Search Results (3,803)

The robustness of cement slurry performance under extreme vertical temperature gradients is critical for ensuring cementing operation safety in ultra-deep wells. This study systematically investigates the interfacial behavior and hydration control mechanisms of a temperature-sensitive composite retarder, TL-2. Adsorption analysis via Total Organic Carbon (TOC) reveals that TL-2 exhibits unique non-isothermal adsorption characteristics, where its adsorption capacity slightly increases with temperature (40 °C–90 °C). This behavior overcomes the conventional limitation of drastic adsorption decline at elevated temperatures and serves as the physicochemical foundation for its wide-temperature adaptability. Performance evaluations simulated wide-temperature gradient conditions: TL-2 provided stable thickening times at 120 °C, and samples developed adequate compressive strength after 3 days of curing at lower temperatures (40 °C and 60 °C) following an initial 120 °C thickening simulation. Microstructural characterization (XRD, MIP) further elucidates the strength evolution logic across the gradient: in the lower temperature zone (40 °C–60 °C), adequate strength is established within 3 days through precise induction period control; meanwhile, at 120 °C, matrix densification is enhanced by promoting the well-crystallized tobermorite formation. The results demonstrate that TL-2 achieves a refined “buffering” effect on the liquid-to-solid transition through dynamic interfacial regulation, exhibiting superior wide-temperature adaptability across extreme thermal gradients (40 °C–120 °C) and providing essential technical support for the operational safety of ultra-deep well cementing. Full article

A low-titanium-slag-based multi-solid-waste cementitious system was developed for cemented paste backfill. The cementitious binder was prepared from low-titanium slag (LTS), steel slag (SS), municipal solid waste incineration (MSWI) fly ash, and flue gas desulfurization gypsum (FGDG), while lead–zinc tailings were used as the aggregate for backfill materials preparation. The activation of low-titanium slag, proportion optimization, and strength development mechanisms were systematically investigated. Mechanical grinding effectively activated low-titanium slag, and its activity index reached 108% after 90 min of grinding at 28 d. Steel slag alone could not fully activate low-titanium slag in the ternary system, whereas the incorporation of MSWI fly ash significantly enhanced the synergistic activation effect. The quaternary system with 40% MSWI fly ash replacement showed higher cumulative heat release and better later-age strength. The optimum backfill proportion was a solid mass concentration of 81% with a binder-to-tailings ratio of 1:4, yielding a 28 d compressive strength of 11.07 MPa with satisfactory flowability and setting behavior. Microstructural results indicated that the continuous formation of ettringite and gel phases promoted pore refinement and matrix densification. Moreover, the leaching concentrations of Pb, Zn, Cr, and soluble Cl were all below the relevant groundwater quality limits. These results demonstrate a feasible route for the high-value co-utilization of low-titanium slag and MSWI fly ash in cemented backfill materials. Full article

The growing demand for sustainable construction has highlighted the need to effectively utilize solid waste materials in concrete production, yet achieving satisfactory workability, strength, and durability simultaneously remains challenging. A multi-parameter mix-design methodology is proposed for solid-waste-based self-compacting concrete (SCC). This method couples minimum water demand, control of paste film thickness, and multi-performance balancing. The ternary solid-waste powder system (silica fume, fly ash, and supersulfated solid-waste-based cement) was first optimized through minimizing water demand to achieve maximum packing density. The resulting composition was then blended with varying dosages of ordinary Portland cement (OPC) to form the final cementitious binder. Aggregate gradation was proportioned to minimize voids, and paste volume was determined using an equivalent-paste-film-thickness model. Under comparable mixture conditions, SCC with OPC contents of 70–40 wt.% and paste film thicknesses of 2.0–2.6 mm was evaluated for fresh performance, compressive strength, freeze–thaw resistance, and material cost. Mixtures with a paste film thickness of 2.4 or 2.6 mm satisfied the self-compactability criterion—the mix with 50 wt.% OPC and a paste film thickness of 2.4 mm showed the best overall performance balance, achieving higher 28 d strength than higher-OPC mixtures while improving freeze–thaw resistance and reducing cost. Results from TGA, XRD, ATR–FTIR, and SEM–EDS analyses indicated enhanced calcium hydroxide (CH) consumption, increased formation of C-(A)-S-H and ettringite, and a denser interfacial transition zone (ITZ), supporting the proposed multi-objective design approach. While the framework was validated for a specific ternary binder system, it provides a reproducible proportioning strategy applicable to a broader range of solid-waste-based concrete systems, with potential for extension to other waste streams and exposure conditions, thus supporting the development of more resource-efficient and environmentally sustainable concrete. Full article

As solid waste generated from shield tunnel construction, shield muck is characterized by its massive volume, high water content, and poor engineering properties. Large-scale stockpiling not only occupies precious land resources but also poses potential environmental risks. This has become one of the key bottlenecks hindering the green, low-carbon, and sustainable development of rail transit construction. Efficient dewatering is a key prerequisite for its subsequent disposal or reutilization. Lime, cement, phosphogypsum, nano-SiO₂, and ground granulated blast furnace slag were employed in this research as composite conditioning agents to dewater shield tunnel muck. A range of water content, pH, and total organic carbon analyses tests were conducted to explore the roles of lime, cement, phosphogypsum, nano-SiO₂, and ground granulated blast furnace slag on the dewatering effect of shield tunnel muck. Furthermore, microstructures and elemental distribution of typical mixes were analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy tests. Results indicate that a composite agent consisting of 3.5% lime, 4% cement, 1% phosphogypsum, 0.2% nano-SiO₂, and 4% ground granulated blast furnace slag exhibits optimal performance, reducing water content from 50% to 29.8% within 24 h. Phosphogypsum significantly decreased pH and reduced TOC to below 1 g/kg after 15 days, effectively mitigating the environmental hazards associated with muck disposal. The formation of cementitious products, including calcium aluminate hydrate, calcium aluminosilicate hydrate gels, and calcium silicate hydrate, effectively bonds soil particles. Additionally, ettringite crystals produced by the reaction between phosphogypsum and calcium aluminate phases filled interparticle voids. These processes were identified as the primary mechanisms for water reduction. Although nano-SiO₂ exerted a limited direct influence on water content, it acted as a pozzolanic catalyst that accelerated hydration reactions of lime and cement, rapidly reducing muck fluidity. The synergistic effect of the composite dewatering agent components establishes a multi-mechanism dewatering system characterized by “hydration gel + AFt filling + nano-catalysis.” The dewatering system developed in this study achieves both high efficiency and environmental friendliness for shield tunnel muck. This provides technical support for subsequent resource utilization, such as subgrade filling, while promoting the recycling of industrial solid wastes like phosphogypsum and blast furnace slag, ultimately contributing to green, low-carbon, and sustainable development. Full article

Alkali-activated cementitious materials (AACMs) are recognized as promising green building materials and a viable alternative to traditional cement due to their low carbon footprint, high durability, and superior mechanical properties. These materials primarily utilize industrial by-products such as coal gangue, steel slag, and gasification slag. The alkali activation process offers an environmentally friendly pathway for the construction industry. To address the need for the large-scale utilization of bulk solid wastes, this study established a ternary solid waste synergy system comprising coal gangue, steel slag, and gasification slag. The preparation and performance optimization of AACMs based on this system were investigated. An optimal mix proportion was identified through orthogonal experiments, and the influence of various factors on the mechanical properties at different curing ages was analyzed. The results indicate that the fluidity of all AACMs meets the requirements for general backfilling applications. Among the alkali activators, Na₂SO₄ had the smallest effect on fluidity. Under single-activator conditions, sodium silicate (water glass) and sodium hydroxide exerted a greater influence on strength development compared to anhydrous sodium sulfate. For the composite activator system, the significance of parameters affecting compressive strength followed the order: silicate modulus > alkali activator content. The maximum 28-day unconfined compressive strength reached 7.653 MPa with a mix proportion of 55% coal gangue, 45% steel slag, and 5% gasification slag, as well as a silicate modulus of 1.2 and a water glass content of 8%. This represents increases of 540.95% and 299.25% compared to the non-activated group and single-activator groups, respectively. Microstructural analysis revealed that the enhanced integrity and strength of AACMs are attributed to pore-filling by hydration products, predominantly C–S–H and C–A–S–H gels. This study successfully developed high-performance AACMs based on a coal gangue–steel slag–gasification slag ternary system, elucidating the critical regulatory role of silicate modulus in composite activators and the underlying microstructural strengthening mechanisms. The findings provide a theoretical foundation and technical support for the high-value, large-scale utilization of bulk industrial solid wastes in building materials. Full article

The cement plug-casing interface is critical for long-term wellbore integrity in well abandonment to prevent fluid channeling. However, traditional cement easily debonds under long-term in situ stress and fluid exposure, causing seal failure and safety risks. To address this issue and overcome the limitations of conventional cement, a three-dimensional finite element model was established based on stress-seepage coupling theory. A systematic comparative analysis of the interface debonding mechanisms for three materials—cement, resin, and alloy—and their different combination sequences was conducted. The entire process of interface damage was quantified. The effects of material combination, formation elastic modulus, and injection rate on sealing performance were analyzed. Results show that the stiffness gradient dominates the failure mode, and the “cement–resin–alloy” configuration best suppresses damage propagation, reducing failure height by about 30%. Additionally, interface integrity is sensitive to formation constraints and operational parameters: the interface failure height decreases as the formation elastic modulus increases, and increases as the injection rate rises. The findings of this study can provide a theoretical basis and engineering reference for the optimal design of composite plugging barriers in demanding operational conditions, such as those encountered in carbon sequestration wells. Full article

The dielectric properties of cement-based composites (CBC) are highly sensitive to environmental humidity, which seriously restricts the quantitative interpretation accuracy of ground-penetrating radar (GPR) in the non-destructive testing of cement concrete pavement. In view of the lack of targeted prediction models due to the unclear mechanism of humidity influence in existing research, the core innovations of this study are: (1) the synergistic mechanism of water vapor dipole polarization and adsorbed water multi-layer polarization is clarified, revealing the intrinsic reason for the accelerated growth of permittivity in the high humidity range; (2) the constructed four-component dielectric model of “cement mortar–aggregate–water vapor–adsorbed water” achieves high-precision prediction within the range of 50~100% RH (R² > 0.94, relative error < 5%), and shows good predictive ability within the test scope of this study; (3) a GPR humidity correction protocol based on the model is proposed, which can effectively improve the accuracy of nondestructive testing of cement concrete structures. In this study, CBC samples with water–cement ratios of 0.4~0.6 were prepared using P.O 32.5/P.O 42.5 cement and limestone aggregate. Under the conditions of 20 ± 0.5 °C, relative humidity (RH) of 50~100%, and 2 GHz (common GPR frequency), the permittivity was measured using an Agilent P5001A network analyzer to verify the model. The results show that the permittivity increases monotonically with humidity, and the growth rate in the high humidity range (70~100%) is 2.2 times that of the low humidity range (50~70%); The higher the water–cement ratio, the shorter the age, and the lower the cement strength grade, the stronger the humidity sensitivity of CBC dielectric properties. This model provides a reliable humidity correction tool for GPR detection, and significantly improves the accuracy of nondestructive evaluation of cement concrete structures. Full article

This study investigates the influence of bottom ash (BA) and marble dust powder (MD) as partial replacements for Ordinary Portland Cement (OPC) on the physical, mechanical, and mass loss performance of cement pastes under cyclic seawater exposure and their economic feasibility. Mixtures containing 0–20% BA and 0–20% MP were tested to evaluate their workability, strength, porosity, durability, and cost efficiency. The results indicate that BA reduces workability, which is reflected in the lower slump values of mixtures with a higher BA content, whereas MD enhances fluidity by filling the voids between particles and improving the packing density of the mixture, which results in better workability. The optimal composition, which was 15% bottom ash and 10% marble dust powder, achieved a superior mechanical performance, with compressive strength (CS) and flexural strength (FS) increases of 2.2% and 38.7%, respectively, at 28 days compared to the control. Increasing the BA and MD content up to a total of 35% of the binder generally led to a moderate reduction in early-age strength, while mixtures with 20% replacement exhibited comparable or improved long-term strength at 90 days. This led to decreased porosity and improved long-term mass loss performance under cyclic seawater exposure. The incorporation of BA and MD also reduced water absorption, indicating enhanced durability, with these beneficial effects becoming more pronounced at later ages. Economically, cement substitution with BA and MD reduced production costs by up to 39.6%. In summary, moderate incorporation of BA and MD enhances performance, reduces cost, and supports the sustainable utilization of industrial waste in cementitious materials. The mixture proportions investigated in this study offer a promising alternative binder for use in the sustainable building sector. Full article

Foam concrete and fiber-reinforced foam concrete are promising building materials for sustainable and energy-efficient construction. Improving the environmental performance of cellular composites through the use of industrial waste and additives based on them is highly relevant. This study intends to create a novel complex nanomodifying additive (CNA) from industrial waste and nanomaterials, alongside new eco-friendly foam concrete (FC) and fiber-reinforced foam concrete (FFC) mixes incorporating CNA and polypropylene fiber (PF). Experimental studies yielded the optimal CNA formulation and described a method for its preparation. The test results indicate that FC’s properties are enhanced by CNA. The properties were best in the FC that was modified with 10% CNA. The FC control composition was surpassed by a 25.5% increase in compressive strength and a 23.1% increase in flexural strength, with a 9.5% reduction in thermal conductivity. Dispersed PF reinforcement also positively impacts the properties of FFCs with CNA, and the combined modification of 10% CNA and 1.2% PF provides maximum increases in compressive and flexural strength, amounting to 43.1% and 102.2%, respectively, and a 16.9% reduction in thermal conductivity. A microstructural analysis of the cellular composites confirms the feasibility of the tested formulation solutions. The FFCs, when modified by CNA and PF, display a homogeneous cellular structure, and the interpore zones contain multiple clusters of calcium silicate hydrate. Using CNA in the production of FC and FFCs will reduce cement consumption and improve their environmental friendliness. Full article

Coal gangue (CG), a bulk solid waste produced during coal mining, is rich in active components such as silicon and aluminum oxides, making it a high-quality raw material for the production of cementitious materials. Its utilization represents a significant pathway for achieving high-value applications of CG and facilitating the low-carbon transformation of the cement industry. Owing to advantages such as low carbon emissions, environmental friendliness, cost-effectiveness, and tunable performance, CG-based cementitious materials have been extensively investigated by researchers worldwide. Studies have focused on various aspects, including cementitious backfill materials, CG solid waste-based cement, geopolymers, concrete, and composite materials derived from CG. This paper systematically reviews the regional distribution, mineral composition, chemical constituents, and reactivity characteristics of CG. It further summarizes recent advances in activation techniques, performance optimization, and engineering applications of CG-based cementitious materials. Current challenges, such as insufficient activation efficiency, ambiguous hydration mechanisms, and limitations in large-scale application, are critically analyzed. Finally, future research directions and development trends are outlined to provide a theoretical foundation for further investigation and industrial implementation of CG-based cementitious materials. Full article

This study investigates the development of a composite material based on agricultural plant waste from Kazakhstan, utilizing a multicomponent binder incorporated with rice husk ash. The implementation of low-clinker binders enables the full utilization of ash dumps from the Kyzylorda thermal power plant (TPP) and rice husk residues from local rice-processing enterprises. Physical and chemical analysis of the ash–cement stone revealed a reduction in portlandite content compared to control samples. Phase composition analysis indicated the presence of hydroaluminate C₄AH₁₃ and a reduction in calcite, suggesting accelerated crystallization of calcium silicate hydrates. The formation of crystalline phases and intergrowth structures is assumed to contribute to the strengthening of the gel-like matrix. Experimental optimization of the ash–cement binder with rice husk ash yielded compressive strengths ranging from 3.03 to 4.10 MPa at densities of 790–900 kg/m³, depending on the type of organic filler. These results confirm the feasibility of using locally sourced agricultural waste for the production of heat-insulating and structurally stable composite materials. Full article

Fiber-reinforced cemented tailings backfill (FTB) has been widely adopted in underground mining operations as an effective solution for mitigating the brittleness of cemented tailings backfill (CTB) and ensuring compatibility with deep mining environments. Understanding the coupled effects of temperature and binder composition on the thermal–hydro–mechanical–chemical (THMC) behavior of FTB is essential for low-carbon mix design and practical application. To address this knowledge gap, this work presents a systematic investigation into the influences of curing temperature, binder type, and cement content on the rheological properties, compressive strength, and THMC-related parameters of FTB. The results demonstrate that elevated temperatures accelerate hydration, reducing flowability while significantly enhancing strength and pore structure refinement. Conversely, low temperatures preserve flowability but impede strength development. The incorporation of slag or fly ash as partial cement substitutes reduces rheological parameters; however, fly ash substitution tends to compromise ultimate strength. Multi-field performance monitoring further reveals the underlying coupling mechanisms among temperature evolution, hydration kinetics, matric suction, and mechanical strength development. Based on these insights, a low-carbon design strategy is proposed, emphasizing dynamic optimization of cement content according to ambient temperature. These findings offer a theoretical foundation for the sustainable proportioning and performance control of mine backfill materials. Full article

To develop a high-performance inorganic fireproof coating suitable for steel structures, this study utilized magnesium phosphate cement (MPC) as the matrix and introduced expanded perlite (EP) as a lightweight aggregate. The effects of EP content (40–55%) and magnesium-to-phosphorus ratio (M/P = 4:1–7:1) on the dry density, compressive strength, bond strength, and fire resistance of the coating were systematically investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) were employed to reveal the phase evolution and microstructure evolution mechanisms at high temperatures. The results indicate that increasing EP content significantly reduces the dry density and thermal conductivity of the coating, enhancing thermal insulation performance. However, excessive incorporation leads to the deterioration of mechanical properties, with an optimal EP content of 45%. The M/P ratio influences the interfacial bond strength and high-temperature structural stability by regulating the proportion of the hydration product K-struvite (KMgPO₄·6H₂O) and residual MgO. Compressive strength peaked at M/P = 6:1 (0.80 MPa), while bond strength was optimal at M/P = 5:1 (0.097 MPa), corresponding to the best fire resistance (back-side temperature of 180.4 °C). At high temperatures, K-struvite dehydrates and transforms into anhydrous KMgPO₄, which, together with residual MgO and crystallized SiO₂ from EP, forms a dense ceramic skeleton, ensuring the structural integrity of the coating. Comprehensive performance evaluation determined the optimal mix ratio as M/P = 5:1 and EP content = 45%. The coating with this ratio exhibits a dry density of approximately 560 kg/m³, a 14-day compressive strength of 0.53 MPa, a bond strength of 0.097 MPa, and a back-side temperature of 180.4 °C under flame exposure, demonstrating a favorable balance of lightweight character, mechanical integrity, and thermal insulation performance suitable for steel structure fire protection applications. Full article

This study examines the utilisation of fly ash from the energy sector as a secondary raw material in cement composites, with the aim of improving sustainability while maintaining high mechanical performance. By partially replacing Portland cement with industrial by-products, the proposed approach supports resource efficiency and aligns cement composite production with circular economy principles. Three formulations were tested: a reference mix and mixes with 25% and 50% cement reduction. Compressive strength reached 41 MPa, confirming suitability for construction use. Chemical and textural properties were analysed using XRD, FTIR, TGA, and nitrogen adsorption (BET, BJH). The results showed structural modifications, including new crystalline phases and changes in porosity. XRD confirmed newly formed phases, while FTIR identified Si-O-Si and Al-O-Si bonds, indicating effective activation of fly ash. Reducing cement content increased surface area and mesoporosity, enhancing performance. The findings demonstrate that fly ash can serve as a sustainable substitute for Portland cement within a circular economy framework, supporting CO₂ emission reduction and resource conservation while enabling the production of durable and environmentally responsible cement composites. Full article

Calcium–silicate–hydrate (C-S-H), the primary binding phase governing cement paste cohesion, undergoes progressive physicochemical transformation upon carbonation—a process that critically dictates concrete durability in atmospheric environments. When CO₂ penetrates the porous cement matrix, it triggers a cascade of degradation mechanisms: calcium leaching decalcifies the C-S-H structure, inducing polymerization of silicate chains from dimeric to longer-chain configurations, while concurrent precipitation of calcium carbonate and amorphous silica gel fundamentally reconstitutes the nanoscale architecture. These nanoscale alterations propagate to macroscopic property evolution, manifesting as initial strength and stiffness gains due to pore-filling carbonation products followed by eventual deterioration as the cohesive binding network deteriorates. This review synthesizes current understanding of carbonation-induced structural evolution, examining the coupled influences of environmental parameters—CO₂ concentration, relative humidity, and temperature—alongside C-S-H intrinsic chemistry (Ca/Si ratio, aluminum substitution, and alkali content) on reaction kinetics and material performance. However, significant knowledge gaps persist: predictive models for in-service carbonation rates remain elusive due to the disconnect between idealized laboratory conditions and the heterogeneous, cracked reality of field concrete; the causal linkage between nanoscale C-S-H alteration and macroscale cracking patterns along with physical performance is poorly resolved, and most mechanistic studies rely on synthetic C-S-H, neglecting the compositional complexity of real Portland cement systems. We further propose emerging protection strategies, including surface barrier coatings and low-carbon alternative binders (geopolymers, calcium sulfoaluminate cements, carbon-negative materials such as recycled cement), which demonstrate enhanced carbonation resistance. Future research priorities include developing effective coating barriers for carbonation protection, developing operando characterization techniques for real-time reaction monitoring, deploying machine learning algorithms to bridge atomistic simulations with structural-scale predictions, and establishing long-term field performance databases to validate laboratory-derived degradation models. Full article