Search Results (193)

This study investigates the effectiveness of geopolymer-based binders for the stabilization of silty sand, aiming to improve its strength and durability under cyclic environmental conditions. A composite binder consisting of Ground Granulated Blast-furnace Slag (GGBS) and Recycled Glass Powder (RGP), modified with nano poly aluminum silicate (PAS), was used to treat the soil. The long-term performance of the stabilized soil was evaluated under cyclic wetting–drying (W–D) conditions. The influence of PAS content on the mechanical strength, environmental safety, and durability of the stabilized soil was assessed through a series of laboratory tests. Key parameters, including unconfined compressive strength (UCS), mass retention, pH variation, ion leaching, and microstructural development, were analyzed using field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS). Results revealed that GGBS-stabilized specimens maintained over 90% of their original strength and mass after eight W–D cycles, indicating excellent durability. In contrast, RGP-stabilized samples exhibited early strength degradation, with up to an 80% reduction in UCS and 10% mass loss. Environmental evaluations confirmed that leachate concentrations remained within acceptable toxicity limits. Microstructural analysis further highlighted the critical role of PAS in enhancing the chemical stability and long-term performance of the stabilized soil matrix. Full article

Ground granulated blast-furnace slag (GGBS), a waste product generated during steel production, can be added as a substitute for cement in concrete to mitigate the environmental impact of the cement and steel industries. However, the use of GGBS is limited because it decreases the early strength development of cement or concrete. This study evaluated the performance of incorporating synthesized C-S-H nanoparticles to enhance the compressive strength, early hydration, and microstructure of cement composite. The synthesized C-S-H nanoparticles were produced at standard atmospheric pressure and room temperature. Heat of hydration, X-ray diffraction, and thermogravimetric analyses were conducted to investigate the hydration and mechanical properties of the cement containing the C-S-H nanoparticles. Further, mercury intrusion porosimetry was conducted to examine the pore structures. The experimental finding demonstrated that adding C-S-H nanoparticles accelerated the early hydration progress in the cement composites, thereby increasing their initial compressive strength. Full article

The utilization of steel slag (SS) in construction materials represents an effective approach to improving its overall recycling efficiency. This study incorporates SS into a conventional ground granulated blast-furnace slag (GGBS)–fly ash (FA)-based binder system to develop a ternary system comprising SS, GGBS, and FA, and investigates how this system influences the static mechanical properties of ultra-high-performance geopolymer concrete (UHPGC). An axial point augmented simplex centroid design method was employed to systematically explore the influence and underlying mechanisms of different binder ratios on the workability, axial compressive strength, and flexural performance of UHPGC, and to determine the optimal compositional range. The results indicate that steel slag has a certain negative effect on the flowability of UHPGC paste; however, with an appropriate proportion of composite binder materials, the mixture can still exhibit satisfactory flowability. The compressive performance of UHPGC is primarily governed by the proportion of GGBS in the ternary binder system; an appropriate GGBS content can provide enhanced compressive strength and elastic modulus. UHPGC exhibits ductile behavior under flexural loading; however, replacing GGBS with SS significantly reduces its flexural strength and energy absorption capacity. The optimal static mechanical performance is achieved when the mass proportions of SS, GGBS, and FA are within the ranges of 9.3–13.8%, 66.2–70.7%, and 20.0–22.9%, respectively. This study provides a scientific approach for the valorization of SS through construction material applications and offers a theoretical and data-driven basis for the mix design of ultra-high-performance building materials derived from industrial solid wastes. Full article

This study focuses on the development of high-performance composite cementitious materials for offshore engineering applications, addressing the critical challenges of durability, environmental degradation, and carbon emissions. By incorporating polycarboxylate superplasticizers (PCE) and combining fly ash (FA), ground granulated blast furnace slag (GGBS), and silica fume (SF) in various proportions, composite mortars were designed and evaluated. A series of laboratory tests were conducted to assess workability, mechanical properties, volume stability, and durability under simulated marine conditions. The results demonstrate that the optimized composite exhibits superior performance in terms of strength development, shrinkage control, and resistance to chloride penetration and freeze–thaw cycles. Microstructural analysis further reveals that the enhanced performance is attributed to the formation of additional calcium silicate hydrate (C–S–H) gel and a denser internal matrix resulting from secondary hydration. These findings suggest that the proposed material holds significant potential for enhancing the long-term durability and sustainability of marine infrastructure. Full article

To address the challenges of concrete construction in polar regions, this study investigates the feasibility of fabricating cement-based materials under severely low temperatures using electric-induced heating curing methods. Cement mortars incorporating fly ash (FA-CM), ground granulated blast furnace slag (GGBS-CM), and metakaolin (MK-CM) were cured at environmental temperatures of −20 °C, −40 °C, and −60 °C. The optimal carbon fiber (CF) contents were determined using the initial electric resistivity to ensure a consistent electric-induced heating curing process. The thermal profiles during curing were monitored, and mechanical strength development was systematically evaluated. Hydration characteristics were elucidated through thermogravimetric analysis (TG), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) to identify phase compositions and reaction products. Results demonstrate that electric-induced heating effectively mitigates the adverse effect caused by the ultra-low temperature constraints, with distinct differences in the strength performance and hydration kinetics among supplementary cementitious materials. MK-CM exhibited superior early strength development with strength increasing rates above 10% compared to the Ref. specimen, which was attributed to the accelerated pozzolanic reactions. Microstructural analyses further verified the macroscopic strength test results that showed that electric-induced heating curing can effectively promote the performance development even under severely cold environments with a higher hydration degree and refined micro-pore structure. This work proposes a viable strategy for polar construction applications. Full article

Facing sand and gravel shortages, construction waste accumulation, and the “double carbon” goals, improving the performance of recycled aggregate concrete (RAC) and utilizing mineral waste slag are key to the development of green, low-carbon building materials. To enhance the mechanical performance of RAC and facilitate the sustainable utilization of mineral waste, this study innovatively incorporated copper slag (CS), ground granulated blast furnace slag (GGBS), and basalt fiber (BF) into RAC. The modified RAC’s compressive, split tensile, and flexural strengths were systematically investigated. Experimental results indicated that incorporating appropriate amounts of CS or GGBS as single admixtures could effectively enhance the mechanical properties of RAC, with 20% (w) GGBS showing the most pronounced improvement. Compared with RAC, its 28 d compressive strength, split tensile strength and flexural strength were improved by 21.3%, 9.7% and 8.1%, respectively. As opposed to single admixture, 10% CS + 10% GGBS admixture can further improve the mechanical properties of recycled concrete. Compared with RAC, its 28 d compressive strength, split tensile strength, and flexural strength were improved by 25.6%, 29.7%, and 16.6%. The study also showed that 0.2% BF admixed on top of 10% CS + 10% GGBS could still significantly improve the mechanical properties of recycled concrete, and its 28 d compressive strength, split tensile strength, and flexural strength were improved by 31.3%, 35.9%, and 31.2%, compared with RAC, respectively. By XRF, SEM, and EDS techniques, the underlying mechanisms governing the mechanical behavior of RAC were elucidated from the microscale perspective of basalt fiber and industrial waste residues. These findings provide a solid theoretical foundation and a viable technical pathway for the widespread application of recycled aggregate concrete in civil engineering projects. Full article

Geopolymer concrete is a promising construction material that acts as an alternative to cement concrete. Unlike traditional cement concrete, geopolymers are environmentally friendly materials, the production of which does not involve significant carbon dioxide emissions. However, the structure formation and properties of geopolymers significantly depend on raw materials and are insufficiently studied. The aim of the study is to select the optimal combination of ground granulated blast furnace slag (GGBS) and fly ash (FA) as a binder and the optimal content of polypropylene fiber to create a sustainable, environmentally friendly and effective geopolymer concrete. To study various compositions of geopolymer binders selected by combining GGBS and FA, experimental geopolymer concrete mixtures and samples from them were manufactured. The density and slump of fresh concrete and the density and compressive strength of hardened composites were studied as mechanical characteristics. The microstructure of the geopolymer matrix was analyzed using optical and scanning electron microscopes. The most rational combination of GGBS 80% and FA 20% was determined, which allows obtaining a composite with the highest compressive strength of up to 31.5 MPa. A dispersion reinforcement study revealed that 0.8% polypropylene fiber (PF) is optimal. This allowed us to increase the compressive strength by 7.3% and the flexural strength by 48.7%. The geopolymer fiber concrete obtained in this study is a sustainable and environmentally friendly alternative composite material and has sufficient performance properties for its use as an alternative to cement concrete. Full article

The use of recycled glass powder (RCGP) is investigated as a partial replacement for ground granulated blast furnace slag in blended CEM II/A-LL cements using thermodynamic modelling to simulate cement paste hydration at a water-to-cement (w/c) ratio of 0.5. This study allows a rapid means of examining the likely evolution of these materials over the first two to three years, allowing experimental work to focus on promising formulations. A comparison is made between the evolving solid phase and solution chemistries of four materials: a standard Portland-limestone (CEM II/A-LL), a ‘control’ blend, comprising equal quantities of CEM II/A-LL with GGBS and two novel blended cements containing RCGP. These represent 15% replacement (by mass) of GGBS by RCGP blended with either 40% or 60% CEM II/A-LL. The simulations were performed using the code HYDCEM, a cement hydration simulator, which calls on the thermodynamic model PHREEQC to sequentially simulate the evolution of the four cements. The results suggest that partial replacement of GGBS by 15% RCGP results in no significant change in system chemistry. The partial replacement of cementitious slag by waste container glass provides a route by which this material can be diverted from the landfill inventory, and the mass-balance and energy balance implications will be reported elsewhere. Full article

This study explores the potential of calcium carbide residue (CCR) as an alternative activator for ground granulated blast-furnace slag (GGBS) to reduce reliance on ordinary Portland cement (OPC) in mortar production. A series of OPC-GGBS-CCR ternary binders were prepared and evaluated for their fresh and mechanical properties over various curing periods. The findings showed that mortars’ fresh and mechanical characteristics were significantly improved with longer curing times, suggesting CCR’s potential to efficiently activate GGBS, thereby benefiting the environment and economy. Significant enhancements in compressive strengths were observed after 7 days of curing, with increases of 44%, and 69–144% for OPC and OPC-GGBS-CCR ternary binders, respectively, while the utilization of activated binders led to flexural strength growth compared to three days of curing, with improvements of 70–173% for OPC-GGBS-CCR ternary binders, respectively. Microstructural analyses confirmed accelerated hydration and increased product formation due to CCR’s calcium content. An optimal mix ratio of OPC:GGBS:CCR = 1:1:0.5 demonstrated mechanical properties comparable to OPC mortars after 28 days, highlighting CCR’s potential for sustainable cementitious materials. Full article

Frequently, the viscous mixture from shield operations is disposed of because its significant water ratio and the presence of polymers like foaming agents result in subpar structural qualities, contributing to the unnecessary consumption of land and the squandering of soil assets. Therefore, these problems urgently need to be solved economically and effectively. This study relies on the shield sludge produced by Qingdao Metro Line 6 project, and sand and shield sludge were used as the raw materials for synchronous grouting. By applying the basic principles of geopolymerization, ingredients like shield sludge and ground granulated blast furnace slag (GGBS) were mixed with sodium hydroxide, serving as the activating agent, in the preparation of the simultaneous grout formulas. A broad range of laboratory tests was conducted to evaluate the performance of these grout formulations. The effects of varying material ratios on key performance indicators—namely, fluidity, water secretion rate, setting time, and 3-day unconfined compressive strength (UCS)—were systematically analyzed. Based on these findings, the optimal material ratios for shield sludge-based synchronous grouting materials were proposed. Subsequently, component geopolymer was prepared from the activated shield sludge and shield sludge without adding any additional alkaline activators by simply adding water. A geopolymer with a 28-day compressive strength of 51.08 MPa was obtained when the shield sludge dosing was 60 wt%. This study aims to provide a reference for the preparation of synchronous grouting materials for the resource utilization of shield sludge. Full article

To investigate the sulfate resistance of recycled concrete with composite admixtures under dry–wet cycling, a single-factor experimental design was first conducted to study the deterioration patterns of recycled concrete with single and composite admixtures (ground granulated blast furnace slag (GGBS) and fly ash) under sulfate attack. Based on the single-factor test results, orthogonal experiments were designed with composite admixtures as one influencing factor. Quantitative analysis was performed to determine the impact magnitude and significance of various factors on the sulfate resistance of recycled concrete at different corrosion ages. A damage model for recycled concrete under sulfate dry–wet cycling was established for preliminary service life prediction. The experimental results indicated that the sulfate resistance performance followed the sequence of composite admixtures > single slag admixture > single fly ash admixture. When uncycled (0 cycles), the influence ranking of factors was B (water–binder ratio) > A (recycled coarse aggregate replacement rate) > C (GGBS + fly ash content). After 60 and 120 cycles, the ranking became B > C > A. For the compressive strength regression model, the measured values deviated significantly from the calculated values (−6.88% to 16.66%), while the dynamic elastic modulus model showed good agreement between the measured and calculated values (−2.86% to 4.87%). A three-indicator lifespan prediction equation was established. Using practical engineering parameters (30% recycled aggregate replacement, 0.4 water–binder ratio, 20% fly ash and 20% slag content), the predicted service life of this recycled concrete project was T = 117 years. Therefore, incorporating fly ash and slag can effectively improve weak zones in recycled concrete and enhance its durability. Full article

This study, from the perspective of resource utilization and carbon sequestration, developed a novel lightweight carbonated solidified slurry material using reactive magnesium oxide (MgO), ground granulated blast furnace slag (GGBS), and carbide slag as stabilizers, with carbonation induced by a CO₂ foaming method. The physical and mechanical properties of the material were investigated. Based on the optimal mix proportion, the effects of MgO content, CO₂ foam dosage, and stabilizer dosage on wet density, flowability, moisture content, and unconfined compressive strength were analyzed. The results indicate that wet density increases with increasing MgO and stabilizer content but decreases with increasing CO₂ foam dosage. Flowability decreases with increasing MgO and stabilizer content but improves with a higher CO₂ foam dosage. Unconfined compressive strength increases with curing age and stabilizer content but decreases with increasing CO₂ foam dosage. Additionally, prolonged curing enhances both moisture content and unconfined compressive strength. These findings provide a theoretical basis for engineering applications. Full article

Considering the urgent need for sustainable construction materials, this study investigates the mechanical and microstructural responses of novel hybrid geopolymer concrete blends incorporating Fly Ash (FA), Ground Granulated Blast Furnace Slag (GGBS), Cement (C) and Precipitated Silica (PS) as partial replacements for traditional cementitious materials. The motive lies in reducing CO₂ emissions associated with Ordinary Portland Cement (OPC). The main aim of the study was to optimise the proportions of industrial wastes for enhanced performance and sustainability. The geopolymer mixes were activated using a 10 M sodium hydroxide (NaOH)—Sodium Silicate (Na₂SiO₃) solution and cast into cubes (100 mm), cylinders (100 mm × 200 mm) and prism specimens for compressive, split tensile and flexural strength testing, respectively. Six combinations of mixes were studied: FA/C (50:50), GGBS/C (50:50), FA/C/PS (50:40:10), FA/GGBS/PS (50:40:10), GGBS/C (50:50) and GGBS/FA/PS (50:40:10). The results indicated that the blend with 50% FA, 40% GGBS and 10% PS exhibited higher strength. Mixes with GGBS and PS presented a l0 lower slump due to rapid setting and higher water demand, while GGBS-FA-cement mixes indicated better workability. GGBS/C exhibited a 24.6% rise in compressive strength for 7 days, whereas FA/C presented a 31.3% rise at 90 days. GGBS/FA mix indicated a 35.5% strength drop from 28 days to 90 days. SEM and EDS analyses showed that FA-rich mixes had porous microstructures, while GGBS-based mixes formed denser matrices with increased calcium content. Full article

High-water content dredged sludge from waterways, with potential for sustainable use as high-performance fillers, was effectively treated using the vacuum preloading-flocculation-solidification combined method (denoted as the VP-FSCM). This study investigated the effect of flocculant and curing agent dosages on the solidification of sludge with initially poor mechanical properties. Ground granulated blast-furnace slag (GGBS) and ordinary Portland cement (OPC) were selected as composite curing agents, while anionic polyacrylamide (APAM) and slaked lime were used as a mixed flocculant. Laboratory experiments were conducted to examine the effects of different dosages of curing agents and flocculants on deposition dehydration, strength characteristics, water content after curing, as well as the spatial distribution of them under the combined method. Additionally, the conventional sludge solidified method treated by GGBS and OPC (denoted as the GCSM) was also investigated and compared. The results indicate that increasing the dosage of curing agent from 4.5% to 10.5% enhances the shear strength of samples treated with VP-FSCM by up to 3–5 times compared to those treated with GCSM. The optimal ratio for the composite curing agent is GGBS/OPC = 1, with optimum dosages for the composite flocculant composed of APAM at 0.125% and slaked lime at 1.5%. When admixture dosage is optimal, it allows for better utilization of the advantages from coupling effects such as flocculation dehydration, vacuum preloading, and chemical curing, thereby significantly improving mechanical properties of the sludge. Full article

Awareness of environmental sustainability is driving the shift from conventional Portland cement, a major contributor to carbon dioxide emissions, to more sustainable alternatives. This study focuses on developing a geopolymer concrete by optimizing geopolymer concrete mixtures with various ratios of Ground Granulated Blast Furnace Slag (GGBS) and pulverized fly ash (PFA) as precursors, aiming to find a mix that maximizes strength while minimizing environmental impacts. The precursor was activated using a laboratory-synthesized silica fume (SF)-derived sodium silicate solution in combination with NaOH at a molarity of 10M. This study aims to find the optimal geopolymer concrete mix with a 0.55 water-to-binder ratio, a 0.40 alkali-to-precursor ratio, and a 1:1 sodium silicate to sodium hydroxide ratio. Ordinary Portland cement was used as the control mix binder (C), while the geopolymer mixes included varying GGBS-PFA compositions [CL0 (50% GGBS—50% PFA), CL1 (60% GGBS—40% PFA), CL2 (70% GGBS—30% PFA), CL3 (80% GGBS—20% PFA), and CL4 (90% GGBS—10% PFA)]. The engineering performance of the mixtures was assessed using slump, unconfined compressive strength, split tensile, and flexural strength tests in accordance with their relevant standards. Observations showed that GPC specimens exhibited similar or slightly higher strength values than conventional concrete using PC. In addition to strength, geopolymers have a smaller environmental footprint, consuming less energy and reducing greenhouse gas emissions. These qualities make geopolymer concrete a sustainable construction option that aligns with global efforts to reduce carbon emissions and conserve resources. Full article