Search Results (214)

This study evaluates the mechanical properties and carbonation resistance of alkali-activated mortars (AAMs) formulated with ground granulated blast-furnace slag (GGBS) and recycled construction spoil (CS). The experimental variables included the water-to-solid ratio, alkali content, activator type (NaOH vs. Na₂SiO₃), and GGBS/CS mass ratio. The effects of these parameters on workability, flexural strength, and compressive strength were analyzed, along with the influence of accelerated carbonation curing. Results indicate that CS incorporation reduces flowability, with NaOH-activated mortars displaying marginally better workability than the Na₂SiO₃-activated counterparts. At an alkali content of 6.5% and a water-to-solid ratio of 0.45–0.5, a 30% CS replacement significantly improved the 7-day flexural strength in Na₂SiO₃-activated systems. Compressive strength generally increased with higher alkali content, though this effect diminished at elevated CS substitution levels. Under supercritical carbonation, NaOH-activated GGBS exhibited a ~20% strength increase, whereas Na₂SiO₃-activated GGBS showed negligible change or a slight reduction. Blends containing 50% CS demonstrated minimal carbonation-induced alterations. These findings provide insights into optimizing industrial byproduct utilization in AAMs while improving their carbonation durability, supporting sustainable construction material development. Full article

The disposal of industrial waste poses a significant environmental challenge, often leading to pollution and degradation of surrounding and terrestrial ecosystems. This study investigates the sustainable valorization of such wastes through the development of one-part geopolymer mortars. Solid sodium silicate was employed as a dry alkali activator for binary blends comprising ground granulated blast-furnace slag (GGBS), clay brick powder (CBP), steel slag (SS), and fly ash (FA), with all mixtures cured under ambient conditions. The mortars were evaluated in terms of fresh properties (flow and setting time) and hardened characteristics, including compressive strength, density, water absorption, and porosity. Durability performance was assessed through mass loss, visual degradation, and compressive strength retention following exposure to acidic (H₂SO₄, HCl) and sulfate environments. Microstructural characterization using XRD, SEM, and FTIR provided insight into the mechanisms of gel formation and degradation in aggressive media. The results revealed that incorporating 5% FA into GGBS-based mortars enhanced 28-day compressive strength by 21.7% compared with the control mix. The inclusion of industrial by-products promoted the formation of C–S–H and C–(A)–S–H gels, contributing to a denser and more refined microstructure. Overall, the findings demonstrate that one-part geopolymer mortars offer a promising, eco-efficient, and durable alternative to traditional cementitious systems, while also addressing safety and handling concerns associated with liquid alkaline activators used in conventional two-part geopolymer formulations. Full article

The development of sustainable self-compacting concrete (SCC) requires alternative binders that minimise ordinary Portland cement (OPC) consumption while ensuring long-term performance. This study investigates sulfate-activated SCC (SA SCC) incorporating high volumes of industrial by-products, whereby 72% ground granulated blast furnace slag (GGBS) and 18% fly ash (FA) were activated with varying proportions of OPC and gypsum. Quarry dust was used as a fine aggregate, while granite and electric arc furnace (EAF) slag served as coarse aggregates. Among all formulations, the binder containing 72% GGBS, 18% FA, 4% OPC, and 6% gypsum was identified as the optimum composition, providing superior mechanical performance across all curing durations. This mix achieved slump flow within the EFNARC SF2 class (700–725 mm), compressive strength exceeding 50 MPa at 270 days, and flexural strength up to 20% higher than OPC SCC. Drying shrinkage values remained below Eurocode 2 and ASTM C157 limits, while EAF slag increased density, but slightly worsened shrinkage compared to granite mixes. Microstructural analysis (SEM-EDX) confirmed that strength development was governed by discrete C-S-H and C-A-S-H gels surrounding unreacted binder particles, forming a dense interlocked matrix. The results demonstrate that sulfate activation with a 4% OPC + 6% gypsum blend enables the production of high-performance SCC with 94–98% industrial by-products, reducing OPC dependency and environmental impact. This work offers a practical pathway for low-carbon SCC. Full article

It is well known that elevated phosphate concentrations in water bodies trigger the eutrophication process, posing adverse environmental, health, and economic consequences that necessitate effective removal solutions. Phosphate removal has therefore been widely studied using various methods, including chemical precipitation, membrane filtration, and crystallisation. However, most of these methods are often expensive or inefficient for low phosphate concentrations. Therefore, in this study, an eco-friendly, sustainable and biodegradable adsorbent was manufactured by extracting calcium ions from an industrial by-product, ground granulated blast furnace slag (GGBS) and magnesium ions from magnesium dross (MgD), then immobilising them on sodium alginate to form Ca-Mg-SA beads. The new adsorbent was applied to remove phosphate from water under different flow patterns (batch and continuous flow), initial pH levels, contact times, agitation speeds and adsorbent doses. Additionally, the degradation time of the new adsorbent, recycling potential, its morphology, formation of functional groups and chemical composition were investigated. The results obtained from batch experiments demonstrated that the new adsorbent achieved 90.2% phosphate removal efficiency from a 10 mg/L initial concentration, with a maximum adsorption capacity of 1.75 mg P/g at an initial pH of 7, a contact time of 120 min, an agitation speed of 200 rpm and an adsorbent dose of 1.25 g/50 mL. The column experiments demonstrated a 0.82 mg P/g removal capacity under the same optimal conditions as the batch experiments. The findings also showed that the adsorption process fitted well to the Freundlich and Langmuir isotherm models and followed a pseudo-second-order kinetic model. Characterisation of Ca-Mg-SA beads using EDX, SEM and FTIR confirmed successful ion immobilisation and phosphate adsorption. Furthermore, the beads fully biodegraded in soil within 75 days and demonstrated potential recycling as a fertiliser. Full article

Ground granulated blast-furnace slag (GGBS) is a typical supplementary cementitious material that can delay the early hydration of cement. In this study, a novel integrated sensor was employed to continuously monitor the hydration process of cementitious materials and to characterize the influence of GGBS addition on hydration behavior. The monitoring results show that the signal parameters, including amplitude, energy, and frequency domain, varied significantly during hydration. For plain cement paste (0% GGBS), the maximum signal amplitude after 24 h decreased by 28.2% compared with that at 0 h. As the GGBS content increased to 5%, 10%, 20%, 30%, 40%, and 50%, the amplitude reduction ratios increased to 34.1%, 38.1%, 36.8%, 53.1%, 47.4%, and 59.0%, respectively. A similar trend was observed for the signal energy, with corresponding decreases of 34.3%, 41.5%, 39.3%, 44.5%, 53.1%, 47.0%, and 59.5%. These results clearly indicate that the incorporation of GGBS delays the early hydration of cement and suppresses the evolution of ultrasonic response. Short-time Fourier transform analysis further confirmed that the main frequency peak shifted toward a later time with increasing GGBS content, demonstrating the retarding effect of slag on hydration kinetics. This study verifies the feasibility of using integrated sensors for in situ monitoring of the hydration delay process in GGBS-blended cementitious materials. Full article

The large-scale accumulation of high-sulfur lead–zinc tailings poses serious environmental and safety challenges, while the increasing shortage of traditional mineral admixtures such as fly ash and slag highlights the urgent need for sustainable alternatives. This study aims to develop a high-performance mineral admixture using lead–zinc tailings characterized by high SO₃ content and low pozzolanic activity. The effects of four activation routes—mechanical grinding, wet magnetic separation, wet magnetic separation–mechanical grinding, and mechanical grinding–high-reactivity mineral admixture synergistic modification—were systematically compared in terms of tailings fineness, SO₃ reduction, and activity index. The results indicate that single mechanical grinding can achieve the fineness requirement of Grade II admixtures specified in GB/T 1596–2017 (45 μm residue ≤ 30%), but the 28-day strength activity index only reached 58.64%, and the SO₃ content remained above the standard limit. Wet magnetic separation effectively reduced the SO₃ content to below 3.5%, and the combined process yielded a product with an activity index of up to 74.51%. Further improvement was achieved through a “mechanical grinding–high-reactivity mineral admixture synergistic modification” process, incorporating fly ash (FA), ground granulated blast furnace slag (GGBS), and silica fume (SF). Among these, SF exhibited the most pronounced synergistic effect. The optimal mixture, composed of 85.19% ground tailings and 14.81% SF, achieved the highest 28-day activity index of 76.35%. This process enables full utilization of tailings while maintaining a simplified flow, lower energy consumption, and superior product performance. The findings provide a feasible and efficient technological route for the high-value utilization of high-sulfur tailings and contribute to promoting green mining and sustainable resource development. Full article

Recycled aggregate sourced from construction and demolition waste presents a viable means of reducing the environmental impact associated with concrete production. However, previous research has shown that concrete incorporating recycled aggregate typically exhibits reduced strength and increased susceptibility to deterioration. In this work, eight concrete mixes were prepared using both virgin and locally sourced recycled coarse aggregate from the United Arab Emirates, with selected mixes incorporating various combinations of supplementary cementitious materials (SCMs) (ground granulated blast-furnace slag (GGBS) and silica fume). The mixes were tested over a period of 180 days to evaluate key mechanical properties, durability, and embodied carbon. It was found that partial replacement of Portland cement with GGBS and silica fume had no marked beneficial effect on the strength and water absorption of recycled aggregate concrete when compared to mixes containing virgin aggregate. However, improvements in resistance to chloride ingress and reductions in drying shrinkage were observed. Notably, the incorporation of SCMs resulted in a significant reduction in embodied carbon, with reductions in excess of 40% when compared with conventional Portland cement concrete. Full article

Composite geopolymer concrete (CGPC), is receiving growing attention in the construction sector for its sustainable nature, environmental benefits, and its valuable role in promoting efficient waste utilization. The strategic incorporation of reinforcing fibers into geopolymer concrete (GPC) matrices is critical for enhancing mechanical performance and meeting the durability requirements of high-performance construction applications. Although substantial research has focused on strength enhancement of fiber-reinforced geopolymer concrete (FGPC) individually, it has neglected practical considerations such as energy use for curing and life-cycle assessments. Thus, this study investigates the cost-effective aspects of FGPC cured under different regimes. Different cementitious binders were incorporated, i.e., fly ash (FA) and ground granulated blast-furnace slag (GGBS), in addition to alkaline activators (a combination of sodium hydroxide and sodium silicate), hooked-end steel fibers (HESFs), basalt fibers (BFs), and polypropylene fibers (PPFs), as well as aggregates (gravel and sand). The effect of different geopolymer-based materials, reinforcing fibers, and different curing regimes on the mechanical, durability, and economic performance were analyzed. Results showed that the applied thermal curing regimes (oven curing or steam curing) had a considerable impact on durability performance, compressive strength, and flexural strength development, especially for GPC mixes involving high FA content. Cost analysis outcomes suggested that the most affordable option is GPCM1 (100% FA without fibers), but it demonstrates low strength under ambient curing conditions; RGCM4 (100% GGBS and 0.75% HESF) provided the best strength and durability option but at higher material cost; RGCM7 (50% FA, 50% GGBS, and 0.75% HSF) exhibited a balanced choice since it offer satisfied strength and durability performance with moderate cost compared to other options. Full article

This experiment investigated the mechanical performance and acid resistance (when subjected to 28 days of exposure to sulfuric and nitric acid of five percent) of ambient-cured geopolymer concrete. Geopolymer concrete (GPC)—which is produced by using industrial by-products, including fly ash and ground granulated blast furnace slag (GGBS)—is a low-carbon and strong substitute of Ordinary Portland Cement (OPC). This experiment examines the mechanical and acid-resisting properties of ambient GPC with different GGBS (10, 30, and 50 percent) contents. The compressive, tensile, and flexural strengths were measured at 7, 14, and 28 days, and durability was measured under an exposure of 5% sulfuric and nitric acids. X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed that gypsum and ettringite were formed by sulfuric acid that weakened the structure, whereas surface decalcification was mostly caused by nitric acid. Mixes with a high fly ash content had more amorphous structures and better acid resistance, whereas those having high GGBS contents had high early strength because of high densities of the C–A–S–H gel. The findings indicate a strength–durability trade-off, which can be used to control the optimized mix design to produce sustainable and long-term infrastructure. Full article

In this work, the synergistic effects of mineral admixtures and advanced mixing processes are systematically accounted for steel fibre-reinforced recycled aggregate concrete (SFR-RAC). It studies the improvement of performance optimization in SFR-RAC, inherently weak ITZ by adding 0.5% hooked steel fibres and replacing cement with ground granulated blast furnace slag (25–50%), fly ash (20–40%) and silica fume (7–14%). The efficiency of double-mixing (DM) and triple-mixing (TM) procedures were comprehensively evaluated. Results showed that mineral admixtures could improve mortar-aggregate interface bond, and the triple-mix technique contributed to such improvement. The maximum performance was observed for the combination of 7%SF with triple mixing (7%SF-TM), which presented increased compressive, tensile and flexural strengths by 7–18%, 12–29%, and 16–31% respectively. The durability was significantly improved, and the water resistance could increase by 53% with addition of 7%SF-TM, chloride penetration depth reduced by 86% when incorporated with 25%GGBS-TM, acid attack decreased by 84% with addition of 14%SF-TM. Microstructural analysis (SEM, XRD) confirmed that these enhancements stem from a denser matrix and refined ITZ due to increased C–S–H formation. This study confirms that the strategic integration of fibre reinforcement, pozzolanic admixtures and optimized mixing protocols presents a viable pathway for producing sustainable concrete from construction waste. Full article

Phosphogypsum (PG) and Carbide Slag (CS) are two industrial byproducts that can be used as cementitious materials, and their synergistic effect provides excellent activation of ground granulated blast furnace slag (GGBS), which is traditionally activated by lime (LM). However, the behavior of PG-GGBS-CS ternary blended cement remains largely unexplored. In this study, the mechanical performance, hydration mechanisms, and environmental profile of PG–GGBS–CS binders in comparison with PG–GGBS–LM were evaluated by unconfined compressive strength (UCS), XRD, SEM, and TGA analyses. The optimum formulation containing 30% PG achieved 24.88 ± 1.24 MPa at 28 d, statistically comparable to 25.6 ± 1.28 MPa for PG–GGBS–LM. The synergistic activation of PG and CS/LM on GGBS has been identified as a crucial factor in the strengthening of UCS in ternary blended cement. Hydration products consisted mainly of calcium silicate hydrate (C–S–H) gels and Ettringite (AFt). Importantly, the CO₂ footprint of PG–GGBS–CS was reduced by 3.2% compared to that of PG–GGBS–LM. These findings establish CS as an effective substitute for lime in eco-binders, combining technical efficiency with carbon mitigation and offering a viable pathway for large-scale valorization of hazardous industrial residues. Full article

This study investigates the fact that reinforcing geopolymers with natural fibers provides a practical way to improve their strength and durability. Offering environmental benefits compared to Portland cement, their mechanical performance still presents challenges. The particularity of this study lies in the pretreatment of natural fibers to limit their degradation within the alkaline geopolymer matrix. It also explores the effect of their length and content on matrix geopolymer. XRD (X-ray diffraction) analysis confirmed the crystalline structure of the geopolymer gels, unaffected by fiber inclusion. SEM (Scanning Electron Microscopy) observations showed a decrease or even disappearance of mineralization in treated sisal and palm fibers within the matrix, along with some partial detachment of the fibers. Optimal compressive strength was achieved using metakaolin and GGBS (Ground Granulated Blast-furnace slag). Incorporating 4% short palm fibers enhanced flexural strength, while long sisal fibers led to a 30% increase in flexural strength compared to short fibers, representing a 10.7% overall improvement. However, current geopolymer systems still face challenges such as low flexural strength and brittleness, which this study overcomes by incorporating processed natural fibers as sustainable reinforcements with optimal content. Full article

This study demonstrates that synergistic pyrolysis and water-soaking pretreatment transforms municipal solid waste incineration fly ash (MSWI FA) into high-performance alkali-activated materials when combined with ground granulated blast furnace slag (GGBS). Pyrolysis reduced chlorine content by 94.3% and increased reactive components by 44.4%, thereby shifting hydration products from Friedel’s salt to ettringite (AFt). Subsequent water-soaking eliminated expansion-causing elemental aluminum, liberating activators for enhanced reaction completeness (29% higher cumulative heat release) and enabling a denser matrix with 71.5% harmless pores (<20 nm). The dual-treated FA (T-PFA) achieved exceptional mechanical performance—295.6% higher 56-day compressive strength versus untreated FA at a 1:1 ratio—while reducing porosity by 29.1% relative to pyrolyzed-only FA. Despite 22–38% increased total heavy metal content post-pyrolysis, matrix densification and enhanced C-A-S-H/AFt formation reduced Cr/Cd/Cu/Pb leaching by 11.3–66.7% through strengthened physical encapsulation and chemisorption, with all leachates meeting stringent HJ 1134-2020 thresholds. This integrated approach provides an efficient, environmentally compliant pathway for MSWI FA valorization in low-carbon construction materials. Full article

A novel thermal conductivity prediction model was developed to address the complex influence of pore structure in porous materials. This model incorporates pore size (d) and a pore distribution parameter (t) to calculate the material’s thermal conductivity. To validate the model’s accuracy, geopolymer foamed concrete (GFC) samples with varying pore structures were fabricated. These utilized ground granulated blast furnace slag (GGBS) as the precursor, a mixed solution of sodium hydroxide (NaOH) and sodium silicate as the alkaline activator, and sodium stearate (NaSt), hydroxypropyl methylcellulose (HPMC), and sodium carboxymethyl cellulose (CMC-Na) as foam stabilizers. Conventional pore size characterization techniques exhibit limitations; consequently, this research implements a high-fidelity machine vision-driven image analysis methodology. Pore size measurement is achieved through a combined technical approach involving equivalent diameter modeling and morphological optimization. The feasibility of the proposed theory is validated by our experimental data and data from previous literature, with the error between experimental and theoretical values maintained within 5%. The value of t increases with increasing porosity and increasing disorder in pore distribution. Based on the experimental data obtained in this study and the research data from previous scholars’ studies, the t value for porous materials can be categorized according to porosity: when porosity is approximately 30%, t ≈ 0.9; when porosity is 55~65%, t ranges from 1.2 to 1.3; and when porosity is approximately 80%, t ranges from 1.9 to 2.2. Full article

Three-dimensional concrete printing (3DCP) is rapidly emerging as a transformative construction technology, enabling formwork-free fabrication, geometric flexibility, and reduced labour. However, the lack of conventional reinforcement and the strict requirements for fresh and hardened properties present significant challenges. Fibre reinforcement and supplementary cementitious materials (SCMs), such as ground granulated blast furnace slag (GGBS), offer pathways to enhance printability while mitigating environmental impact. This study investigates the combined effect of natural cellulose microfibres and silica fume on the rheological, mechanical, and sustainability performance of 3D-printable mortars. Six mixes were prepared with 50% GGBS, 45% cement, and 5% silica fume, incorporating fibre dosages from 0% to 1%. Results showed that a 0.5% fibre dosage provided the most favourable balance. At this dosage, static yield stress increased to 9.35 Pa and thixotropy reached 8623 mPa·s, enhancing structuration for shape retention. Plastic viscosity remained stable at 4–5 Pa·s, ensuring adequate extrusion performance. Higher fibre dosages (≥0.75%) caused a significant increase in rheological resistance, with static yield stress reaching 208 Pa and thixotropy 135,342 mPa·s. This resulted in excessive structuration, fibre clustering, and poor extrudability. Compressive strength was achieved at 109.10 MPa (92% of silica fume-only mix) with 0.5% fibre. In comparison, flexural strength was 13.20 MPa at 0.5% fibre content and reduced gradually to 12.29 MPa at 1% fibre due to weak fibre–matrix bonding and porosity. Sustainability analysis confirmed that using 50% GGBS and 5% silica fume reduced embodied carbon compared to a 100% cement mix. This study also demonstrated that cellulose microfibres at 0.25–0.5% are optimal for balancing fresh properties, mechanical strength, and sustainability in 3D-printed mortars. Full article