Search Results (121)

Granulated blast furnace slag is a commonly used supplementary cementitious material in cement-based materials. The raw materials for ironmaking and the cooling process affect its composition, thereby influencing its reactivity. Three types of slag were selected and incorporated at replacement ratios of 15%, 30%, and 50% to investigate the influence of chemical composition on the activity index of slag at different ages and the mechanisms. The results indicate that in the early hydration stage, slag primarily plays a mechanical filling and dilution role (inert volumetric occupation without significant heterogeneous nucleation), while the pozzolanic effect dominates at later stages. Al₂O₃ in the slag is activated at early ages to form ettringite; at replacement ratios of 30%, C-A-S-H gel is also formed at later ages; when the replacement ratio reaches 50%, the significant reduction in cement clinker content leads to dropping in system alkalinity—corresponding to a 50% reduction in cement-derived Ca(OH)₂, the activation of Al₂O₃ in the slag is not significant at early ages. The effects of glass content, alkali content, specific surface area, CaO + MgO content, quality coefficient, and basicity coefficient on the reactivity become prominent at longer ages. No additional crystalline phases beyond those present in pure cement paste were detected in the cement paste after slag incorporation. This study provides a theoretical basis and data support for the high-value utilization of industrial solid waste in green building materials. Full article

This study presents a comprehensive assessment of high-temperature performance, economic viability, and environmental sustainability of alkali-activated slag paste (AASB) incorporating municipal solid waste incineration bottom ash (MSWI-BA). The research systematically evaluates the effects of MSWI-BA content (0–12%), alkali content (2–6% Na₂O equivalent), water glass modulus (Ms = 0.75–1.75), and activator type on key performance metrics, both resource recovery and carbon reduction goals. Results show that the optimized formulation (6% MSWI-BA, 4% Na₂O, Ms = 1.5) achieves superior high-temperature resilience, retaining 76% of its initial compressive strength after 800 °C exposure—a stark contrast to OPC, which undergoes near-complete strength loss. Economic analysis reveals that while MSWI-BA offers an 88% reduction in raw precursor cost, the optimized AASB incurs a modest 3.7% total material cost premium over OPC, which is offset by its long-term sustainability benefits. Furthermore, a life-cycle assessment demonstrates that AASB has a 66.95% lower carbon footprint than OPC. Full article

Silicomanganese slag (SiMnS), a Mn-bearing by-product from silicomanganese alloy production, is often stockpiled in large quantities and may pose environmental concerns due to potential metal leaching. This study develops an OPC-rich hybrid SiMnS–steel slag–fly ash–OPC-activated composite binder, referred to as SMSAB, in which OPC accounts for 55% of the solid precursor mass. Different alkali contents and sodium silicate moduli were investigated, and the optimised paste was characterised in terms of mechanical strength, reaction products, pore structure, carbon-footprint and heavy-metal leaching. The best performance was obtained at an alkali content of 4% and a sodium silicate modulus of 1.0, giving 28-day compressive and flexural strengths of 65.13 MPa and 3.37 MPa, respectively. XRD, SEM-EDS, FTIR and MIP results showed that the main reaction products were C-(A)-S-H, N-A-S-H and C-N-A-S-H gels, which refined the pore structure and produced a dense matrix. The reduction in Mn leaching may be associated with physical encapsulation, possible charge-balancing interactions within gel structures, changes in Mn-related bonding environments and the presence of Mn-bearing phases. Leaching concentrations of Zn, Mn, Cr, Cu and Ni satisfied the Grade III groundwater limits used in China. The calculated carbon intensity of SMSAB was 3.97 kg·(m³·MPa)⁻¹, indicating a favourable strength-to-emission balance compared with the reference systems considered. It should be noted that the present work examines paste specimens only; aggregate skeleton, traffic loading, freeze–thaw cycling and wet–dry/moisture cycling were not included. Therefore, the results demonstrate binder-level potential rather than direct qualification of SMSAB as a pavement base or subbase material. Full article

This study investigates the feasibility of utilising alkali-activated slag (AAS) and construction demolition waste (CDW) as cemented paste backfill materials. The fluidity, unconfined compressive strength, bleeding rate, and sulfate resistance of AAS-CDW backfill systems were systematically analysed. Hydration mechanisms were characterised using SEM-EDS and XRD. A novel backfill system and application process were developed and implemented in Jining Coal Mine, Shandong Province. Results indicate that a 30% waste red brick addition enhances 28-day compressive strength by 9.3% and reduces the bleeding rate by 32%, while a 10% fly ash addition optimises slurry fluidity. Notably, the AAS-based backfill exhibits superior mechanical properties and sulfate resistance compared to ordinary Portland cement (OPC)-based systems. The 28-day compressive strength of the AAS backfill reached 5.31 MPa, which is 53.4% higher than that of the OPC backfill, and its strength loss rate after sulfate attack was reduced by 13%. The solid waste utilisation rate of the AAS backfill approaches 100%. Hydration products primarily comprise ettringite (Aft), C-A-S-H gel, and hydrotalcite (HT), resulting in higher compactness than OPC-RA mixtures. Full article

This study systematically examines the fluidity, setting time, mechanical properties, and microstructural evolution of metakaolin-based geopolymer grouting materials with a relatively high water-to-solid (W/S) ratio window. A four-factor, three-level orthogonal experimental design was employed to identify the dominant factors and main effect trends of W/S ratio, alkali dosage, water glass modulus (Ms, molar ratio of SiO₂ to Na₂O in alkali solution), and steel slag content on the material’s performance. The results indicated that the W/S ratio predominantly governed fluidity, while the alkali content was the primary controlling factor for setting time and early-age strength. An intermediate range of water glass modulus with a value of 1.6 provided balanced performance. The incorporation of steel slag with a range of 10–20% showed an age-dependent contribution: it not only tended to improve the rheology of the paste but also the later-age strength. XRD, FTIR, and SEM/EDS results suggested that the hardened binders were dominated by amorphous products, where alumimosilicate gel (N-A-S-H) and Ca-containing gel (C-S-H/C-A-S-H) may coexist depending on calcium availability and activator chemistry. The proposed parameter ranges are valid within the studied design space and provide guidance for the mix design of high-W/S geopolymer grout. Full article

Utilizing waste red-clay brick powder (WRCBP) as a precursor for manufacturing geopolymers is increasingly popular due to its environmental and economic benefits. However, the geopolymerization of this waste remains insufficiently explored. This study evaluates the differences in physical–mechanical properties and microstructural evolution of WRCBP- and fly ash (FA)-based geopolymers to determine the reactivity of WRCBP. Mineral admixtures, including granulated blast furnace slag (GF) and metakaolin (MT), were incorporated with WRCBP to fabricate geopolymer pastes, while FA was used in parallel for comparison. The effects of activator modulus (1.2 and 1.4 for Na₂SiO₃) and curing conditions (65 °C and 90 °C) on the mechanical and microstructural performance of the prepared pastes were investigated through water demand analysis, compressive strength testing, mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM). The results indicate that WRCBP-based pastes achieved a comparable compressive strength (39.8 MPa) under appropriate alkali-activated and curing conditions relative to FA-based pastes (42.5 MPa). The modulus of the alkaline activator exerted a greater influence on strength development than the raw material composition. For both WRCBP- and FA-based pastes, 65 °C was identified as a more suitable curing temperature. Moreover, compared with FA-based pastes, pastes produced using WRCBP provide enhanced social and economic benefits. Overall, this study confirms that high-performance binders can be engineered by incorporating WRCBP, thereby supporting the development of sustainable low-carbon construction materials. Full article

Waste stone powder, as a solid waste resource, is characterized by its large volume, wide distribution, and low utilization rate. Its resource utilization is one of the important approaches to achieving closed-loop recycling development in the stone industry. This study aims to utilize waste stone powder as a mineral admixture in the preparation of alkali-activated cementitious materials, investigating the influence of parameters such as waste stone powder content, water-binder ratio, and Na₂O content on the mechanical properties, fluidity, setting time, and shrinkage behavior of the cementitious materials. The results indicate that both waste stone powder and the water-binder ratio can effectively improve the setting time and fluidity of the paste. However, higher waste stone powder content leads to more severe shrinkage, and a calculation model for material shrinkage was established. The optimal mechanical properties for alkali-activated slag samples were achieved with a Na₂O content of 8%, waste stone powder content of 16%, and a water-binder ratio of 0.45. For alkali-activated metakaolin samples, a waste stone powder content of 16% resulted in superior mechanical performance. Furthermore, the failure of all material samples was brittle, primarily exhibiting typical splitting failure. Based on damage theory, a calculation model for the load–displacement curve of the material was developed, providing reference and support for further research and application of this material Full article

This study presents the optimisation of an alkali-activated binder produced from ground granulated blast furnace slag (GGBFS) and potassium-rich sunflower husk ash (SHA), by varying SHA content, curing regime, and mixing procedure. Both materials are locally available in the Republic of Serbia. The influence of SHA content (15%, 25%, and 35% by mass of GGBFS) and curing conditions (ambient and 65 °C) on hydration products, workability, and compressive strength was examined. The water-to-binder ratio and GGBFS content were kept constant, and a one-part alkali activation approach was employed using untreated SHA. Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were performed on paste samples, after 2, 7 and 28 days of curing, while workability and compressive strength of mortars were measured after 7 and 28 days. Increasing SHA content enhanced the formation of C-S-H and C-A-S-H gels, resulting in a consistent rise in compressive strength, from 26.6 MPa to 36.2 MPa after 7 days and from 46.2 MPa to 55.1 MPa after 28 days of ambient curing. Workability was slightly reduced with increasing SHA content, resulting in flow diameters of 156.04 mm (15% SHA), 154.10 mm (25% SHA) and 152.76 mm (35% SHA). Curing at 65 °C accelerated early strength gain for 33% to 39% but produced lower 28-day strengths than ambient curing. Additionally, for the optimal mix, SHA was also pre-immersed in water for varying durations to assess its effect on workability, compressive strength, and potassium ion leaching. This pretreatment increased compressive strength by up to 14.7%, depending on immersion time, but reduced workability by up to 15.5%. The novelty of the research is reflected in attaining the highest 28-day compressive strength of 55 MPa (for 25% SHA by mass of GGBFS), under ambient curing, without SHA pretreatment or immersion, highlighting the potential for low-energy, sustainable binder systems using agricultural and industrial by-products. Full article

Geopolymer materials possess several outstanding advantages, including the wide availability of raw materials, an energy-saving and environmentally friendly production process, and excellent engineering technical performance. They are regarded as a new type of green building material that can achieve high-value-added resource utilization of industrial solid waste. They are one of the current research hotspots in the field of materials. Fly ash and slag, the most common industrial wastes in China, have been discharged in large quantities, significantly impacting the country’s ecological environment. Based on this, this paper primarily investigates the mechanical properties and strength formation mechanism of geopolymer paste to develop geopolymer materials with enhanced mechanical properties. This research uses metakaolin as the silicate raw material and uses sodium silicate mixed with NaOH as the alkali activator to prepare geopolymer paste. By adding fly ash and slag, the mechanical properties of the geopolymer paste are improved. The effects of the alkali activator modulus, Na₂O equivalent, and content of fly ash and slag on the setting time and strength of geopolymer paste are studied. XRD, FTIR, and SEM are employed to characterize the phase, molecular structure, and microscopic morphology of geopolymer paste, as well as to analyze the microstructure and reaction mechanism of these materials. The results show that the setting time of the geopolymer increases with the increase in modulus and shortens with the increase in Na₂O equivalent. Fly ash and slag, respectively, act as retarders and early strength promoters. The ratio of n(SiO₂)/n(A1₂O₃) (that is, the modulus of the alkali activator) of the geopolymer is an important factor affecting its strength. The metakaolin and fly ash–slag–metakaolin exhibit the best mechanical properties when their molar ratios are 2.97 and 3.26, respectively. Through microscopic characterization using XRD, FTIR, and SEM, it is observed that fly ash–slag–metakaolin exhibits the most complete polymerization reaction, generates the most amorphous silicate aluminosilicate gel, and displays the best inter-gel bonding effect, resulting in the best mechanical properties. Full article

Alkali-activated materials (AAMs) offer a promising low-carbon alternative to Portland cement, but their development has been dominated by fly ash and slag, whose availability is increasingly limited. This research explores waste brick powder (WBP) and metakaolin residue (RN), two abundant yet underutilized by-products, as blended precursors for sustainable binder design. The novelty lies in demonstrating how complementary chemistry between crystalline-rich WBP and amorphous RN can overcome the drawbacks of single-precursor systems while valorizing construction and industrial residues. Pastes were prepared with varying WBP/RN ratios, activated with alkaline solutions, and characterized by Vicat setting tests, isothermal calorimetry, XRD with Rietveld refinement, MIP, SEM, and mechanical testing. Carbon footprint analysis was performed to evaluate environmental performance. Results show that WBP reacts very rapidly, causing flash setting and limited long-term strength, whereas the incorporation of 30–50% RN extends setting times, sustains dissolution, and increases amorphous gel formation. These changes refine the formed reaction products, leading to compressive strengths up to 39 MPa and flexural strengths of 8 MPa at 90 days. The carbon footprint of all blends remained 392–408 kg CO₂e/m³, thus providing about a 60% improvement compared to conventional Portland cement paste. The study establishes clear design rules for waste-derived blended precursors and highlights their potential as circular, low-carbon binders. Full article

The goal of this paper is to assess the evolution of the autogenous strains as well as the thermal strains (thanks to the assessment of the coefficient of thermal expansion) of alkali-activated slag-based materials at early age. The effect of the sand and the coarse aggregates on the paste and mortar scale to upscale to mortar and concrete, respectively, has been investigated as a function of the age of the material. The restraint imposed by the sand on the paste seemed more significant than that of the coarse aggregate on the mortar. In addition, the long-term autogenous strains have been monitored on the mortar scale. These results revealed a separation into groups based on the solution concentration. Different testing methods were also compared. Thermal and autogenous strains were monitored with a customized testing device where the thermal variations are controlled. These devices were the horizontal corrugated tubes method (for tests on paste and mortar scales) and the vertical corrugated tubes method (for tests on mortar and concrete scales). Depending on the compositions (lower concentration), good correlations can be obtained between the two testing methods. Moreover, the autogenous strain of two different specimen sizes was also assessed manually (initially for the long-term), but early-age comparison showed good correlation for lower solution-to-binder ratios. On the concrete scale, a correlation based on the modified equations from the standards was established between the compressive strength and the tensile strength, obtained from the splitting tensile test. Full article

Cementitious materials are susceptible to water ingress due to their hydrophilicity and porous microstructure, which can cause premature destruction and compromise long-term durability. Integral hydrophobic modification using alkyl silanes is an effective strategy for enhancing water resistance, while the influence of different silanes on early-age properties (within the first 7 d) of various binder systems remains unclear. This study investigates the rheology, flowability, setting behavior, reaction kinetics, compressive strength, and hydrophobicity of ordinary Portland cement (OPC) and alkali-activated fly ash–slag (AAFS) pastes incorporating alkyl silanes of varying alkyl chain lengths, i.e., methyl-(C1TMS), butyl-(C4TMS), octyl-(C8TMS), and dodecyl-trimethoxysilane (C12TMS). In OPC, C1TMS reduced yield stress and plastic viscosity by 33.6% and 21.0%, respectively, and improved flowability by 27.6%, whereas C4TMS, C8TMS, and C12TMS showed the opposite effects. In contrast, the effect of alkyl silanes on rheology and flowability of AAFS was less pronounced. Silanes delayed setting of OPC and AAFS by 5.6–164.4%, with shorter alkyl chains causing greater retardation. C1TMS and C4TMS inhibited early-age heat release and decreased the 1-day compressive strength by 14.8–35.7% in OPC and 82.0–84.5% in AAFS, whereas longer-chain silanes had comparatively minor effects. The hydrophobic performance in both binder systems was strongly correlated with alkyl chain length. C8TMS exhibited the best hydrophobicity in OPC, achieving a water contact angle of 145° and a 75.7% reduction in water sorptivity, while C4TMS demonstrated the highest hydrophobicity in AAFS. This study provides fundamental guidance for the rational selection of alkyl silanes in OPC and AAFS systems, offering insights into the design of multifunctional water-resistant cementitious composites for marine structures, building facades, and other applications with waterproofing requirements. Full article

This study introduces xylitol, a natural compound, as a multifunctional additive to enhance the performance of alkali-activated slag/fly ash materials (AASFMs). A systematic investigation was conducted to elucidate xylitol’s mechanism in modifying AASFM properties, including fresh behavior, hydration kinetics, compressive strength, and autogenous shrinkage. The experimental findings demonstrated that xylitol significantly delayed early-age hydration while promoting more extensive hydration at later stages. Specifically, the initial and final setting times of AASFM pastes were extended by 640% and 370%, respectively, and paste flowability increased by 30%. At a 0.2% dosage, xylitol markedly reduced porosity and refined the microstructure of AASFMs, leading to improved mechanical properties. The 3-day and 28-day compressive strengths were enhanced by 39.8% and 39.7%, respectively, while autogenous shrinkage was suppressed by 61.4%. These results demonstrate the multifunctional potential of xylitol in AASFMs, serving as an effective retarder, plasticizer, strength enhancer, and shrinkage reducer. Notably, the refined pore structure induced by xylitol may also mitigate the risks of the alkali–silica reaction, though further durability validation is warranted. Full article

As autogenous and thermal strains are significantly high in alkali-activated pastes, it becomes necessary to investigate ways to reduce these. This research studies how the volume changes of pastes made from slag activated by alkalis can be mitigated by substituting part of the slag with limestone filler and how this impacts the properties of the material, including autogenous strains, thermal strains, heat flow, compressive strength, and workability. The first part investigates how the different substitution rates impact the compressive strength and workability. The substitution rates of 15% and 30% emerged as the most optimal with a maximal reduction in the compressive strength of 23%. Five compositions were consequently investigated in the second part of the study. Isothermal calorimetry revealed that the limestone filler was probably not entirely inert and showed the effect of dilution, which is linked to the increase in the solution-to-binder ratio when the substitution rate increases. The autogenous shrinkage decreased when substituting 15% of the slag, while higher autogenous shrinkage was obtained when 30% was substituted. In addition, its rate of development was reduced. Finally, the coefficient of thermal expansion was generally slightly reduced and delayed when slag was substituted. Full article

This study explores the synergistic potential of ladle slag (LS) and sunflower shell fly ash (SSFA) in alkali-activated binder systems, focusing on their chemical and mineralogical characteristics and the influence of SSFA addition on the mechanical performance of LS-based pastes. X-ray fluorescence and XRD analysis revealed that LS is rich in CaO and latent hydraulic phases such as γ-belite and mayenite, while SSFA is dominated by K₂O, SO₃, and KCl/K₂SO₄ phases, reflecting its biomass origin. Infrared spectroscopy and thermal analysis confirmed the presence of carbonate, hydroxide, and hydrate phases, with SSFA exhibiting more complex thermal behavior due to volatile-rich composition. When used alone, LS produced weak binders; however, a 10 wt% SSFA addition tripled compressive strength to nearly 30 MPa, indicating a significant activation effect. Further increases in SSFA content led to strength reduction, likely due to increased porosity and excess salts. Microstructural analysis showed that SSFA promotes the formation of AFm phases such as Friedel’s salt and hydrocalumite, altering hydration pathways and enhancing early strength through chemical activation and carbonation processes. The findings highlight the potential of combining LS and SSFA as a sustainable binder system, offering a waste-derived alternative for low-carbon construction materials. Full article