated GGBFS and FGD gypsum sources at w/b = 0.45, and demonstrate the potential of untreated industrial FGD gypsum to produce durable, low-clinker structural concrete. Full article

The disposal of high-water-content bentonite slurry generated from underground construction presents prominent environmental and technical challenges, calling for low-carbon and efficient consolidation technologies. This study proposes an integrated flocculation–preloading–electro-osmosis (FPE) method using anionic polyacrylamide (APAM) combined with ground granulated blast furnace slag to strengthen dewatering and stabilization of bentonite slurry. Settlement column experiments were conducted to determine the optimal APAM dosages. A series of FPE consolidation experiments were performed to monitor drainage, settlement, electrical current, temperature and post-treatment soil properties, combined with microstructural analysis to reveal the synergistic mechanism. The results show that APAM creates abundant seepage channels via adsorption bridging and flocculation, significantly accelerating early-stage drainage and settlement rates without obviously increasing total drainage and final settlement. The polymer hydrogel homogenizes soil structure, leading to a gradual increase in moisture content and decrease in shear strength from anode to cathode, and effectively eliminates cracking during electro-osmosis. The temporary seepage channels induce a faster initial current rise, while the polymer coating increases apparent resistivity after free water discharge, thereby reducing current and temperature during the electro-osmotic consolidation stage. Appropriate APAM dosage thickens the electric double layer to raise the free swell ratio, whereas excessive dosage restricts swelling by particle coating. Microscopic observations confirm that chain-structured APAM and flocculent C-(A)-S-H hydration products cement soil particles and fill pores, improving soil integrity and shear strength. Overall, APAM improves early-stage efficiency and soil uniformity/integrity. In addtion, its combined effect with slag on bentonite shear strength increase is relatively higher than that of 0% slag condition. The integrated FPE technique realizes synchronous high-efficiency dewatering and low-carbon stabilization of high-water-content bentonite slurry, providing a novel and practical solution for engineering slurry disposal. Full article

To support the achievement of the carbon peaking and carbon neutrality goals and promote the resource utilization of industrial solid waste, a ternary solid waste composite cementitious material was prepared by blending ground granulated blast-furnace slag (GGBFS), fly ash (FA), and carbide slag (CS) with cement. The optimal mix ratio was determined through single-factor experiments and response surface methodology. The synergistic hydration mechanism was elucidated using microstructural characterization techniques, including XRD, FTIR, TG-DTG, and SEM. The composite material was then applied to a semirigid base course, and its mechanical properties and durability were systematically evaluated. The results indicate that the optimal levels of FA, GGBFS, and CS investigated in the single-factor experiments are 20–40%, 30–50%, and 2–6%, respectively. The optimal mix ratio of the ternary solid waste composite is 21.0% FA, 36.3% GGBFS, and 5.7% CS. The underlying microstructural mechanism is that carbide slag creates a highly alkaline environment, which activates the pozzolanic activity of GGBFS and fly ash, leading to the formation of hydration products dominated by C-(A)-S-H gel. With increasing curing age, the gel structure evolves from a loose and disordered state to a dense and ordered state, ultimately forming a compact microstructure based on a highly polymerized C-(A)-S-H gel matrix. The 7-day unconfined compressive strength of the stabilized gravel using the solid waste-based composite cementitious material reached 5.93 MPa, and the 28-day drying shrinkage coefficient was reduced by 18.3% compared with that of cement-stabilized gravel. After 18 freeze–thaw cycles, the compressive strength increased by 2.4%, with the pore structure characterized by a “macropores decreasing, micropores increasing” refinement pattern. After 18 wetting–drying cycles, the cumulative strength loss was 11.26%, outperforming cement-stabilized gravel. Combined with SEM observations, these performance improvements are attributed to the densely intertwined hydration products, particularly C-S-H gel, which effectively fill the voids between aggregate particles and significantly enhance the volume stability, freeze–thaw resistance, and wetting–drying durability of the stabilized gravel. The application of this cementitious material in a semirigid base course demonstrates excellent mechanical and durability properties, providing a theoretical basis and technical support for the widespread application of industrial solid waste in road engineering. Full article

Dredged soil treatment and reuse remain major economic and environmental challenges in geotechnical and highway engineering. Cement-based stabilization can effectively improve the engineering properties of dredged soil, but its large-scale use is associated with high material costs, energy consumption, and carbon emissions. In this study, a solid-waste-based binder composed of calcium carbide slag (CS), ground granulated blast-furnace slag (GGBS), and fly ash (FA) was developed as a potential cement alternative for stabilizing organic-rich dredged soil in road applications. Based on mortar-performance screening, a CS:GGBS:FA mass ratio of 0.25:0.50:0.25 was selected, and the road performance and durability of the resulting CS-GGBS-FA (CGF)-stabilized soil were systematically evaluated. Laboratory tests, including California bearing ratio (CBR), dynamic resilient modulus (M_R), wet–dry (W–D) cycling, and freeze–thaw (F−T) cycling, were conducted, with cement-stabilized soil used as a reference. The results showed that the CBR and M_R of the CGF-stabilized soil increased significantly with binder content and curing time, meeting the requirements for subgrade and subbase applications under different highway classes. Compared with cement-stabilized soil, the CGF-stabilized soil showed slightly lower CBR and M_R values at the same binder content but exhibited favorable strength retention and mass stability during W–D and F–T cycling. Overall, a CGF content of at least 8% provided sufficient strength, stiffness, and durability for road use. Full article

Reusing industrial byproducts to prepare recycled aggregate concrete (RAC) is a sustainable approach that can protect the ecological environment. This study tested the possibility of preparing an eco-efficient recycled concrete containing steel slag (SS), ground-granulated blast-furnace slag (GGBS), and polypropylene (PP) fibers to avoid resource waste and depletion and decrease CO₂ emissions. To this end, 12 mix proportions were designed to analyze the effects of SS, GGBS, and PP fibers on the macro- and micro-performances of the developed RAC. The experimental results showed that increasing the SS content decreased the RAC mechanical strength, whereas partially substituting SS with GGBS in the RAC improved the mechanical properties, especially at a later stage. Adding PP fibers to the RAC containing SS and GGBS significantly increased the splitting tensile strength. However, it had little effect on the compressive strength as the PP fiber content was less than 0.6%. The microscopic experiment revealed that adding GGBS promoted the degree of hydration of SS, reduced the Ca (OH)₂ content, made the ITZ structure more compact, and optimized the pore characteristics of the RAC. Furthermore, according to the raw materials and results of mechanical properties, a hybrid Genetic Algorithm/Artificial Neural Network (GA-ANN) technique was proposed to predict the compressive strength of the RAC containing SS, GGBS, and PP fibers. We found that the proposed GA-ANN model effectively predicts the compressive strength. The findings of this study demonstrate that preparing RAC incorporating SS, GGBS, and PP fibers is promising for the reuse of industrial byproducts and construction waste. Full article

This study investigates the use of mussel shells (MSs), a biogenic by-product of the food industry, as a partial replacement for ground granulated blast furnace slag (GBFS) in alkali-activated mortars. Given their high CaCO₃ content, MSs represent a sustainable secondary raw material that reduces both waste disposal burden and reliance on natural resources, while offering a low-carbon alternative to conventional cement-based binders. Alkali-activated mussel shell/slag mortars (AAMSs) were produced with MS replacement ratios of 0%, 5%, 10%, 15%, and 20% by mass of GBFS. Sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) were used as alkaline activators. Fresh specimens were cured at 60 °C for 48 h. The experimental program included workability, compressive and flexural strength, water absorption, porosity, density, capillarity, ultrasonic pulse velocity (UPV), and freeze–thaw (F-T) resistance tests. Increasing MS content slightly reduced flowability and mechanical strength, while increasing water absorption, porosity, and capillarity. The M0 series achieved the highest 28-day compressive strength (54.06 MPa), while M15 exhibited the highest flexural strength (5.23 MPa). Following F-T cycling, the 5% and 10% MS series demonstrated the best compressive strength (30 MPa). The 10% MS exhibits a relatively balanced overall performance, providing the best balance between mechanical performance, F-T resistance, and microstructural stability, as confirmed by scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDS) analyses showing elevated Ca/Si ratios and the formation of Ca-rich crystalline phases. Full article