Search Results (55)

Because artificially cemented granular (ACG) materials employ diverse combinations of aggregates and binders—including cemented soil, low-cement-content cemented sand and gravel (LCSG), and concrete—their stress–strain responses vary widely. In LCSG, the binder dosage is typically limited to 40–80 kg/m³ and the sand–gravel skeleton is often obtained directly from on-site or nearby excavation spoil, endowing the material with a markedly lower embodied carbon footprint and strong alignment with current low-carbon, green-construction objectives. Yet, such heterogeneity makes a single material-specific constitutive model inadequate for predicting the mechanical behavior of other ACG variants, thereby constraining broader applications in dam construction and foundation reinforcement. This study systematically summarizes and analyzes the stress–strain and volumetric strain–axial strain characteristics of ACG materials under conventional triaxial conditions. Generalized hyperbolic and parabolic equations are employed to describe these two families of curves, and closed-form expressions are proposed for key mechanical indices—peak strength, elastic modulus, and shear dilation behavior. Building on generalized plasticity theory, we derive the plastic flow direction vector, loading direction vector, and plastic modulus, and develop a concise, transferable elastoplastic model suitable for the full spectrum of ACG materials. Validation against triaxial data for rock-fill materials, LCSG, and cemented coal–gangue backfill shows that the model reproduces the stress and deformation paths of each material class with high accuracy. Quantitative evaluation of the peak values indicates that the proposed constitutive model predicts peak deviatoric stress with an error of 1.36% and peak volumetric strain with an error of 3.78%. The corresponding coefficients of determination R² between the predicted and measured values are 0.997 for peak stress and 0.987 for peak volumetric strain, demonstrating the excellent engineering accuracy of the proposed model. The results provide a unified theoretical basis for deploying ACG—particularly its low-cement, locally sourced variants—in low-carbon dam construction, foundation rehabilitation, and other sustainable civil engineering projects. Full article

To address the limitations of traditional hardened concrete road surfaces in coal mine tunnels, which are prone to damage and entail high maintenance costs, this study proposes using modular concrete blocks composed of fly ash and coal gangue as an alternative to conventional materials. These blocks offer advantages including ease of construction and rapid, straightforward maintenance, while also facilitating the reuse of substantial quantities of solid waste, thereby mitigating resource wastage and environmental pollution. Initially, the mineral composition of the raw materials was analyzed, confirming that although the physical and chemical properties of Liangshui Well coal gangue are slightly inferior to those of natural crushed stone, they still meet the criteria for use as concrete aggregate. For concrete blocks incorporating 20% fly ash, the steam curing process was optimized with a recommended static curing period of 16–24 h, a temperature ramp-up rate of 20 °C/h, and a constant temperature of 50 °C maintained for 24 h to ensure optimal performance. Orthogonal experimental analysis revealed that fly ash content exerted the greatest influence on the compressive strength of concrete, followed by the additional water content, whereas the aggregate particle size had a comparatively minor effect. The optimal mix proportion was identified as 20% fly ash content, a maximum aggregate size of 20 mm, and an additional water content of 70%. Performance testing indicated that the fabricated blocks exhibited a compressive strength of 32.1 MPa and a tensile strength of 2.93 MPa, with strong resistance to hydrolysis and sulfate attack, rendering them suitable for deployment in weakly alkaline underground environments. Considering the site-specific conditions of the Liangshuijing coal mine, ANSYS 2020 was employed to simulate and analyze the mechanical behavior of the blocks under varying loads, thicknesses, and dynamic conditions. The findings suggest that hexagonal coal gangue blocks with a side length of 20 cm and a thickness of 16 cm meet the structural requirements of most underground mine tunnels, offering a reference model for cost-effective paving and efficient roadway maintenance in coal mines. Full article

In this study, a kind of sustainable ultra-high-performance concrete (UHPC) was designed by using coal gangue ceramsite (CGC) and a modified Andreasen–Andersen model. However, when CGC lightweight aggregate with high water absorption is used in UHPC with a low water–cement ratio, CGC has an adverse effect on the working performance of UHPC and may lead to the decrease of mechanical properties. This study found that a 5% silane coupling agent KH560 can make CGC hydrophobic, and cause its contact angle to increase from 0° to 111.32°. Adding 100% hydrophobic modified CGC into UHPC will significantly improve its working performance, with the highest increase of 38.51%. At the same time, the addition of 20% modified CGC can further improve the compressive strength of UHPC (28 days reached 150.1 MPa), reduce the internal porosity by 21.4%, and make the interface bond more compact. In addition, the hydration degree of UHPC has also been improved, a result caused by the cement obtaining more free water for a more complete hydration reaction. This study can provide a new scheme for solving the problem of the solid waste of coal gangue. Full article

In this study, the mechanical properties and failure characteristics of concrete with 10–20 mm recycled coarse aggregate at 0%, 25%, 50%, 75%, and 100% substitution rates were studied. In addition, the influence of coal gangue powder (CGP) on the mechanical properties of concrete was studied under the dosages of 5%, 10%, 15%, and 20%. The research results show that the peak strength of recycled concrete decreases with the increase in the replacement rate of 10–20 mm recycled coarse aggregate. When the replacement rate is 25%, the decrease in strength is the smallest. When the content of CGP increases from 0 to 20%, the peak strength of recycled concrete increases first and then decreases. When the content of CGP is 15%, the peak strength reaches the maximum value. The peak strength increases slightly. The density of pores and cracks in recycled concrete increases with the increase of 10–20 mm recycled coarse aggregate replacement rate. When the substitution rate exceeds 25%, the proportion of cracks increases by nearly 1.7 times. After adding CGP to recycled concrete, the pore density and crack ratio inside a specimen are significantly reduced. When the CGP content exceeds 15%, the crack ratio tends to be stable. When the CGP content is 15%, the crack ratio is 0.519%, which is 23.5% lower than that of the RAC-25 specimen. When the content exceeds 15%, the crack ratio tends to be stable. Full article

Using coal gangue in highway base construction provides a sustainable and high-value solid waste recycling approach. This research focused on the mechanical and durability properties of coal gangue from tunneling operations. Six experimental tests, such as unconfined compressive strength (UCS), flexural–tensile strength (FTS), etc., were carried out. The impact of aggregate gradation on coal gangue mixtures’ performance was systematically evaluated. XRD and SEM were used to explore the microstructural mechanisms in cement-stabilized coal gangue–gravel mixtures (CGM). An improved evaluation model, the Delphi–entropy weight–TOPSIS (DET) method, integrating Delphi and entropy weighting, was proposed. Together with an advanced radar chart, it evaluates eight performance criteria, including mechanical, durability, economic, and environmental aspects. The results show that increasing the coal gangue content in mixtures decreases UCS, dynamic compressive rebound modulus (DCRM), FTS, fatigue life, and drying shrinkage performance. Coarse aggregates relieve drying shrinkage, while fine ones improve long-term mechanical properties. Gradation T1~3 promotes the formation of C–S–H gel and AFt crystals, enhancing compactness. Based on the DET model’s quantitative evaluation, T1~3 was determined as the optimal mix for expressway bases, achieving a balance between mechanical performance, durability, and sustainability. Full article

Coal gangue, a fine aggregate for the preparation of shotcrete mortar, is a cost-effective approach for the resource utilization of coal gangue. This study employed a mortar setting time tester, electronic universal testing machine, water absorption tester, nitrogen adsorption–desorption instrument (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), and life cycle assessment (LCA) to investigate the effects and mechanisms of replacing natural sand with coal gangue sand (0–100%) under water-to-binder ratios of 0.4 and 0.55 on the macroscopic properties, microstructure, and environmental impact of shotcrete mortar. The results showed that the porous nature of coal gangue sand increased the porosity of shotcrete mortar and reduced its compressive strength. However, its water absorption effectively decreased the effective water-to-binder ratio, significantly shortening the initial setting time. At a water-to-binder ratio of 0.55, as the replacement ratio of coal gangue sand increased from 0% to 100%, the porosity of shotcrete mortar increased by approximately 30%, the compressive strength decreased by about 40%, and the initial setting time was shortened by 57%. When the water-to-binder ratio was reduced to 0.4 and the replacement ratio of coal gangue sand was 50%, the shotcrete mortar met the application requirements of M20 shotcrete mortar, with an initial setting time of less than 12 min and a compressive strength of over 23 MPa after 28 days of water curing. Microstructural analysis revealed that the absorbed water in coal gangue sand played an internal curing role during cement hardening, improving the compactness of the interfacial transition zone. Environmental assessment results indicated that, under the same strength conditions, the life cycle environmental impact of coal gangue sand shotcrete mortar was approximately 70% lower than that of natural sand shotcrete mortar. This study provides a theoretical basis for the efficient resource utilization of coal gangue and the preparation of low-carbon shotcrete mortar. Full article

Coal gangue (CG) has become a critical environmental challenge in China, with nearly one billion tons produced annually. To address this challenge while simultaneously supplementing soil resources during mine ecological restoration, a novel process is proposed to convert CG into CG-based artificial soil (CGAS) using a microbial treatment method. This study examined the effects of local microbial agents (LMAs), commercial microbial agents (CMAs), and fly ash (FA) on key soil properties of CGAS, such as organic matter (OM) content, humic acid (HA) content, and water-holding capacity. Additionally, the mechanisms underlying aggregate formation in CGAS were investigated. The results showed that the synergistic effect of LMAs and FA significantly enhanced the essential quality properties of CGAS. In particular, the HA content increased by 2.06 times compared with untreated CG, the proportion of water-stable macroaggregates increased to 11.46%, and the bulk density decreased by 39.71%, achieving an optimal level of 1.30 g/cm³. Analysis of phase compositions, surface functional group characterization, and microstructural examination indicated that organic binders such as HA, inorganic binders such as calcium carbonate and gypsum, and the bonding effect of spherical particles of FA played significant roles in forming a stable and healthy soil structure in CGAS. Full article

Coal gangue, representing an industrial waste with the highest annual emissions and largest cumulative stocks worldwide, urgently requires resource utilization. This article uses mixed coal gangue aggregates (spontaneous-combustion coal gangue aggregate (SCGA) and rock coal gangue aggregate (RCGA)) as the research subject. The aim is to solve the technical problem of producing high-performance concrete with gangue instead of coarse aggregate. The research investigates the impact of various strength grades (C20, C30, C40, C50) and aggregate replacement ratios (0%, 20%, 40%, 60%, 80%, 100%) on the compressive strength of concrete. It explores the mechanical behaviors and properties of concrete mixed with coal gangue and develops a predictive model for its elastic modulus. The results show that (1) as the substitution rate of aggregates increases, the elastic modulus and compressive strength of the mixed coal gangue concrete significantly decrease. When the substitution rate is 100%, the elastic modulus and compressive strength of C30 concrete decrease by 3.5% and 11.3%, respectively, and the higher the grade, the more significant the reduction. For C50 concrete, the elastic modulus and compressive strength decrease by 10% and 35%, respectively. (2) A regression equation has been formulated to delineate the relationship between the compressive strength and axial compressive strength of mixed coal gangue concrete, taking into account the mix ratio of coal gangue and the compressive strength of standard concrete. This equation elucidates the correlation between the mechanical properties of concrete with varying coal gangue mix ratios and ordinary concrete across different strength grades. (3) Based on the correlation between elastic modulus and compressive strength, a prediction model for the elastic modulus of mixed gangue concrete was established, which effectively improved its prediction accuracy. Full article

Coal gangue (CG) is one of the most frequent solid wastes in the world, and it poses a severe hazard to both human society and natural ecosystems. In light of the progressive increase in environmental awareness and the unavoidable trend of the requirements of a sustainable development plan, how to efficiently use these vast quantities of CG has become an important subject in China. Concrete aggregate, which can not only solve environmental pollution but also compensate for the scarcity of natural gravel and sand resources, is the most cost-effective and eco-friendly way to utilize CG resources in accordance with the strategic requirements of green and sustainable development. However, how to deal with the preparation of high-quality gangue aggregate needs to be targeted research; blindly using gangue for concrete may bring some safety hazards. This requires that based on the source, distribution, storage, chemical composition, mineral composition of the gangue and the problems in the utilization process, efforts are made to open up the key routes of gangue concrete utilization, and to provide theoretical guidance for the high-value and environmentally friendly utilization of the CG. This paper summarizes the CG aggregate characteristics and its impact on concrete performance, discusses the technical means to improve the performance of CG aggregate concrete, and analyzes if the current CG aggregate in the concrete application of the problem still exists, with a view to gradually realize the CG of low-energy consumption bulk utilization. The popularization and application of CG aggregate will accelerate the solution of the environmental pollution problem it brings, and can to a certain extent alleviate the current situation in that the supply of natural sand and gravel resources is insufficient to meet the demand; the sustainable development of today’s research on CG aggregate for concrete has important environmental and economic significance. Full article

Addressing the complex physicochemical properties of coal gangue from typical mining areas in Inner Mongolia, this study focuses on this area’s abundant reserves coupled with the low utilization rate and significant strength variability of ecological slope protection materials. Notably, research on the alkalization–carbonization of coal gangue remains scarce. To bridge this gap, we propose a method leveraging the moisture migration behavior of coal gangue porous media. By utilizing continuous displacement high-temperature steam carbon sequestration enhancement technology, internal moisture is gradually and precisely controlled to induce the formation of high-temperature carbonic acid gas. This process facilitates internal carbon sequestration and effectively locks in the sequestration effect. This approach enables effective loading of sulfurized CO₂ composite gases in a reversible manner, achieving passive carbon sequestration driven by moisture migration. Consequently, it enhances the negative carbon content within the aggregates while bolstering their mechanical properties. After alkalization pretreatment with various concentrations and three hours of carbon sequestration, the microhardness of the aggregate surface and transition zone were observed to have increased by 24.3% and 36.4%, respectively. Additionally, the compressive and splitting tensile strengths of coal gangue concrete rose by 4.8 MPa and 0.4 MPa, respectively, while porosity decreased by up to 3.6%, and the proportion of harmful pores dropped from 11.22% to 6.54%. A strong correlation between the proportion of harmless/low-harm pores and strength development was observed. Overall, the high-temperature carbonic acid steam displacement method with sulfurized CO₂ composite gases effectively improves the physicochemical properties of coal gangue aggregates and enhances surface activity and hydration in the interface transition zone, meeting the engineering standards for in situ ecological remediation in Inner Mongolia’s mining areas. Full article

Utilizing crushed spontaneous combustion coal gangue as a coarse aggregate in concrete preparation effectively reduces reliance on natural resources and mitigates environmental pollution; however, the suboptimal workability of spontaneous combustion coal gangue coarse aggregate concrete (SCG-CAC) limits its engineering applications. To address this issue, this study places SCGCAC at the center of a CFDST (Concrete-Filled Double-Skin Steel Tubular) stub column. Through finite element modeling validated for reliability, this study examines the structural mechanical response to axial loading, along with the effects of various parameters. The analysis encompasses parameters such as the strength of the core SCGCAC (f_c,i), the strength of the sandwiched concrete (f_c,o), the yield strength of the outer steel tube (f_y,o), the yield strength of the inner steel tube (f_y,i), the width-to-thickness ratio (B/t_o), the diameter-to-thickness ratio of the inner tube (D/t_i), and the diameter-to-width ratio of the outer tube (D/B). Results show that this structural configuration significantly enhances the core SCGCAC ultimate bearing capacity, and increases in D/t_i, f_c,i, f_c,o, f_y,i, and B/t_o all lead to an increase in the peak load. Particularly, when D/t_i increases from 28.57 to 80, the peak load increases by 42.72%. However, changes in f_y,o and D/B have no significant effect on the peak load. Full article

The large-scale, open-air storage of coal gangue often leads to oxidation and decomposition due to natural weathering, resulting in decreased strength and instability, which limits its wider application in concrete pavement. To address these issues, this paper proposed a composite consolidation treatment for weathered coal gangue (WCG), assessing its effectiveness and enhancement mechanisms through aggregate performance tests, mixture performance tests, and microscopic visualization analyses. Results indicated that the initial and post-20 dry–wet cycle crushing values of WCG were 23.96% and 47.94%, respectively, failing to meet required standards. However, applying a composite consolidation treatment using a lithium curing agent and cement paste significantly improved WCG’s robustness and stability. After 4 days of treatment, the crushing value, impact value, and Vickers hardness of WCG had reached 18.3%, 6.58%, and 113.52 kgf/mm², respectively, fully meeting the standards for aggregate filling in mini concrete pavements. Furthermore, tests demonstrated that the lithium curing agent induced the formation of hydrated calcium silicate and calcium aluminate on both the surface and interior of the WCG, enhancing its structural stability. Approximately 5–12 wt.% of the curing agent penetrates and encapsulates the WCG, strongly bonding and reinforcing its internal weak surfaces. These findings offer potential solutions and technical insights for the large-scale management of weathered coal gangue. Full article

FRP-confined gangue aggregate concrete partially filled steel tubes (CGCPFTs) can not only effectively enhance the performance of coal gangue concrete, but also fully exploit the elastic-plastic mechanical behavior of the steel tubes. However, research on theoretical models that can describe their mechanical properties is yet to be conducted. To fill this gap, theoretical models for structural design and analysis were proposed for CGCPFTs. For the analytical model, based on the available experimental data, a prediction method for the stress–strain behavior of the gangue aggregate concrete in CGCPFTs, which is confined only by FRP and partly confined by both FRP and the steel tubes, was first proposed. Additionally, the condition for the synergetic deformation of the two confined states of gangue aggregate concrete within the CGCPFT was proposed. Based on the condition, an iterative incremental process was developed which subsequently allows for the theoretical calculation of the load–displacement curve for the CGCPFT under monotonic axial compression. For the design model, by introducing the constraint contribution coefficient of the steel tube, the existing closed-loop calculation formula for the stress–strain relationship of FRP-confined concrete was revised. Furthermore, by expressing the axial and lateral stresses of the steel tube as a unified circumferential effect on the concrete, the calculation methods for the ultimate strength and strain in the closed-loop formula were redefined, thus achieving the prediction of the stress–strain behavior of CGCPFTs. The comparison with the test data obtained by the author and their team revealed that both the analysis and design models could provide accurate predictions. Full article

The massive accumulation of coal gangue not only causes a waste of resources but also brings serious environmental pollution problems. To promote the utilization of coal gangue resources, mitigate environmental pollution from coal gangue, and address the shortage of natural aggregates, this study investigates the use of coal gangue to replace coarse aggregate at a 40% replacement rate to prepare coal gangue concrete (CGC). The current research on the modification of gangue concrete by BF has been less often compared with the research on the effect of basalt fiber (BF) on the properties of ordinary concrete, so in this study, BF with different admixtures and lengths were added into CGC. Additionally, basalt fibers (BFs) of varying amounts and lengths were incorporated into CGC. The study explored the effects of BF on the tensile strength, splitting tensile strength, and flexural strength of CGC. It was found that the mechanical properties of CGC improved significantly when the BF dosage was 0.10–0.15% and the length was 18 mm. This is evidenced by an increase in the compressive strength of 3.94–5.11%, split tensile strength of 11.20–16.18%, and flexural strength of 8.23–12.97%. BF was able to refine pore space, prevent crack development, and bridge cracks in CGC. To further investigate the effect of BF on the long-term service performance of CGC, the effects of BF on the appearance, quality, and compressive strength of CGC in sulfate and freeze–thaw environments were examined. The results indicated that a BF dosage of 0.10–0.15% significantly enhanced the sulfate erosion resistance and freeze–thaw resistance of CGC. This is shown by a 36.76–46.90% reduction in the rate of loss of compressive strength of CGC under the freeze–thaw cycling and a 6.21–8.50% increase in the corrosion resistance factor of CGC under a sulfate attack. BF improved the pore structure and reduced seepage channels, thereby enhancing the durability of CGC. Full article

In this paper, steel fiber coal gangue concrete is examined for its fire resistance, high strength, and stability, aiming to achieve both green sustainability and resistance to elevated temperatures. We conducted tests on concrete specimens with varying coal gangue aggregate volume replacement rates (0%, 20%, 40%, 60%) and steel fiber volume contents (0%, 0.5%, 1.0%, 1.5%) to assess their post-high-temperature mechanical properties. These tests were performed at five temperature levels: 20 °C, 200 °C, 400 °C, 600 °C, and 800 °C. The focus was on analyzing the residual mechanical properties and constitutive relationship of the steel fiber coal gangue concrete after exposure to high temperatures. The findings indicate that as the temperature rises, the compressive strength, split tensile strength, and modulus of elasticity of the steel fiber coal gangue concrete specimens undergo varying degrees of reduction. However, the peak strain and ultimate strain increase gradually. The incorporation of steel fibers enhances the mechanical properties of the coal gangue concrete, resulting in improvements in the elastic modulus and peak strain, both before and after exposure to high temperatures. Furthermore, the established constitutive relationship for steel fiber coal gangue concrete after high temperatures, derived from calculations and validated with experimental data, provides a more accurate representation of the entire damage process under uniaxial compressive loading at elevated temperatures. Full article