Search Results (156)

The particle size and dosage of quartz sand significantly affect the bleeding and segregation of UHPC mixtures, thereby influencing their strength and durability. However, the maximum particle size of quartz sand is a key focus of existing research, and the influence sensitivity of particle size gradation and dosage for UHPC performance are not clear. Based on this, this study systematically investigates the effects of particle size gradation and dosage of quartz sand on the slump flow and strength of UHPC, and the grey relational analysis method is employed to identify the sensitive particle size fractions. The results show that the compressive and flexural strength of UHPC with quartz sand mixing ratio of 40:40:20 and 40:50:10 is significantly improved at both 7 d and 28 d curing ages compared with those using coarse, medium, and fine quartz sand individually. The order of particle size affecting slump flow, flexural and compressive strength of UHPC is 0.6–1.18 mm > 0.3–0.6 mm > 1.18–2.36 mm > 0–0.075 mm > 0.075–0.15 mm > 0.15–0.3 mm. The key measure for enhancing strength and ensuring workability of UHPC lies in the proportion of quartz sand with particle size of 0.6–1.18 mm, which needs to be above 40% to serve a filler and framework function. When coarse, medium, and fine quartz sand mixing ratio equals to 40:40:20, the dosage increases lead to the decrease in UHPC slump flow, and as the quartz sand dosage varies from 900 kg/m³ to 1500 kg/m³, the 28 d compressive strength of UHPC first increases and then decreases. It is recommended to use a quartz sand dosage of 1050 kg/m³ ± 50 kg/m³ and mixing ratio of 0.6–1.18 mm quartz sand larger than 40% to produce UHPC exhibiting slump flow larger than 600 mm and compressive strength of 120–150 MPa. The findings provide important guidance for the preparation and performance regulation of UHPC. Full article

To explore the fracture performance and crack propagation mechanism of basalt fiber (BF)-reinforced asphalt mixtures and overcome the limitations of single-factor performance evaluations, this study systematically investigates the effects of aggregate gradation, material scale and test conditions on fracture behavior. The semi-circular bending (SCB) test was integrated with digital image correlation (DIC) technology to synchronously obtain macroscopic fracture parameters and full-field displacement/strain fields. The findings showed that fine aggregate particle size could better utilize the bridging effect of BFs, increasing fracture energy by 25.8% versus 15.9% for the coarse aggregate particle size. A consistent enhancement in fracture performance is observed between the asphalt mixture and the asphalt mortar after BF incorporation. Under the same test conditions, the addition of fibers increased the fracture energy by 25.8% for the mixture and by 28.4% for the mortar, while fracture toughness increased by 6.9% and 8.3%, respectively. The lower loading rate reduces the reinforcement effect due to viscoelastic stress relaxation, while low temperatures enhance the relative crack resistance efficiency of BFs. The incorporation of fibers increases the crack tortuosity coefficient by a range of 4–14%, leading to greater energy dissipation. However, low temperatures absolutely dominate the crack morphology. This study provides an experimental reference for the differentiated design of BF-reinforced asphalt mixtures under different gradation types and climatic conditions. Full article

The stability of tailings dams is governed predominantly by the physical properties and geotechnical behavior of their primary construction material—tailings. Consequently, a systematic understanding of these characteristics is of great significance for the rational design and long-term stable operation of tailings dams. This review focuses on the physical properties and geotechnical behavior observed in different types of tailings. In terms of physical properties, the particle size distribution exhibits a pronounced hydraulic classification characteristic within the impoundment, consisting predominantly of silt-sized particles and displaying an overall trend toward finer gradation. The mineralogical and chemical composition is dominated by quartz, hematite, and silicates. However, significant spatial variability exists both between different tailings types and across distinct zones within the same tailings pond. Regarding geotechnical behavior, the permeability of tailings is governed by a fines content threshold: below this threshold, permeability decreases with increasing fines content, while beyond it, the permeability stabilizes. When studying consolidation and compression behavior using slurry specimens, the compression curves exhibit nonlinear characteristics, primarily described by the modified Gibson theory. The shear behavior of tailings is significantly influenced by confining pressure, drainage conditions, anisotropy and stress paths. The presence of transitional behavior leads to the critical state line determined based on a single sampling method erroneously assessing the dilation/cosntraction characteristics of in situ tailings, thereby affecting the assessment of liquefaction risk. Future research should focus on the seepage, consolidation and shear properties of clayey fine-grained tailings and unsaturated tailings, and aim to elucidate the key controlling factors of transitional behavior to enhance the reliability of tailings dam stability assessments. Full article

The fracture of bituminous polymer composites is fundamentally dictated by microstructural heterogeneity and the complex viscoelasticity of the asphalt matrix. This study develops a robust numerical framework coupling a random polygonal aggregate distribution algorithm with a bilinear cohesive zone model (CZM) to simulate fracture mechanics in heterogeneous asphalt-based composites. A key feature of the model is the explicit accounting for the stochastic distribution of the coarse aggregate and the time-dependent mechanical response of the fine aggregate matrix (FAM). Following experimental validation via frequency sweep and semi-circular bending (SCB) tests, a multi-scale parametric analysis was conducted to quantify the impacts of aggregate gradation, volume fraction, and shape. Results demonstrate that mixtures with high percentages of large-sized aggregates effectively delay macroscopic fracture by increasing the energy dissipation required for cracks to bypass the aggregate phase. While increasing the volume fraction of aggregates improves peak strength, it simultaneously accelerates post-peak load deterioration and reduces total fracture work, indicating a critical loss in the composite’s deformation capacity. Furthermore, particles with higher angularity provide superior blocking effects compared to rounded counterparts. This research offers a high-efficiency computational tool for the structural optimization of highly filled composites and provides critical insights into their internal stress states and macroscopic fracture mechanics. Full article

To enhance the engineering performance of fine-grained composite soils with unbalanced particle gradation, high plasticity, and poor water stability, a synergistic stabilization strategy combining particle structure regulation and microbially induced calcium carbonate precipitation (MICP) was proposed. The particle size distribution and fundamental engineering properties of a titanium gypsum–clay (TSC) composite soil were first optimized through systematic single-factor blending tests. The results indicate that a TS:C ratio of 60:40 significantly improved gradation characteristics, reduced plasticity, and enhanced both compaction behavior and load-bearing capacity. Based on the optimized gradation framework, MICP treatment was subsequently introduced to further enhance water stability. The effects of key parameters, particularly the type of calcium source, on the evolution of water stability were systematically investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to elucidate the underlying reinforcement mechanisms. The results demonstrate that the water stability coefficient increased markedly from 0.35 to 0.83 following MICP treatment, while strength degradation under water immersion was effectively mitigated. Microscopic observations reveal that microbially precipitated calcite fills pore spaces and forms a continuous cementation network via particle bridging and interfacial bonding, leading to an approximately 32% reduction in porosity. Overall, the proposed synergistic strategy offers an effective and sustainable approach for improving the water stability and structural integrity of complex fine-grained composite soils. Full article

The nominal maximum aggregate size (NMAS) plays a critical role in determining the mechanical performance of cement-stabilized macadam (CSM), yet its meso-mechanical influence mechanism remains insufficiently understood. In this study, three skeleton-dense CSM mixtures with different NMAS values were designed, and a combined experimental–numerical approach was adopted to investigate the macro- and meso-scale mechanical behavior. Uniaxial compression tests and aggregate crushing value tests were conducted to evaluate strength development and load-transfer characteristics, while a three-dimensional discrete element method (DEM) model incorporating realistic aggregate morphology was established to analyze the evolution of contact forces and crack propagation. The results show that increasing NMAS significantly improves the mechanical performance of CSM. Compared with CSM-30, the 7-day compressive strength of CSM-40 and CSM-50 increased by approximately 10.3% and 37.3%, respectively. The stress–strain response indicates that mixtures with larger NMAS exhibit higher stiffness and a higher strain. At the meso-scale, a larger NMAS promotes the formation of a more efficient force-chain network dominated by coarse aggregates. Strong contacts were predominantly carried by aggregates larger than 9.5 mm, and in CSM-50, the proportion of strong contacts in the 37.5–53 mm fraction exceeded 90%, indicating that the largest particles likely form the primary load-bearing skeleton. In addition, increasing NMAS delayed crack initiation, reduced crack propagation rate, and decreased the total number of cracks at failure. These findings demonstrate that macroscopic strength improvement is closely associated with meso-scale optimization of the aggregate skeleton and enhanced load-transfer efficiency. This study provides a mechanistic basis for NMAS selection and gradation optimization in semi-rigid base materials. Full article

The particle size of aggregate is a key factor affecting the mechanical properties and deformation capacity of cemented gangue filling body. In this study, coal gangue with a particle size range of (0.05, 20) mm was sieved into six groups of aggregate particles. Based on the Talbot gradation theory, cubic specimens with gradation indices n = 0.3, 0.4, 0.5, 0.6, and 0.7 were prepared for acoustic emission (AE) monitoring tests. The microstructure of the filling body was analyzed, and the failure characteristics and damage evolution laws of the cemented gangue filling body with different gradation indices were explored. The results show that the compressive strength reaches its maximum when n = 0.5. As the gradation index increases, the compressive strength of the specimens first increases and then decreases, and the specimens shift from primarily experiencing cleavage failure to shear failure. The curve of cumulative AE ringing count shows a bimodal distribution pattern, with both surge points and fracture points coexisting. The surge points can be regarded as precursor signals of backfill failure. The spatiotemporal evolution of AE events exhibits complex phased changes. An excessively small gradation index tends to form micropores and striped microcracks, reducing the compactness of the microstructure. An excessively large gradation index can lead to the formation of penetrative weak channels. A reasonable gradation index enables the mutual interlocking of aggregate particles, constructing a stable three-dimensional spatial skeleton structure. The dynamic trend of damage in the filling body can be captured based on AE analysis, and reverse guidance can be provided for parameter optimization of Talbot gradation, achieving a dynamic closed loop of “gradation design-AE monitoring-damage assessment-parameter optimization”. This not only enriches the application scenarios of acoustic emission analysis in graded materials, but also provides a new research approach and technical method for gradation design and safety assessment in scenarios where particle sizes are missing in practical engineering. Full article

Against the backdrop of dual-carbon goals and resource constraints, the high-value utilization of recycled fine aggregates (RFAs) remains limited, leading to inconsistent engineering performance and insufficient durability. Enzyme-induced carbonate precipitation (EICP) represents a promising low-carbon cementation method, yet its deposition uniformity and cementation efficiency are influenced by the pore structure of granular media and associated mass transfer pathways. This study employs a two-stage experimental design to investigate the synergistic effects of particle size distribution characteristics, represented primarily by d₅₀, and fiber addition on EICP-cemented RFA. Phase I (fiber-free; d₅₀ = 0.67–1.14 mm) results indicate that, across the tested gradation schemes, the CaCO₃ content generally decreased from 9.49% to 7.72% as the representative d₅₀ increased, while the dry density changed only slightly (1.637–1.617 g/cm³). However, the unconfined compressive strength (UCS) decreased from 1000 kPa to 541 kPa (45.9% reduction), indicating that strength is primarily governed by the connectivity of the cementation network rather than solely by the degree of densification. In Phase II, glass fiber (GF), polypropylene fiber (PPF), and jute fiber (JF) were incorporated into the ERFA4 gradation scheme selected for fiber modification. All three systems exhibited a unimodal optimum pattern: the peak CaCO₃ contents reached 10.71% (GF 0.5%), 10.11% (PPF 0.7%), and 11.46% (JF 0.7%), corresponding to peak UCS values of 1917, 1874, and 2450 kPa, respectively. Microscopic analysis suggested that fiber bridging coupled with CaCO₃ deposition may contribute to the formation of a “fiber-CaCO₃-particle” stress-transfer network, which is consistent with the observed enhancements in load-bearing capacity, ductility, and post-peak stability. Full article

Temperature control and crack prevention are crucial for mass concrete structures in cold regions. Electrically conductive roller-compacted concrete (ERCC) provides a promising route to shift surface temperature regulation from passive protection to active control. To develop an ERCC material suitable for engineering applications, this study first established a quantitative relationship between interparticle interaction energy and particle spacing to elucidate the effect of carbon black (CB) dispersion and agglomeration on concrete performance. The dispersion quality of CB was then evaluated by sedimentation tests, UV absorbance, and resistivity measurements. The absorbance of CB suspensions containing PCE, SDS, and TA increased by 79.9%, 80.1%, and 100.4%, respectively, compared with the suspension without dispersant, and TA gave the lowest mortar resistivity. Mechanical tests and mesoscopic simulations showed that coarse aggregate volume fraction and CB dosage had stronger effects on the compressive strength and elastic modulus of ERCC than aggregate gradation and specimen size. After calibration using the ERCC-2-TA mixture, the average errors between simulation and experiment were 0.7% for compressive strength and 0.4% for elastic modulus. For engineering applications, the recommended ERCC parameters were a coarse aggregate volume fraction of 40%, a CB content of 4–5% and a water-to-binder ratio of 0.45–0.50 for roads, and a CB content of 8% with a water-to-binder ratio of 0.55 for dams. Full article

As an effective technical approach for ecological environment protection in mining areas and coal resource recovery under buildings, railways and water bodies, solid backfill coal mining technology has been widely applied. When gangue was used as backfill material and placed into the goaf, its compression characteristics and crushing behavior were found to directly affect the control effect of overlying strata deformation. In this study, combined with the compression characteristics of gangue solid waste backfill materials, eight kinds of gangue solid waste backfill materials with different particle size gradations were adopted as research objects. From the perspectives of stress–strain compaction characteristics, the coupling relationship between internal crushing and acoustic emission (AE), relative density in the compacted state and particle size distribution, the hierarchical crushing behavior, and the AE response characteristics of gangue solid waste backfill materials under different gradation schemes were systematically revealed, and the optimal gradation parameters for different layers were determined. The results showed that the compaction process of gangue solid waste backfill materials could be divided into three stages: initial compression, rapid compaction and plastic compaction. During the compaction process, internal crushing was mainly concentrated in the middle layer. In the initial stage of the test, the AE intensity of the middle layer was measured to be higher than 78%, and the AE intensity remained above 50% in the compacted state. When the specimen was compressed to 220 mm, all eight gradation schemes exhibited the characteristic that the proportion of locating points and energy level in the middle layer were much higher than those in the upper and lower layers. With the continuous increase in axial pressure, the intensive area of crushing events was observed to migrate in the order of middle layer → upper layer → lower layer. With the continuous increase in axial pressure, the intensive area of crushing events was observed to migrate in the order of middle layer → upper layer → lower layer. The findings obtained in this study have provided a theoretical basis and experimental support for the gradation optimization of gangue solid waste backfill materials and roof deformation control in solid backfill coal mining engineering. Full article

It is of great significance to clarify the evolution law and control mechanism of fracture conductivity in different production stages for the efficient development of coalbed methane. However, research on fracture conductivity in coal–rock remains limited, and the existing models are inadequate for predicting fracture conductivity with a consideration of staged proppant crushing. To address this gap, long-term conductivity tests were conducted on deep coal–rock under varying closure pressures and proppant gradation ratios. Within a coupled computational fluid dynamics and discrete element method (CFD-DEM) framework, a particle substitution scheme was integrated with the energy-based breakage model (Tavares breakage model) to develop a fracture conductivity predictor that incorporates proppant crushing and captures the time-dependent kinetics of proppant breakage during fracture conductivity evaluation. The model’s predictions align well with the experimental data, with an average error of less than 5%. The results indicate that fracture conductivity evolution can be delineated into three stages according to particle-breakage characteristics, (i) proppant pack compaction, (ii) the primary crushing of coarse proppant grains, and (iii) the secondary crushing of proppant fines, and the contributions of these three stages to the total conductivity loss are approximately 60%, 30%, and 10%, respectively. At a low closure pressure, fracture conductivity varies markedly among proppant packs with different particle sizes; once the closure pressure exceeds 40 MPa, the proppant pack enters the fines-breakage stage, and the conductivity differences among various particle size blends become marginal. Furthermore, a semi-empirical prediction model incorporating a composite crushing factor (CCF) was developed based on the Kozeny–Carman relationship, enabling a rapid evaluation of fracture conductivity in deep coal–rock fractures. Overall, these results provide a practical basis for fracture conductivity prediction and hydraulic fracturing parameter optimization in coal–rock reservoirs. Full article

The use of a multi-component binder (MCB), consisting of Ordinary Portland Cement (OPC) combined with one or more supplementary cementitious materials (SCMs), has gained prominence for enhancing sustainability and improving the performance of cementitious systems. This study provides an integrated approach to optimize both binder composition and aggregate gradation through advanced mixture design and particle packing techniques. The MCB system consists of OPC partially replaced with SCMs such as fly ash (FA), Ground Granulated Blast Furnace Slag (GGBFS), metakaolin (MK), and silica fume (SF), with particle sizes ranging from micron to sub-micron scale. The D-optimal mixture design (DOD) method is used to determine the optimal material proportions by evaluating the relation between binder composition and wet packing density measured through the wet packing method (WPM). To further enhance packing efficiency, the Modified Toufar Model (MTM) is employed to optimize fine aggregate gradation. The maximum packing density is considered the primary criterion for identifying the optimal mix design, as it reflects the minimum void ratio and the most efficient particle size distribution. The optimized mortar mixes are evaluated for mechanical strength, pozzolanic reactivity, capillary water sorptivity, and drying shrinkage. Results indicate that the optimized MCB and optimized fine aggregate gradation improve the packing density and pozzolanic activity, significantly enhancing strength and durability performance. The incorporation of SCMs offers an effective strategy to improve performance while mitigating carbon emissions. Compared with C100, CFGMS-based systems achieved energy reductions of 35–40% and CO₂ emission reductions of 34–48%. Full article

Granular materials subjected to complex stress histories exhibit pronounced path dependence, multi-scale heterogeneity and scale-invariant characteristics, especially when particle breakage leads to gradation evolution with fractal features. Discrete element simulations are performed on granular assemblies with prescribed idealized fractal gradations under constant stress ratio loading–turning paths, while maintaining identical solid volume and initial relative density. The results show that, for a given gradation, both the peak strength envelope and the critical state line exhibit high consistency and are effectively independent of the examined stress paths, which are supported by high R² values from regression. At the critical state, microstructural parameters together with energy measures consistently follow stable power–law relationships with mean effective stress. For different gradations, the critical stress ratio remains nearly unchanged, whereas peak strength increases with increasing fractal dimensions; although critical state points remain nearly collinear in the deviatoric stress (q) –mean effective stress (p) plane, the critical state line in void ratio (e)–p plane shifts downward as the particle size distribution becomes broader. The evolution of microstructural and energy-related power–law relationships with fractal dimension exhibits a clear saturation trend. This study demonstrates that, within the simulated framework, fractal gradation primarily governs the position of the critical state in e–p space without altering its fundamental path-independent nature, providing fundamental insights into the multi-scale mechanics of graded granular materials under complex loading. Full article

The current gradation design of asphalt mixtures relies solely on sieve passing rates of single-sized aggregates. The quantitative evaluation of aggregate gradation is a challenge, considering the combined action of the geometric characteristics, size and passing rates of the aggregates. Analyzing the multi-dimensional geometric synergistic characteristics of graded aggregate can help to quantify the gradation. The AIMS II system was used to systematically and quantitatively evaluate the shape, angularity and texture of parameter distribution of single-sized aggregates. The synergistic effect of composite geometric characteristics on the mesoscopic interface behaviors was analyzed, and then a calculation model of aggregate gradation characteristic was established based on the gray relational analysis method. The results show that the lithology and source of aggregates govern the geometric characteristics indices of single-sized aggregates, whereas particle size controls the extent to which these geometric characteristics contribute to skeleton stability and interface interactions. A higher proportion of large-sized coarse aggregates results in a greater composite angularity index and a more stable skeleton structure within the asphalt mixture. Texture characteristics and particle size distribution are integrated into a unified composite texture index. As this index increases, the lubrication effect of asphalt on the aggregate skeleton becomes more pronounced. The aggregate gradation characteristic index demonstrates strong discriminative capability for different gradations and exhibits a robust linear correlation with aggregate–asphalt interfacial interaction indices. This index demonstrates strong capability to quantitatively describe the synergistic mechanism of multi-dimensional geometric characteristics and gradation types of asphalt mixtures. Full article

Digital image-based determination of aggregate and rock gradation has been only limitedly addressed in the existing literature despite its considerable potential to transform conventional material characterization practices in civil engineering. Rapid and accurate estimation of aggregate and rock particle size distributions using advanced image-based analytical methods can significantly improve efficiency, consistency, and scalability in design, construction, and quality control processes, particularly in large-scale structural and geotechnical engineering projects where traditional sieve analysis is time-consuming, labor-intensive, and difficult to apply under field conditions. In this study, an image-based methodology is proposed to rapidly detect aggregate particles and determine their size-based proportions within a pile by employing image enhancement, segmentation, and boundary detection algorithms. The results obtained from digital image processing are comparatively evaluated against experimental sieve analysis data, demonstrating a strong correlation between the two approaches. Low RMSE values achieved for larger aggregate sizes, such as 25.4 mm and 19 mm, indicate high detection accuracy, while the relatively higher yet acceptable RMSE values obtained for smaller particles, including 12.7 mm and 9.5 mm, confirm that the method maintains practical sensitivity across different size ranges. By analyzing samples collected from various aggregate and rock piles, the study further demonstrates the originality, robustness, and effectiveness of the proposed approach in evaluating heterogeneous material groups. Overall, the findings highlight that digital image-based determination offers a fast, reproducible, and non-destructive alternative to traditional sieve analysis, making it particularly valuable for reinforced concrete aggregate assessment and port fill rock characterization in large-scale structural and geotechnical engineering applications. Full article