Search Results (628)

It is known that geopolymer mortar exhibits high compressive strength but relatively low flexural strength, high brittleness, and poor toughness. Engineering practices for cement-based materials have demonstrated that incorporating fibers can effectively prevent the expansion of existing cracks and the formation of new ones in the materials. Adding polypropylene fibers to geopolymer mortar can, on the one hand, improve the crack resistance of the mortar, and on the other hand, enhance the impact resistance of the geopolymer mortar. In this paper, slag, metakaolin, and fly ash are utilized as silico-aluminous raw materials, standard sand is employed as aggregate, and a mixture of water glass and NaOH in a specific proportion is used as the alkali activator to prepare geopolymer mortar. Polypropylene fibers are incorporated to improve its mechanical properties. The effects of fiber length and mixing method on the mechanical properties of geopolymer mortar are studied to determine the optimal fiber length and mixing method. The mechanism of the mechanical properties of fiber-reinforced geopolymer mortar is analyzed by combining SEM. The research results indicate that the geopolymer mortar with 15 mm single-doped fibers exhibits the best flexural strength and toughness. In contrast, the geopolymer mortar with 12 mm single-doped fibers demonstrates the best compressive strength. The geopolymer with 9 mm and 18 mm hybrid-doped fibers has the best mechanical properties and is superior to the geopolymer mortar with single-doped fibers. Full article

As a result of global urbanization, the construction industry has mainly emitted CO₂ from ordinary Portland cement (OPC). Partially replacing cement with supplementary cementitious materials is a widely studied approach for reducing emissions. While previous studies have explored binary systems such as fly ash (FA)–cement and oyster shell powder (OSP)–cement, limited research has been conducted on ternary systems that combine FA, OSP, and cement. The differences in macro- and microsustainability performance between binary and ternary mixes remain unclear and require further exploration. To address this gap, this study verified the feasibility of using FA and OSP for partially replacing OPC in concrete. The environmental and mechanical performances of these materials were evaluated through macro- and microlevel experiments, as well as through life cycle assessments (LCAs). The results show that there is a synergistic effect in the FA-OSP-OPC ternary mixed cement (28-day strength: 40.44 MPa), which promotes the hydration of the three-component cement. Compared with the FA-OPC (28-day strength: 39.38 MPa) and OSP-OPC (28-day strength: 26.85 MPa) two-component cements, the strength is increased by 2.7% and 50.61%, respectively. At the same time, the resistivity of the three-component cement is also increased. The resistivity is increased by 19.27% ((50.69 − 42.5)/42.5) compared with the pure cement group. On this basis, the three-component cement also reduces carbon emissions by about 15% ((13.09 − 11.19)/13.09). FA-OSP-OPC ternary mixed cement improves strength and durability, reduces carbon emissions, and is an excellent new ternary mixed gel material that can be sustainably utilized. Full article

Given the significant impact of concrete’s compressive strength on structural service life, the development of accurate and efficient prediction methods is critically important. A hybrid machine learning modeling method based on the Whale Optimization Algorithm (WOA)-optimized XGBoost algorithm is proposed. Using 1030 sets of concrete mix proportion data covering eight key parameters—cement, blast furnace slag, fly ash, water, superplasticizer, coarse aggregate, fine aggregate, and curing age—the predictive performance of four models (linear regression, random forest, XGBoost, and WOA-XGBoost) was systematically compared. The results demonstrate that the WOA-XGBoost model achieved the highest goodness of fit (R² = 0.9208, MSE = 4.5546), significantly outperforming the other models, and exhibited excellent generalization capability and robustness. Feature importance and SHAP analysis further revealed that curing age, cement content, and water content are the key variables affecting compressive strength, with blast furnace slag showing a significant marginal diminishing effect. This study provides a high-precision data-driven tool for optimizing mix proportions and predicting the strength of complex-component concrete, offering significant application value in promoting the resource utilization of industrial waste and advancing the development of green concrete. Full article

This study developed a sustainable high-strength coal gangue backfill material for underground mining applications using coal gangue, fly ash, and cement as primary raw materials, with red mud (RM) as an alternative alkali activator. The mechanical properties of the backfill material were systematically optimized by adjusting coal gangue particle size and alkali activator dosage. The optimized formulation (coal gangue/fly ash/cement = 5:4:1, 3–6 mm coal gangue particle size, 5% RM, which named BF-6-5RM) achieved superior compressive strengths of 8.23 MPa (7 days) and 10.5 MPa (28 days), significantly exceeding conventional backfill requirements and outperforming a CaO-activated reference system (coal gangue/fly ash/cement = 5:4:1, 3–6 mm coal gangue particle size, 2% CaO, which named BF-6-2CaO). Microstructural and physicochemical analyses revealed that both formulations produced calcium silicate hydrate gels (C-S-H gels) and ettringite (AFt) as key hydration products, though BF-6-5RM exhibited a denser microstructure with well-developed ettringite networks and no detectable portlandite (CH), explaining its enhanced early-age strength. Environmental assessments confirmed effective heavy metal immobilization via encapsulation, adsorption, precipitation and substitution, except for arsenic (As), which exceeded Class III groundwater thresholds (DZ/T 0290-2015) due to elevated raw material content, displaying “surface wash-off, diffusion and depletion” leaching behavior. The findings confirm that red mud-based alkali activation is a viable technology for underground backfilling, provided it is coupled with arsenic control strategies like chemical stabilization or the selection of low-arsenic raw materials. This approach not only enables the resource utilization of hazardous industrial waste but also facilitates the production of backfill materials that combine both mechanical strength and environmental compatibility, thereby delivering dual economic and ecological benefits for sustainable mining practices. Full article

Fly ash is a commonly used mineral addition in construction engineering. Research on its different particle size distributions can help optimize material performance, promote resource utilization, and support environmental protection. In this study, the particle size of fly ash was used as a variable; fly ash with a single particle size was prepared by means of sieving, and the particle size was precisely controlled as a variable, thus avoiding the errors caused by the addition of multiple different particle sizes. Replacing 10% of the cement with fly ash to prepare cement mortar, the influence of fly ash particle size on the performance of cement mortar was investigated. The results show that the mortar incorporating fly ash with a particle size range of 10–20 μm achieves a 28-day compressive strength of 58.25 MPa and a flexural strength of 10.29 MPa. The hydration heat release rate of fly ash in the 10–20 μm range reaches a maximum of 1.84 mW/g, and the total hydration heat release peaks at 211.17 J/g at 70 h. The influence of fly ash particle size on the total hydration heat release is relatively small in the early stages but increases rapidly with prolonged hydration time. When the fly ash particle size is in the 10–20 μm range, the cement mortar exhibits the lowest total porosity at 12.88%, with the smallest average pore size of 27.1 nm and the smallest most probable pore size of 21.2 nm. This reduces harmful pores, increases the number of harmless pores, makes the cement mortar structure denser, and improves the durability of the mortar. The types of hydration products of different particle sizes of fly ash did not change. The smaller the particle size of fly ash, the more complete the volcanic ash reaction, promoting the hydration of mortar. Full article

Infrastructure development increasingly requires sustainable construction materials, with waste utilization serving as a key strategy to address this need. Employing eco-friendly materials with enhanced engineering properties not only mitigates the environmental impact of waste but also lowers the carbon footprint associated with cement production. Accordingly, this research aims to investigate the potential of enhancing the performance of municipal solid waste incineration ash (MSWIA) mortar through the incorporation of rice husk ash (RHA) as a supplementary cementitious material (SCM), thereby supporting the principles of a circular economy. The MSWIA mortar comprised 25% bottom ash (BA) and 5% fly ash (FA) as substitutes for fine aggregate and cement, respectively. Cement was then replaced with RHA at 5–30% to assess the influence of RHA on the properties of MSWIA mortars such as workability, strength development, and water absorption. Adding RHA led to a lower flow rate and setting time than mortar content-only MSWIA. Nonetheless, the various mechanical properties of MSWIA mortar, such as compressive strength, split tensile strength, and flexure strength, were found to be increased when the RHA quantity was used at 10% as a cement replacement. The water absorption of the mortar mixes was reduced by increasing RHA up to 15%. The test results revealed that the mortar’s microstructural properties were notably enhanced, and the UPV measurements confirmed the overall good quality of the mortar specimens. Therefore, incorporating RHA and MSWIA in construction not only enhances performance but also contributes to environmental sustainability by reducing the carbon dioxide emission and landfill waste. Full article

Geopolymers, as a novel class of low-carbon and eco-friendly cementitious material, exhibit outstanding durability and promote the resource utilization of industrial solid wastes. However, as a promising alternative to ordinary Portland cement, its susceptibility to carbonation-induced degradation may limit its widespread application. To address this challenge, this study systematically examined the effects of magnesium oxide (MgO) content and the metakaolin-to-fly ash ratio on the carbonation performance, mechanical properties, pH value, and microstructures of metakaolin–fly ash-based (MF-based) geopolymer pastes. The findings revealed that an increase in the fly ash ratio correlated with a decline in the compressive strength of MF-based geopolymer pastes. Conversely, the incorporation of MgO significantly enhanced the compressive strength, with higher fly ash ratios leading to more substantial improvements in strength. Furthermore, the addition of MgO and fly ash effectively mitigated the penetration of carbonation and the associated decrease in the pH value of the MF-based geopolymer pastes. Specifically, compared to the control group without MgO (M8F2-0%), MF-based geopolymer pastes with 4% and 8% MgO additions exhibited reductions in carbonation depth of 69.4% and 80.4%, respectively, after 28 days of carbonation, while pH values were observed to be 1.22 and 1.15 units higher, respectively. Additionally, microscopic structural analysis revealed that the inclusion of MgO resulted in a reduction in pore size, porosity, and mean pore diameter within the geopolymer pastes. This improvement was mainly attributed to the promotion of hydration processes by MgO, leading to the formation of fine Mg(OH)₂ crystals within the high-alkalinity pore solution, which enhances microstructural densification. In conclusion, the incorporation of MgO significantly improves the carbonation resistance and mechanical performance of MF-based geopolymers. It is recommended that future studies explore the long-term performance under combined environmental actions and evaluate the economic and environmental benefits of MgO-modified geopolymers for large-scale applications. Full article

The present study aims to develop 3D-structured adsorbents for carbon capture with the utilization of coal ash after its conversion into zeolites. For this purpose, printing paste mixtures with a viscosity of 800 Pa·s were developed based on an environmentally friendly and safe polymer binder filled with coal ash zeolite with the addition of bentonite as a filler. The optimal consistency of the printing mixtures for preserving the shape and dimensions of the 3D-printed structures was established. Various model configurations of the macrostructure of 3D adsorbents were developed, and the optimal settings of the extruding system for their printing were established. After calcination, the resulting 3D structures were studied using instrumental analysis techniques, investigating the influence of 3D structuring on the phase composition, surface characteristics, and adsorption capacity for CO₂ capture in comparison with the initial powder coal ash zeolite adsorbents. The role of compensating cations in terms of the adsorption ability of powders in 3D-printed adsorbents was investigated. The current study offers an innovative and previously unexplored approach to a more expedient and practically significant utilization of aluminosilicate solid waste and, in particular, coal ash, through their 3D structuring and outlines a new research and technological direction in the development of economically advantageous, technologically feasible, and environmentally friendly 3D adsorbents. Full article

Traditional landfill disposal of muck uses a significant amount of land and pollutes the environment, while current solidification methods heavily depend on energy-intensive cement. This study introduces a novel approach for synergistically solidifying muck using cement, fly ash, and steel slag, aiming to utilize waste resources and achieve low-carbon disposal. Experimental optimization identified the optimal ratio (cement:fly ash:steel slag = 2:2:1). The findings indicate that cement is crucial for early strength, while industrial waste materials enhance long-term performance through continued reactions. At a total solidifying agent content of 4–6%, the material exhibits optimal mechanical properties and durability, with only a 4% strength loss after 12 dry–wet cycles. Microscopic analysis indicates that several gels and polymers with cementing properties are produced, collectively enhancing the material’s structure. Additionally, this material effectively immobilizes heavy metals, including chromium, lead, arsenic, and cadmium, with leaching concentrations that are well below safety thresholds. This approach provides a dependable and eco-friendly method for large-scale disposal of construction waste muck and industrial solid waste, offering significant potential for engineering applications. Further studies could investigate additional solid waste types and formulations suitable for high-moisture materials like sludge. Full article

This article presents the results of a comprehensive investigation into geopolymer composites synthesized from fly ash, incorporating ground asphalt derived from reclaimed road pavement and quartz sand. The primary objective of this study was to elucidate the influence of mixture composition on the mechanical, physical, and microstructural characteristics of the developed materials. The innovative aspect of this research lies in the integration of two distinct filler types—mineral (quartz sand) and organic-mineral (milled asphalt)—within a single geopolymer matrix, while preserving key performance parameters required for engineering applications, including compressive and flexural strength, density, water absorption, and abrasion resistance. The experimental methodology encompassed the characterization of the raw materials by X-ray diffraction (XRD), chemical composition analysis via X-ray fluorescence (XRF), and assessment of particle size distribution. Additionally, the produced geopolymer materials underwent density determination, compressive and flexural strength measurements, abrasion testing, and mass water absorption evaluation. The chemical composition was further examined using XRF, and the surface morphology of the specimens was analyzed by scanning electron microscopy (SEM). The findings demonstrate that the incorporation of quartz sand enhances the density and mechanical strength of the composites, whereas the addition of recycled asphalt, despite causing a modest reduction in mechanical performance at elevated dosages, augments water resistance. Moreover, ternary composite material provide an optimal compromise between mechanical strength and durability under humid conditions. Overall, the results substantiate the feasibility of utilizing asphalt waste for the fabrication of functional and sustainable geopolymer materials suitable for construction applications. Full article

The research problem was to determine the possibility of aqueous mineral carbonation using fly ash from lignite fluidized bed combustion. Both direct and indirect routes were used. The innovative nature of the research consisted of conducting experiments at atmospheric pressure and ambient temperature (20 °C). The synthetic gas mixture with composition analogical to the flue gas (nitrogen and up to 16 vol.% of carbon dioxide) was used. The experiments proved that almost all CO₂ from the gas was chemically bound at pH > 12. The sequestration capacity of studied fly ash is about 55–76 g CO₂ per 1 kg of ash in the case of the indirect method, and 80–95 g CO₂ per 1 kg of ash for the direct route. These values are similar to those presented in the literature, but unlike most publications, they were obtained under ambient conditions, which can significantly reduce the costs of the process. Full article

Using systematic literature observations, this study explains how 3D printing technology is being applied to innovative sustainable construction (Systematic Literature Review). Additive manufacturing, also referred to as 3D printing technology, has greatly increased productivity and adoption in the building sector. The utilization of eco-friendly materials, enhancing sustainable building practices, and the environmental impact of 3D printing technology in comparison to conventional techniques are the three primary areas of attention for this study. By reducing material waste through additive manufacturing methods, 3D printing technology may employ alternative resources like fly ash, geopolymers, and limestone calcined clay (LC3) cement, which lowers carbon emissions considerably, according to observation data. This technology also speeds up the construction process, saves costs, and enables complex architectural designs that are difficult to achieve with conventional methods. There are still a number of issues, though, such as the high upfront expenditures of supplies and equipment and the long-term robustness of the molded structures that are produced. Nevertheless, 3D printing has enormous potential to transform building methods into more effective and ecologically friendly ones as a result of technological advancements and growing knowledge of desirability. This research provides valuable insights for stakeholders in supporting wider application of this technology to achieve sustainable development goals. Full article

As infrastructure construction expands, the massive consumption of traditional concrete materials has led to resource shortages and environmental pollution. Utilizing industrial wastes such as coal gangue and fly ash to produce high-performance concrete is an important pathway toward a greener construction industry. However, concrete incorporating high volumes of fly ash and coal gangue (i.e., high-volume fly-ash coal-gangue self-compacting concrete, CGSC) suffers from low strength and high brittleness due to the inherent deficiencies of its constituents. This study proposes using glass fiber-reinforced polymer (GFRP) tubes for external confinement to improve the axial compressive capacity and deformability of CGSC. A total of 27 concrete cylinders were prepared and tested under axial compression, with real-time acoustic emission (AE) monitoring. The variables examined include the coarse aggregate type (coal-gangue and natural gravel), GFRP tube thickness (5 mm and 8 mm), and fly-ash content (80%, 85%, 90%). The stress–strain response of each specimen and the failure evolution of internal cracks were recorded throughout the loading process. The results show that GFRP tube confinement markedly increases the axial strength and ductility of CGSC. AE features exhibited staged behavior that closely mirrored the stress–strain curves. This correspondence reveals the progression of internal cracks under confinement and indicates that AE is an effective tool for damage monitoring in such composites. The findings provide a new technical approach for the efficient reuse of solid waste in concrete and offer a theoretical and practical basis for applying FRP composite structures in underground support engineering. Full article

In this study, xanthan gum (XG)-modified coal-fly-ash-based cementitious materials were synthesized to realize the resource utilization of coal fly ash and to develop a low-carbon emission cementitious sealing material that can substitute cement-based sealing material to prevent coal fires. The optimal formulation for coal-fly-ash-based mining cementitious sealing material was developed using response surface methodology based on Box–Behnken Design. The optimized formulation was obtained with a coal fly ash-to-precursor ratio of 0.65, alkali-activator modulus of 1.4, and alkali-activator dosage of 7.5%. Under the optimal conditions, the initial and final setting time were 26 min and 31 min, respectively, fluidity was 245 mm, and the 7-day compressive strength approached 36.60 MPa, but there were still thermal shrinkage and cracking phenomena after heating. XG was then introduced to improve the thermal shrinkage and cracking of coal-fly-ash-based cementitious materials. Incorporating 1 wt.‰ XG was found to decrease the fluidity while maintaining the setting time and increasing the 1-day and 7-day compressive strength by 15.44% and 1.97%, respectively. The results demonstrated that the gels generated by XG cross-linking and coordinating with Al³⁺/Ca²⁺ were interspersed in the original C(N)-A-S-H gel network, which not only made the 1 wt.‰ XG modified coal-fly-ash-based cementitious material show minor expansion at ambient temperatures, but also improved the residual compressive strength, thermal shrinkage resistance and cracking resistance in comparison to unmodified cementitious material. However, due to the viscosity of XG and the coordination of Al³⁺ and non-terminal carboxyl groups in XG breaking the gel network, XG incorporation should not exceed 1 wt.‰ as the compressive strength and fluidity are decreased. Full article

This study advances alkali-activated cementitious materials (AACMs) by developing a ground-granulated blast furnace slag/high-calcium fly ash (GGBS/HCFA) composite that incorporates Tuokexun desert sand and by establishing a clear linkage between activator chemistry, mix proportions, curing regimen, and microstructural mechanisms. The innovation lies in valorizing industrial by-products and desert sand while systematically optimizing the aqueous glass modulus, alkali equivalent, HCFA dosage, and curing temperature/time, and coupling mechanical testing with XRD/FTIR/SEM to reveal performance–structure relationships under thermal and chemical attacks. The optimized binder (aqueous glass modulus 1.2, alkali equivalent 6%, and HCFA 20%) achieved 28-day compressive and flexural strengths of 52.8 MPa and 9.5 MPa, respectively; increasing HCFA beyond 20% reduced compressive strength, while flexural strength peaked at 20%. The preferred curing condition was 70 °C for 12 h. Characterization showed C-(A)-S-H as the dominant gel; elevated temperature led to its decomposition, acid exposure produced abundant CaSO₄, and NaOH exposure formed N-A-S-H, each correlating with strength loss. Quantitatively, acid resistance was weaker than alkali resistance and both deteriorated with concentration: in H₂SO₄, 28-day mass loss rose from 1.22% to 4.16%, with compressive/flexural strength retention dropping to 75.2%, 71.2%, 63.4%, and 57.4% and 65.3%, 61.6%, 58.9%, and 49.5%, respectively; in NaOH (0.2/0.5/0.8/1.0 mol/L), 28-day mass change was +0.74%, +0.88%, −1.85%, and −2.06%, compressive strength declined in all cases (smallest drop 7.77% at 0.2 mol/L), and flexural strength increased at lower alkalinity, consistent with a pore-filling micro-densification effect before gel dissolution/cracking dominates. Practically, the recommended mix and curing window deliver structural-grade performance while improving high-temperature and acid/alkali resistance relative to non-optimized formulations, offering a scalable, lower-carbon route to utilize regional desert sand and industrial wastes in durable cementitious applications. Full article