Search Results (425)

Cemented tailings backfill (CTB) is widely used in mining operations due to its operational simplicity, reliable performance, and environmental benefits. However, the poor consolidation of fine tailings with ordinary Portland cement (OPC) remains a critical challenge, leading to excessive backfill costs. This study addresses the utilization of modified manganese slag (MMS) as a supplementary cementitious material (SCM) for fine tailings from an iron mine in Anhui, China. Sodium silicate (Na₂SiO₃) modification coupled with melt-water quenching was implemented to activate the pozzolanic reactivity of manganese slag (MS) through glassy structure alteration. The MMS underwent comprehensive characterization via physicochemical analysis, X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) to elucidate its physicochemical attributes, mineralogical composition, and glassy phase architecture. The unconfined compressive strength (UCS) of the CTB samples prepared with MMS, OPC, tailings, and water (T-MMS) was systematically evaluated at curing ages of 7, 28, and 60 days. The results demonstrate that MMS predominantly consists of SiO₂, Al₂O₃, CaO, and MnO, exhibiting a high specific surface area and extensive vitrification. Na₂SiO₃ modification induced depolymerization of the highly polymerized Q⁴ network into less-polymerized Q² chain structures, thereby enhancing the pozzolanic reactivity of MMS. This structural depolymerization facilitated formation of stable gel products with low calcium–silicon ratios, conferring upon the T-MMS10 sample a 60-day strength of 3.85 MPa, representing a 94.4% enhancement over the T-OPC. Scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS) analysis revealed that Na₂SiO₃ modification precipitated extensive calcium silicate hydrate (C-S-H) gel formation and pore refinement, forming a dense networked framework that superseded the porous microstructure of the control sample. Additionally, the elevated zeta potential for T-MMS10 engendered electrostatic repulsion, while the aluminosilicate gel provided imparted lubrication, collectively improving the flowability of the composite slurry exhibiting a 26.40 cm slump, which satisfies the requirements for pipeline transportation in backfill operations. Full article

To investigate the mechanism by which ground granulated blast-furnace slag (GBFS) affects the performance of steam-cured cementitious materials, this study systematically analyzes the effect of GBFS on the mechanical strength and hydration products of mortar by adjusting the GBFS content (0%, 20%, 30%, 50%), curing temperature (50 °C for 7 h, 80 °C for 7 h), and curing time (3 d, 28 d). The results show that although increasing the steam-curing temperature can improve the strength activity index of GBFS-containing mortar, higher temperatures tend to induce later-age strength retrogression in such mixtures. Steam-curing not only promotes the massive formation of calcium hydroxide with coarse crystals but also increases the initial Ca/Si ratio of calcium silicate hydrate (C–S–H) gels, which is a crucial factor contributing to the high susceptibility of steam-cured concrete to brittle fracture; however, the incorporation of GBFS can effectively mitigate this issue. Furthermore, under the steam-curing condition of 80 °C, the addition of GBFS facilitates the formation of hydrogarnet and delayed ettringite, which is unfavorable for the long-term strength development and durability improvement in concrete. Full article

Addressing the environmental challenges posed by phosphogypsum (PG) stockpiling, this study investigates the synergistic mechanisms of a dual-functional application strategy where PG serves as both cementitious binder and aggregate. Unlike previous research limited to single-mode utilization, this study focuses on the interfacial compatibility between PG-based binders and PG aggregates (PGA). Through a comparative experimental program, the mechanical performance and microstructure of different binder–aggregate combinations were evaluated. The proposed dual-functional formulation achieved a high PG incorporation rate of 38% by mass. While the compressive strength of 39.3 MPa was lower than that of the reference ordinary concrete, it comfortably surpasses the C30 strength requirement for structural applications, validating its engineering feasibility. Comparative analysis revealed that although natural stone aggregates possess higher intrinsic strength, the PG-binder/PGA system exhibits superior interfacial bonding compared to the PG-binder/stone system. Microstructural observations indicated that this synergistic interaction facilitates the formation of interwoven ettringite and C-S-H gel networks, contributing to a structurally integrated interfacial transition zone (ITZ). These findings suggest that the dual-functional strategy offers a viable pathway for developing low-carbon building materials by balancing high-volume waste utilization with mechanical compliance. Full article

To evaluate the stability of fiber-reinforced cemented foamed backfill (FCFB) in complex underground mining environments, this study investigates the synergistic effects of fiber content and modified coal gangue (MCG) under acidic and high-temperature conditions. Through a systematic analysis of hydration processes, compressive strength, and deformation characteristics, the research identifies critical mechanisms for optimizing backfill performance. Calcination of MCG at 700 °C enhances gelling activity via amorphous phase formation, while modified aluminum dross (MAD) treated at 950 °C develops dense α-Al₂O₃ and spinel phases, significantly improving chemical stability. In acidic environments, the suppression of calcium silicate hydrate (C-S-H) is offset by the development of Al³⁺-driven C-A-S-H gels. These gels adopt a tobermorite-like structure, substantially increasing acid resistance. Mechanical testing reveals that while 1% fiber reinforcement promotes nucleation and densification, a 2% concentration hinders hydration. Compressive strength at 28 days shows constrained growth due to pore inhibition, and failure modes transition from multi-crack parallel failure (3-day) to single-crack tensile-shear failure. Under acidic conditions, strain concentration in the upper sample highlights a competitive mechanism between Al³⁺ migration and fiber anchorage. Ultimately, the coordinated regulation of MCG/MAD and fiber content provides a robust solution for roof support in challenging thermo-chemical mining environments. Full article

This study investigated the effects of incorporating rice husk ash (RHA) as a partial replacement for cement on the properties of concrete. To determine the optimal replacement level, RHA was used to replace cement in varying proportions, ranging from 0% to 25% in 5% increments. The mix with 0% RHA served as the control. The properties evaluated included setting time, density, and compressive strength. The results revealed that blending RHA with cement increased the initial setting time. This was attributed to the lower calcium oxide (CaO₂) content of RHA, which slows early-age hydration reactions. Conversely, the final setting time was reduced due to the pozzolanic activity of RHA, which enhances later-stage reactions. Additionally, the inclusion of RHA resulted in a decrease in concrete density, owing to its lower specific gravity and bulk density compared to Portland cement. Despite this, RHA-modified specimens exhibited higher compressive strengths than the control specimens. This strength enhancement was linked to the formation of additional calcium–silicate–hydrate (C-S-H) gel due to the pozzolanic reaction between amorphous silica in RHA and calcium hydroxide (CaOH) from hydration reaction. The gel fills concrete voids at the microstructural level, producing a denser and more compact concrete matrix. Based on the balance between strength and durability, the optimal RHA replacement level was identified as 10%. Full article

To promote the sustainable utilization of agricultural solid waste, this study proposes a novel approach for reinforcing soft clay using a peanut ash (PA)–cement composite stabilizer. The unconfined compressive strength (UCS) of pure cement and PA–cement composite systems was tested at curing ages of 3, 7, and 28 days, while the durability of the stabilized clay was evaluated through dry–wet cycling. Given that PA is rich in pozzolanic components, its addition may influence the hydration process of cement. Therefore, hydration heat analysis was conducted to examine the early hydration behavior, and XRD and TG analyses were employed to identify the composition and quantity of hydration products. SEM observations were further used to characterize the microstructural evolution of the stabilized matrix. By integrating mechanical and microstructural analyses, the solidification mechanism of the PA–cement stabilizer was elucidated. Mechanical test results indicate that the reinforcing effect increases with the stabilizer dosage. Pure cement exhibited superior strength at 3 days; however, after 7 days, specimens incorporating 5% PA showed higher strength than those stabilized solely with cement. At 28 days, the UCS of the 15% cement + 5% PA specimen reached 3.12 MPa, 11.03% higher than that of the 20% cement specimen and comparable to the 25% cement specimen (3.15 MPa). After five dry–wet cycles, the strength reduction of the 15% cement + 5% PA specimen was 22.76%, compared to 31.31% for the 20% cement specimen, indicating improved durability. Microscopic analyses reveal that PA reduces hydration heat and does not participate in early hydration, leading to lower early strength. However, its pozzolanic reactivity contributes to secondary hydration at later stages, promoting the formation of additional C-S-H gel and ettringite. These hydration products fill the inter-lamellar pores of the clay and increase matrix density. Conversely, excessive PA content (≥10%) exerts a dilution effect, reducing the amount of hydration products and weakening the mechanical performance. Overall, the use of an appropriate PA dosage in combination with cement enhances both strength and durability while reducing cement consumption, providing an effective pathway for the high-value utilization of agricultural solid waste resources. Full article

This study prepares solid-waste-based alkali-activated material (AAM) concrete using ground granulated blast furnace slag (GGBFS), fly ash (FA), steel slag (SS), and desulfurized gypsum (DG) as primary raw materials, with Na₂SiO₃ as the activator. Taking the GGBFS content (X₁), Na₂SiO₃ content (X₂), and water-to-binder ratio (X₃) as independent variables and the 3-day, 7-day, and 28-day compressive strengths and slump as response values, it investigates the influence of each factor and their interactions, constructs a response surface prediction model, screens for the optimal mix proportion with comprehensive performance, and explores the microstructural characterization and strength formation mechanism of the AAM concrete via SEM and EDS. The results indicate the following: (1) compared with binary and ternary mixtures, the use of the quaternary solid waste mixture not only enhances strength and optimizes the microstructure but also increases the utilization rate of low-quality solid wastes; (2) the regression coefficients (R²) of the response surface models are all greater than 0.98, exhibiting good goodness of fit and rationality. Experimental validation confirms that each model shows excellent predictive capability; (3) AAM concrete exhibits comprehensively superior mechanical properties to ordinary cement, with leading early- and late-stage compressive strengths and splitting strengths, albeit with a slightly lower slump; (4) the performance synergy is prominent. Combined with microscopic analysis (highly polymerized C-S-H gels and a dense structure), the superiority of its macroscopic mechanical properties stems from the optimization of the microstructure, reflecting the intrinsic correlation of the “microscopic densification-macroscopic high strength. Full article

The integration of silica nanoparticles (NS) into cementitious composites has emerged as a promising strategy to refine the microstructure and enhance concrete performance. Beyond their chemical role in accelerating hydration and promoting additional C–S–H gel formation, silica nanoparticles act as physical fillers, reducing porosity and improving interfacial bonding within the matrix. These dual effects result in a denser and more resilient composite, whose mechanical and dynamic responses differ from those of conventional concrete. However, studies addressing the vibrational and modal behavior of nano-reinforced concretes, particularly under elastic and viscoelastic foundation conditions, remain limited. This study investigates the dynamic response of NS-reinforced concrete slabs using a refined quasi-3D plate deformation theory with five (05) unknowns. Different foundation configurations are considered to represent various soil interactions and assess structural integrity under diverse supports. The effective elastic properties of the nanocomposite are obtained through Eshelby’s homogenization model, while Hamilton’s principle is used to derive the governing equations of motion. Navier’s analytical solutions are applied to simply supported slabs. Quantitative results show that adding 30 wt% NS increases the Young’s modulus of concrete by about 26% with only ~1% change in density; for simply supported slender slabs, this results in geometry-dependent increases of up to 18% in the fundamental natural frequency. While the Winkler and Pasternak foundation parameters reduce this frequency, the damping parameter of the viscoelastic foundation enhances the dynamic response, yielding frequency increases of up to 28%, depending on slab geometry. Full article

The coal washing and processing industry generates substantial quantities of coal gangue, which exerts significant impacts on soil and groundwater environments. Activating the reactivity of inert coal gangue to achieve comprehensive utilization in the field of cementitious materials holds considerable importance. This study investigates a method that synergistically utilizes thermal activation and mechanical activation to enhance the reactivity of coal gangue. The approach aims to reduce the temperature required for thermal activation while effectively stimulating the reactive properties. Furthermore, the mechanisms underlying the thermal–mechanical synergistic activation and its hydration characteristics are thoroughly examined. Experimental results demonstrate that thermo-mechanical synergistic activation, in comparison to sole thermal activation at 950 °C, enhances reaction activity by 28.3%, improves mechanical properties by 27.4%, reduces setting time by 65 min, and significantly optimizes flow performance. The XRD, FT-IR, and TG-DTG analyses demonstrate that the interlayer hydrogen bonds of kaolinite are disrupted during the thermal activation stage, resulting in the formation of amorphous and highly reactive metakaolinite. Subsequent mechanical activation after thermal treatment significantly reduces particle size, further breaks the interlayer hydrogen bonds of kaolinite, and leads to the complete disintegration of the lattice framework. This process markedly enhances the degree of amorphization and thoroughly disrupts the long-range ordered crystalline structure of the kaolinite mineral phase in coal gangue. Concurrently, the d002 interplanar spacing of kaolinite expands by 0.155 Å, leading to an increase in reactivity. SEM-EDS analysis reveals that C-S-H gel is embedded within the mortar matrix, with a reduction in calcium hydroxide content and Ca/Si ratio, and an increase in Al/Si ratio in coal gangue mortar. This confirms that the thermo-mechanical synergistic activation introduces highly reactive Ca²⁺ and Al³⁺ from coal gangue into the secondary hydration reaction, resulting in the formation of a gel structure characterized by high stability and enhanced durability. 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

Barium slag is classified as a hazardous waste due to its high content of soluble Ba²⁺. To achieve safe disposal and high-value utilization, this study developed a novel all-solid-waste road base material by synergistically combining harmlessly treated barium slag (HTBS) with steel slag, blast furnace slag, and flue-gas-desulfurization gypsum (SWB). The primary novelty of this work lies in the dual-immobilization mechanism of barium within a multi-solid-waste cementitious system. Our results showed that the mixture containing 16% binder achieved unconfined compressive strengths of 4.24 MPa (7 days) and 8.06 MPa (28 days), meeting the technical requirements for heavy-load road bases. Microstructural analyses revealed that the system evolved into a dense network composed of C–S–H gels and ettringite (AFt). Mechanistically, environmental safety is ensured by two pathways: (1) the chemical precipitation of stable BaSO₄ and (2) the physical encapsulation of ions by the dense gel matrix. Leaching tests confirmed that Ba concentration remained far below the regulatory limit, ensuring environmental safety. This work provides a scalable, eco-friendly solution for the “waste-to-resource” conversion of hazardous barium slag in road engineering. Full article

The comprehensive utilisation of solid waste is a primary approach to enhancing the utilisation efficiency of mineral resources. However, vanadium-titanium slag has long faced insufficient resource utilisation due to its low activity. To address this issue, this study integrated macro and micro analytical methods to systematically investigate the effect of mechanical grinding on the activity of vanadium-titanium slag, as well as its performance when partially replacing blast furnace slag in the system of slag—converter steel slag-desulfurization gypsum ternary gel system. Additionally, the hydration mechanism of this cementitious system was analysed. The research results indicate that mechanical grinding can significantly improve the activity index of vanadium-titanium slag and increase its specific surface area. Replacing an appropriate amount of slag with vanadium-titanium slag in the slag-steel slag-desulfurization gypsum ternary gel system can effectively enhance the mechanical properties of the cementitious system. The optimal mix proportion of vanadium-titanium slag:slag:steel slag:desulfurization gypsum as 10.5:31.5:42:16 with a water-to-binder ratio of 0.32, under which the 28-day compressive strength of the specimen reached 33.50 MPa. Through multiple microscopic analysis techniques, it was found that in the alkaline environment and sulfate excitation (provided by steel slag hydration and desulfurization gypsum), the cementitious system generates hydration products such as ettringite (AFt), C–S–H, and C–A–S–H gels. Some unreacted vanadium-titanium slag particles are wrapped and intertwined by hydrated calcium silicate (aluminium) gels, forming a stable dendritic structure that provides support for the system’s strength development. 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

Semi-Flexible Pavement (SFP) combines the flexibility of asphalt concrete and the rigidity of cement concrete to provide excellent high-temperature rutting resistance in the summer. However, its application is often limited by the fluidity and mechanical properties of cement-based grouting materials. This study systematically optimized the mix ratios of three types of grouting materials (cement-based, mineral-modified, and polymer-enhanced) using response surface methodology combined with orthogonal tests. The effects of water–binder ratio (W/B), sand–binder ratio (S/B), mineral admixtures and polymer additives on the key properties of grouting materials were systematically studied. By using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD), the evolution of the mixture microstructure and the mechanism of performance change were also analyzed. The test results show that the optimal mix ratio of the cement-based grouting material is W/B = 0.46 and S/B = 0.15; the optimal mix ratio of the mineral grouting material is to replace part of the cement with fly ash (9%), silica fume (6%) and microspheres (3%). Microscopic tests show that fly ash effectively inhibits bleeding; silica fume and fly ash promote the formation of calcium silicate hydrate (C-S-H) gel; microspheres optimize the rheology of the slurry; and the synergistic effect of silica fume and microspheres reduces the internal pores of the grouting material, achieving high fluidity, low bleeding rate and excellent mechanical properties of the grouting material. The polymer-reinforced grouting material is an enhanced slurry formed by adding high-performance water reducer (0.8%), rubber powder (2%) and coupling agent (0.9%) to the optimal mineral grouting material. The combined effect of rubber powder and coupling agent significantly improves the adhesive property between the grouting material and the asphalt interface, making it more suitable for the road performance of SFP in low-temperature environments. Full article

Phosphogypsum-based cemented paste backfill (PCPB) represents an effective solution for managing substantial accumulations of PG. However, its practical application is limited by excessive fluoride content and insufficient strength. To systematically investigate the influence of initial fluoride content on the hydration behavior, microstructures, and strength development of PCPB specimens, synthetic phosphogypsum was prepared using CaSO₄·2H₂O and NaF to eliminate impurity interference in this study. A series of specimens was designed with varying initial fluoride content (5–70 mg/L), sand-to-cement ratios (1:6, 1:8, 1:10), and concentrations (63 wt%, 65 wt%). Setting time, unconfined compressive strength, isothermal calorimetry, X-ray diffraction, and scanning electron microscopy were employed to elucidate the effects and underlying mechanisms of fluoride on PCPB performance. The results indicate that higher initial fluoride content markedly delayed setting and reduced early strength. Calorimetric analysis confirmed that fluoride postponed the exothermic peak and extended the induction period, primarily due to the formation of the CaF₂ layer on clinker particle surfaces, which hindered nucleation and hydration. The microscopic results further revealed that high fluoride content suppressed the formation of ettringite and C-S-H gels, resulting in more porous and loosely bonded microstructures. Leaching tests indicated that fluoride immobilization in PCPB specimens occurred mainly through CaF₂ precipitation, physical encapsulation, and ion exchange. These findings provide theoretical support for the fluoride thresholds in PG below which the adverse effects on cement hydration and strength development can be minimized, contributing to the sustainable goals of waste reduction, harmless disposal, and resource recovery in the phosphate industry. Full article