Search Results (159)

This study investigates the feasibility of using volcanic lapillus as a supplementary cementitious material (SCM) in mortar production to improve the sustainability of the cement industry. Cement production is one of the main sources of CO₂ emissions, mainly due to clinker production. Replacing clinker with SCMs, such as volcanic lapillus, can reduce the environmental impact while maintaining adequate mechanical properties. Experiments were conducted to replace up to 20 wt% of limestone Portland cement with volcanic lapillus. Workability, compressive strength, microstructure, resistance to alkali-silica reaction (ASR), sulfate, and chloride penetration were analyzed. The results showed that up to 10% replacement had a minimal effect on mechanical properties, while higher percentages resulted in reduced strength but still improved some durability features. The control sample cured 28 days showed a compressive strength of 43.05 MPa compared with 36.89 MPa for the sample containing 10% lapillus. After 90 days the respective values for the above samples were 44.76 MPa and 44.57 MPa. Scanning electron microscopy (SEM) revealed good gel–aggregate adhesion, and thermogravimetric analysis (TGA) confirmed reduced calcium hydroxide content, indicating pozzolanic activity. Overall, volcanic lapillus shows promise as a sustainable SCM, offering CO₂ reduction and durability benefits, although higher replacement rates require further optimization. Full article

Quarry dust (QD) landfill causes environmental issues that cannot be ignored. In this study, we systematically explore its potential application as a supplementary cementitious material (SCM) in cemented paste backfill (CPB), revealing the activated mechanism of modified QD (MQD) and exploring the hydration process and workability of CPB containing QD/MQD. The experimental results show that quartz, clinochlore and amphibole components react with CaO to form reactive dicalcium silicate (C₂S) and amorphous glass phases, promoting pozzolanic reactivity in MQD. QD promotes early aluminocarbonate (M_c) formation through CaCO₃-derived CO₃²⁻ release but shifts to hemicarboaluminate (H_c) dominance at 28 d. MQD releases active Al³⁺/Si⁴⁺ due to calcination and deconstruction, significantly increasing the amount of ettringite (AFt) in the later stage. With the synergistic effect of coarse–fine particle gradation, MQD-type fresh backfill can achieve a 161 mm flow spread at 20% replacement. Even if this replacement rate reaches 50%, a strength of 19.87 MPa can still be maintained for 28 days. The good workability and low carbon footprint of MQD-type backfill provide theoretical support for—and technical paths toward—QD recycling and the development of low-carbon building materials. Full article

Fluidized solidified soil (FSS) has emerged as a promising material for marine pile scour remediation, yet its limited construction window and vulnerability to hydraulic erosion before sufficient curing constrain its broader application. This study systematically evaluates FSS formulations based on dredged sediment, cement partially replaced by silica fume (i.e., 0%, 4%, 8%, and 12%), and quicklime activation under three water–solid ratios (WSR, i.e., 0.525, 0.55, and 0.575). Experimental assessments included flowability tests, unconfined compressive strength, direct shear tests, and microstructural analysis via XRD and SEM. The results indicate that SF substitution significantly mitigates flowability loss during the 90–120 min interval, thereby extending the operational period. Moreover, the greatest enhancement in mechanical performance was achieved at an 8% SF replacement: at WSR = 0.55, the 3-day UCS increased by 22.78%, while the 7-day cohesion and internal friction angle rose by 13.97% and 2.59%, respectively. Microscopic analyses also confirmed that SF’s pozzolanic reaction generated additional C-S-H gel. However, the SF substitution exhibits a pronounced threshold effect, with levels above 8% introducing unreacted particles that disrupt the cementitious network. These results underscore the critical balance between flowability and early-age strength for stable marine pile scour repair, with WSR = 0.525 and 8% SF substitution identified as the optimal mix. Full article

The cements industry is increasingly under pressure to reduce carbon emissions while maintaining performance standards. Limestone calcined clay cement (LC³) presents a promising low-carbon alternative; however, its performance depends significantly on the type and reactivity of clay used. This study investigates the effect of three common low-grade clay minerals—kaolinite, montmorillonite, and illite—on the behavior of LC³ blends. The clays were thermally activated and characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray fluorescence spectroscopy (XRF), and Blaine air permeability testing to evaluate their mineralogical composition, thermal behavior, chemical content, and fineness. Pozzolanic reactivity was assessed using the modified Chapelle test. Microstructural development was examined through scanning electron microscopy (SEM) of the hydrated specimens at 28 days. The results confirmed a strong correlation between clay reactivity and hydration performance. Kaolinite showed the highest reactivity and fineness, contributing to a dense microstructure with reduced portlandite and enhanced formation of calcium silicate hydrate. Montmorillonite demonstrated comparable strength and favorable hydration characteristics, while illite, though less reactive initially, showed acceptable long-term behavior. Although kaolinite delivered the best overall performance, its limited availability and higher cost suggest that montmorillonite and illite represent viable and cost-effective alternatives, particularly in regions where kaolinite is scarce. This study highlights the suitability of regionally available, low-grade clays for use in LC³ systems, supporting sustainable and economically viable cement production. Full article

As a promising and sustainable construction material, alkali-activated slag lightweight high-strength concrete (AAS-LWHSC) may be influenced by lightweight aggregate (LWA) content. In this study, the effects of hollow glass microspheres (HGM) replacing granulated ground blast furnace slag (GGBFS) under varying LWA dosages on the workability, dry apparent density, mechanical properties, and microstructure of AAS-LWHSC were investigated. The results indicated that the dry density of concrete was significantly reduced by HGM, while the “ball-bearing” effect of HGM was observed to enhance workability at a dosage of 6%. The 7-day mechanical properties of AAS-LWHSC were found to decline progressively with increasing HGM content. However, at the shale ceramsite sand replacement rates of 35% and 65%, the incorporation of 6% HGM slightly improved the 28-day mechanical properties. Due to the absence of the water-releasing effect from shale ceramsite, the pozzolanic reactions of HGM were restricted, resulting in coarse hydration products and a reduction in the mechanical performance of AAS-LWHSC. Full article

This study investigates the use of Glass Fine Aggregate (GFA) and Fly Ash (FA) in mortar for Alkali–Silica Reaction (ASR) mitigation through a multidimensional evaluation. GFA was used to replace river sand in 20% increments up to 100%, while FA replaced cement at 10%, 20%, and 30%. Three GFA size ranges were considered: <1.18 mm, 1.18–4.75 mm, and a combined fraction of <4.75 mm. At 100% replacement, <1.18 mm GFA reduced ASR expansion to 0.07%, compared to 0.2% for <4.75 mm and 0.46% for 1.18–4.75 mm GFA. It also improved long-term strength by 25% from 28 days to 6 months due to pozzolanic activity. However, refining GFA to below 1.18 mm increased environmental impacts and resulted in a 4.2% increase in energy demand due to the additional drying process. Incorporating 10% FA reduced ASR expansion to 0.044%, had no significant effect on strength, and decreased key environmental burdens such as toxicity by up to 18.2%. These findings indicate that FA utilisation offers greater benefits for ASR mitigation and environmental sustainability than further refining GFA size. Therefore, combining <4.75 mm GFA with 10% FA is identified as the optimal strategy for producing durable and sustainable mortar with recycled waste glass. Full article

Wood ash is a promising supplementary cementitious material (SCM) due to its inherent pozzolanic properties. Intensive grinding has been shown to enhance this aspect and reduce the negative effects of variability in the chemical composition. This study investigated the influence of grinding through ball milling on the pozzolanic properties of wood ash. Four different types of wood ash were studied, each subjected to grinding durations of 10 and 20 min. Coal fly ash was used as a reference material. The pozzolanic activity of raw and ground wood ashes was evaluated using the strength activity index (SAI), the Frattini test, the R3 test, thermogravimetric analysis (TGA/DTG), X-ray diffraction (XRD) analysis, and scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS). The results indicated that both 10 min and 20 min grinding durations enhanced the reactivity and compressive strength. However, the 10 min grinding duration showed better overall performance than 20 min grinding, likely due to reduced agglomeration and more effective particle refinement. For calcium-rich wood ashes, the reactivity was linked to the hydraulic properties rather than the pozzolanic properties. Full article

This study systematically investigates the utilization of marble industry waste—waste marble powder (WMP) as partial cement replacement and waste marble aggregates (WMA) as partial fine aggregate replacement—in self-compacting concrete (SCC). A detailed experimental program evaluated the effects of various replacement levels (5%, 10%, and 20% for WMP; 20%, 30%, and 40% for WMA) on compressive strength and durability, particularly resistance to aggressive sulfuric acid environments. Results indicated that a 5% WMP replacement increased compressive strength by 4.9%, attributed primarily to the filler effect, whereas higher levels (10–20%) led to strength reductions due to limited pozzolanic activity and cement dilution. In contrast, WMA replacement consistently enhanced strength (maximum increase of 11.5% at 30% substitution) due to improved particle packing and aggregate-paste interface densification. Durability tests revealed significantly reduced compressive strength losses and mass loss in marble-containing mixtures compared to control samples, with optimal acid resistance observed at 20% WMP and 40% WMA replacements. A comprehensive life cycle assessment demonstrated notable reductions in environmental impacts, including up to 20% decreases in Global Warming Potential (GWP) at 20% WMP replacement. A desirability-based eco-cost-mechanical optimization—simultaneously integrating mechanical strength, environmental indicators, and production cost—identified the 10% WMP substitution mix as the most sustainable option, achieving optimal balance among key performance criteria. These findings underscore the significant potential for marble waste reuse in SCC, promoting environmental sustainability, resource efficiency, and improved concrete durability in chemically aggressive environments. Full article

The construction industry’s escalating environmental footprint, coupled with the underutilization of construction waste streams, necessitates innovative approaches to sustainable material design. This study investigates the dual functionality of recycled clay brick powder (RCBP) as both a supplementary cementitious material (SCM) and an alkali–silica reaction (ASR) inhibitor in hybrid mortar systems incorporating recycled glass (RG) and recycled clay brick (RCB) aggregates. Leveraging the pozzolanic activity of RCBP’s residual aluminosilicate phases, the research quantifies its influence on mortar durability and mechanical performance under varying substitution scenarios. Experimental findings reveal a nonlinear relationship between RCBP dosage and mortar properties. A 30% cement replacement with RCBP yields a 28-day activity index of 96.95%, confirming significant pozzolanic contributions. Critically, RCBP substitution ≥20% effectively mitigates ASRs induced by RG aggregates, with optimal suppression observed at 25% replacement. This threshold aligns with microstructural analyses showing RCBP’s Al³⁺ ions preferentially reacting with alkali hydroxides to form non-expansive gels, reducing pore solution pH and silica dissolution rates. Mechanical characterization reveals trade-offs between workability and strength development. Increasing RCBP substitution decreases mortar consistency and fluidity, which is more pronounced in RG-RCBS blends due to glass aggregates’ smooth texture. Compressively, both SS-RCBS and RG-RCBS mortars exhibit strength reduction with higher RCBP content, yet all specimens show accelerated compressive strength gain relative to flexural strength over curing time. Notably, 28-day water absorption increases with RCBP substitution, correlating with microstructural porosity modifications. These findings position recycled construction wastes and glass as valuable resources in circular economy frameworks, offering municipalities a pathway to meet recycled content mandates without sacrificing structural integrity. The study underscores the importance of waste synergy in advancing sustainable mortar technology, with implications for net-zero building practices and industrial waste valorization. Full article

Over 2 million tonnes of ceramic waste are generated annually in South Africa, with the majority disposed of in landfills, contributing to environmental degradation. Meanwhile, researchers are actively seeking sustainable alternatives to Portland cement (PC), which is associated with significant environmental challenges. Ceramic waste powder (CWP) refers to finely milled ceramic waste and powder derived from the polishing and finishing stages of ceramic production. This review examines the potential of CWP as a partial replacement for PC in concrete, focusing on its effects on workability, mechanical durability, and microstructural properties. The findings indicate that moderate replacement levels (up to 20%) enhance the compressive and flexural strengths of concrete. However, these benefits are not consistently reported across all studies. Additionally, CWP improves the microstructural properties of the concrete. This is probably due to the pozzolanic reactions of CWP, which result in a denser concrete matrix and enhanced long-term durability. Notable durability benefits include reduced water absorption, increased resistance to chemical attacks, and improved thermal insulation. However, the performance of concrete with higher CWP replacement levels (above 30%) remains unclear. Some studies have reported strength reductions and increased susceptibility to durability loss at this level. Further studies should focus on clarifying its pozzolanic reactivity, durability in aggressive environments, and optimum replacement percentage. Full article

This study focuses on the production and characterization of activated carbons derived from the carbonaceous residue obtained through the catalytic pyrolysis of waste tires. A catalytic pyrolysis process was conducted at 450 °C and 575 °C, employing two zeolitic catalysts, the commercial ZSM-5 and a synthesized zeolite (PZ2), developed from natural pozzolan, which played a key role in the pyrolysis performance and the quality of the resulting carbons. After pyrolysis, the solid residues were chemically activated using KOH to improve their porous structure and surface characteristics. Comprehensive characterization was carried out, including textural properties (BET surface area and porosity) and morphological (SEM) analysis of the activated carbons, as well as crystallinity evaluation (XRD) of the zeolitic catalysts. The BET surface areas of activated carbons PZ2-T1-AK and PZ2-T2-AK reached 608.65 m²/g and 624.37 m²/g, respectively, values that surpass those reported for similar materials under comparable activation conditions. The developed porous structure suggests strong potential for applications in adsorption processes, including pollutant removal. These findings demonstrate the effectiveness of zeolite-catalyzed pyrolysis, particularly using PZ2, as a sustainable strategy for transforming tire waste into high-performance adsorbent materials. This approach supports circular economy principles through innovative waste valorization and offers a promising solution to an environmental challenge. Full article

Soil stabilizers are environmentally friendly engineering materials that enable efficient utilization of local soil-water resources. The application of nano-modified stabilizers to reinforce loess can effectively enhance the microscopic interfacial structure and improve the macroscopic mechanical properties of soil. This study employed nano-SiO₂ and nano-CaCO₃ to modify cement-based soil stabilizers, investigating the enhancement mechanisms of nanomaterials on stabilizer performance through compressive and flexural strength tests combined with microscopic analyses, including SEM, XRD, and FT-IR. The key findings are as follows: (1) Comparative analysis of mortar specimen strength under identical conditions revealed that nano-SiO₂ generally demonstrated superior mechanical enhancement compared to nano-CaCO₃ across various curing ages (1–3% dosage). At 1% dosage, the compressive strength of both modified stabilizers increased with curing duration. Early-stage strength differences (3 days) remained below 3% but showed a significant divergence with prolonged curing: nano-SiO₂ groups exhibited 10.3%, 11.3%, and 7.2% higher compressive strengths than nano-CaCO₃ at 7, 14, and 28 days, respectively. (2) The strength enhancement effect of nano-SiO₂ on MBER soil stabilizer followed a parabolic trend within 1–3% dosage range, peaking at 2.5% with over 15% strength improvement. (3) The exceptional performance of nano-SiO₂ originates from its high reactivity and ultrafine particle characteristics, which induce nano-catalytic hydration effects and demonstrate strong pozzolanic activity. These properties accelerate hydration processes while promoting the formation of interlocking C-S-H gels and hexagonal prismatic AFt crystals, ultimately creating a robust three-dimensional network that optimizes interfacial structure and significantly enhances strength characteristics across curing periods. These findings provide scientific support for the performance optimization of soil stabilizers and their sustainable applications in eco-construction practices. Full article

Enhancing the utilization rate of waste glass in concrete is crucial for achieving solid waste reduction and low carbon emissions in the construction industry. This study employs the method of simultaneously replacing fine aggregate and cementitious materials in concrete with glass sand and glass powder to prepare composite waste glass concrete (CGC). The compressive strength, alkali–silicate expansion, and thermal properties of CGC were investigated experimentally. The experimental results show that the pozzolanic activity of fine glass powder in CGC can effectively mitigate the ASR reaction, enhance glass utilization, and allow the glass content to reach up to 17.79% of the total concrete mass. The thermal conductivity of the compounded waste glass concrete decreased linearly with increasing temperature, and the specific heat capacity showed three distinct peaks in the range of 180–800 °C, which were caused by chemical dehydration, quartz phase transition, and CaCO₃ decarbonization, respectively. Furthermore, to examine the impact of replacement mode on the high-temperature resistance of waste glass concrete, the residual strength, physical properties, and microstructure of the concrete were evaluated. It was found that the residual strength ratio of CGC (0.73) exhibited a distinct advantage at 600 °C. At this time, the melting effect of glass can reduce the pore size of concrete and transform large pores into capillary pores. However, as the temperature rises to 800 °C, the melting effect of glass no longer alleviates the high-temperature damage to concrete, and the degree of decomposition of hydration products determines the concrete strength. Full article

Black cotton soil (BCS) is unsuitable for construction due to its high plasticity, low shear strength, and significant volume changes upon wetting and drying. The present study investigates the effectiveness of an alkali-activated coconut husk ash (CHA) binder in improving the geotechnical properties of BCS. CHA is derived from coconut husk and serves as a sustainable binder. Microstructural characterization of untreated and CHA-treated BCS was carried out using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The specific surface area (SSA) and porosity were evaluated using nitrogen gas adsorption methods based on the Brunauer–Emmett–Teller (BET) and Langmuir techniques. The Barrett–Joyner–Halenda (BJH) method demonstrated a decrease in mean pore diameter from 6.7 nm to 6.2 nm following CHA treatment. The SSA diminished from 40.94 m²/g to 25.59 m²/g, signifying the development of calcium silicate hydrate (C-S-H) gels that occupied the pore spaces. The formation of pozzolanic reaction products enhanced the microstructural integrity of the treated soil. Unconfined compressive strength (UCS) test results at 24 h and 28 days of curing for CHA-treated soil have been incorporated to analyze the optimum binder content. The UCS values enhanced significantly from 182 kPa to 305 kPa and 1030 kPa, respectively, at 9% binder content after 24 h and 28 days of curing. The microstructural and mechanical strength test analysis results indicated that CHA is a feasible and environmentally sustainable substitute for BCS stabilization. CHA-based AAB will be an eco-friendly alternative to cement and lime, reducing CO₂ emissions and construction costs. Full article

This study investigates the influence of various cementitious materials on the performance of alkali-activated green ultra-high performance concrete (GUHPC). Alkali-activated GUHPC was prepared by substituting cement, quartz powder, and limestone powder with slag powder and fly ash. The mechanical properties, durability, hydration products, and microstructure were systematically analyzed. The results demonstrate that, with a cement dosage of 264 kg/m³, the alkali-activated GUHPC incorporating 40% slag powder and 28% fly ash as cement replacements exhibited superior mechanical performance, achieving compressive and tensile strengths of 165.3 MPa and 7.7 MPa, respectively, after curing. The GUHPC displayed a dense internal structure with an extremely low porosity of 6.76%, along with superior impermeability and frost resistance compared to conventional UHPC. Slag powder exhibited high pozzolanic reactivity under alkali activation, enabling effective cement replacement. These findings provide valuable insights for the formulation of alkali-activated GUHPC. Full article