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Keywords = micromechanical characterization

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32 pages, 23012 KiB  
Article
A DEM Study on the Macro- and Micro-Mechanical Characteristics of an Irregularly Shaped Soil–Rock Mixture Based on the Analysis of the Contact Force Skeleton
by Chenglong Jiang, Lingling Zeng, Yajing Liu, Yu Mu and Wangyi Dong
Appl. Sci. 2025, 15(14), 7978; https://doi.org/10.3390/app15147978 - 17 Jul 2025
Viewed by 140
Abstract
The mechanical characteristics of soil–rock mixtures (S-RMs) are essential for ensuring geotechnical engineering stability and are significantly influenced by the microstructure’s contact network configuration. Due to the irregularity of particle shapes and the variability in particle grading with S-RMs, their macro-mechanical characteristics and [...] Read more.
The mechanical characteristics of soil–rock mixtures (S-RMs) are essential for ensuring geotechnical engineering stability and are significantly influenced by the microstructure’s contact network configuration. Due to the irregularity of particle shapes and the variability in particle grading with S-RMs, their macro-mechanical characteristics and mesoscopic contact skeleton distribution exhibit increased complexity. To further elucidate the macro-mesoscopic mechanical behavior of S-RMs, this study employed the DEM to develop a model incorporating irregular specimens representing various states, based on CT scan outlines, and applied flexible boundary conditions. A main skeleton system of contact force chains is an effective methodology for characterizing the dominant structural features that govern the mechanical behavior of soil–rock mixture specimens. The results demonstrate that the strength of S-RMs was significantly influenced by gravel content and consolidation state; however, the relationship is not merely linear but rather intricately associated with the strength and distinctiveness of the contact force chain skeleton. In the critical state, the mechanical behavior of S-RMs was predominantly governed by the characteristics of the principal contact force skeleton: the contact force skeleton formed by gravel–gravel, despite having fewer contact forces, exhibits strong contact characteristics and an exceptionally high-density distribution of weak contacts, conferring the highest shear strength to the specimens. Conversely, the principal skeleton formed through gravel–sand exhibits contact characteristics that are less distinct compared to those associated with strong contacts. Simultaneously, the probability density distribution of weak contacts diminishes, resulting in reduced shear strength. The contact skeleton dominated by sand–sand contact forces displays similar micro-mechanical characteristics yet possesses the weakest macroscopic behavior strength. Consequently, the concept of the main skeleton of contact force chains utilized in this study presents a novel research approach for elucidating the macro- and micro-mechanical characteristics of multiphase media. Full article
(This article belongs to the Section Civil Engineering)
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18 pages, 5837 KiB  
Article
Influential Microstructural Descriptors for Predicting Mechanical Properties of Fiber-Reinforced Composites
by Jamal F. Husseini, Eric J. Carey, Farhad Pourkamali-Anaraki, Evan J. Pineda, Brett A. Bednarcyk and Scott E. Stapleton
J. Compos. Sci. 2025, 9(7), 363; https://doi.org/10.3390/jcs9070363 - 12 Jul 2025
Viewed by 346
Abstract
Fiber-reinforced composites contain microscale features such as variations in local fiber volume fraction, fiber clusters, and resin-rich regions, which may impact mechanical properties. Microscale models need to be large enough to capture these features while maintaining high fidelity to capture the localized fiber-to-fiber [...] Read more.
Fiber-reinforced composites contain microscale features such as variations in local fiber volume fraction, fiber clusters, and resin-rich regions, which may impact mechanical properties. Microscale models need to be large enough to capture these features while maintaining high fidelity to capture the localized fiber-to-fiber interactions. This makes it difficult to efficiently model regions with equivalent fiber morphologies to as-manufactured scans and to perform large statistical studies to examine how these features drive mechanical performance. This study uses a novel microstructure generator and an efficient micromechanical model along with a characterization method that measures the geometry of these features to simulate a wide range of microstructures for strength and stiffness. After understanding how the mechanical properties are affected by morphology through correlation matrices, equivalent microstructures were generated to regions of an as-manufactured composite. The generation of microstructures based on different morphological descriptors allows for an understanding of which features are valuable when modeling these materials. In comparing microstructures with different equivalent descriptors to the case with all six descriptors, it was found that only using local fiber volume fraction median resulted in over predictions of strength and stiffness. Once two descriptors or more were introduced, such as local fiber volume fraction median and inter-quartile range, there was no significant difference in strength and stiffness. This suggests that at least two descriptors should be considered when generating equivalent microstructures for mechanical properties. Full article
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17 pages, 3175 KiB  
Article
Study on Performance Optimization of Red Mud–Mineral Powder Composite Cementitious Material Based on Response Surface Methodology
by Chao Yang, Qiang Zeng, Jun Hu and Wenbo Zhu
Buildings 2025, 15(13), 2339; https://doi.org/10.3390/buildings15132339 - 3 Jul 2025
Viewed by 243
Abstract
Red mud, a highly alkaline industrial by-product generated during aluminum smelting, poses serious environmental risks such as soil alkalization and ecological degradation. In this study, response surface methodology (RSM) was integrated with advanced microstructural characterization techniques to optimize the performance of red mud–slag [...] Read more.
Red mud, a highly alkaline industrial by-product generated during aluminum smelting, poses serious environmental risks such as soil alkalization and ecological degradation. In this study, response surface methodology (RSM) was integrated with advanced microstructural characterization techniques to optimize the performance of red mud–slag composite cementitious materials through multi-factor analysis. By constructing a four-factor interaction model—including red mud content, steel fiber content, alkali activator dosage, and calcination temperature—a systematic mix design and performance prediction framework was established, overcoming the limitations of traditional single-factor experimental approaches. The optimal ratio was determined via multi-factor RSM analysis as follows: the 28-day flexural strength and compressive strength of the specimens reached 12.26 MPa and 69.83 MPa, respectively. Furthermore, XRD and SEM-EDS analyses revealed the synergistic formation of C-S-H and C-A-S-H gels, and their strengthening effects at the fiber–matrix interfacial transition zone (ITZ), elucidating the micro-mechanism pathway of “gel densification–rack filling–strength enhancement.” This work not only enriches the theoretical foundation for the design of red mud-based binders but also offers practical insights and empirical evidence for their engineering applications, highlighting substantial potential in the development of sustainable building materials and high-value utilization of industrial solid waste. Full article
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23 pages, 11820 KiB  
Article
High-Speed Nanoindentation and Local Residual Stress Analysis for Cut Edge Damage in Complex Phase Steels for Automotive Applications
by Laia Ortiz-Membrado, Sergi Parareda, Daniel Casellas, Emilio Jiménez-Piqué and Antonio Mateo
Metals 2025, 15(6), 651; https://doi.org/10.3390/met15060651 - 11 Jun 2025
Viewed by 1127
Abstract
Advanced high-strength steels (AHSSs) are used as lightweight solutions for vehicles, mainly focusing on the Body-in-White. However, the implementation of such steels for chassis parts requires a profound knowledge of the key design parameters for these components, particularly those concerning fatigue performance. Manufacturing [...] Read more.
Advanced high-strength steels (AHSSs) are used as lightweight solutions for vehicles, mainly focusing on the Body-in-White. However, the implementation of such steels for chassis parts requires a profound knowledge of the key design parameters for these components, particularly those concerning fatigue performance. Manufacturing of chassis parts include mechanical cutting operations. Therefore, the deformation and damage induced at the cut edge may affect the fatigue resistance of the parts in service. To characterize and study this critical area, damage and micromechanical properties have been evaluated at the cut edge for three different AHSS grades, CP800, CP980, and DP600, analyzing the impact of cutting parameters and post-processing treatments, such as sandblasting. Large high-speed nanoindentation maps of 400 × 200 µm2 have been carried out along the cut edge in the three different target zones: burnish, fracture, and burr. In the hardness maps, the deformation lines and the gradient of hardness with increasing distance from the cut edge are perfectly observed. Residual stresses at the target zones of the cut edges were measured using the FIB-DIC method for CP980 to complement the micromechanical study in these critical areas. The results found show that reduced cutting clearance leads to larger hardened zones and favorable compressive stress distributions, correlating with improved fatigue resistance. Hardened zones extending up to 100 µm from the cut edge and compressive residual stresses exceeding −300 MPa were observed at low clearance. These findings are consistent with numerical simulations and previous fatigue tests, highlighting the potential of combining high-speed nanoindentation and local stress analysis for optimizing shear cutting processes in AHSS components. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Behavior of High-Strength Steel)
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17 pages, 10560 KiB  
Article
Optimization Design and Mechanical Performance Study of Carbon Fiber-Reinforced Composite Load-Carrying Structures for Subway Driver Cabin
by Jinle Wang, Bing Yang, Honglei Tian, Wenbin Wang and Xu Sang
Materials 2025, 18(11), 2524; https://doi.org/10.3390/ma18112524 - 27 May 2025
Viewed by 484
Abstract
This study systematically investigates the optimization design and mechanical performance of carbon fiber-reinforced polymer (CFRP) load-carrying structures for subway driver cabins to meet the lightweight demands of rail transit. Through experimental testing and micromechanical modeling, the mechanical properties of CFRP and foam core [...] Read more.
This study systematically investigates the optimization design and mechanical performance of carbon fiber-reinforced polymer (CFRP) load-carrying structures for subway driver cabins to meet the lightweight demands of rail transit. Through experimental testing and micromechanical modeling, the mechanical properties of CFRP and foam core materials were characterized, with predicted elastic constants exhibiting an error of ≤5% compared with experimental data. A shape optimization framework integrating mesh morphing and genetic algorithms achieved a 22% mass reduction while preserving structural performance and maintaining load-carrying requirements. Additionally, a stepwise optimization strategy combining free-size, sizing, and stacking sequence optimization was developed to enhance layup efficiency. The final design reduced the total mass by 29.1% compared with the original model, with all failure factors remaining below critical thresholds across three loading cases. The increased failure factor confirmed that the optimized structure effectively exploited the material’s potential while eliminating redundancy. These findings provide valuable theoretical and technical insights into lightweight CFRP applications in rail transit, demonstrating significant improvements in structural efficiency, safety, and manufacturability. Full article
(This article belongs to the Special Issue Engineering Materials and Structural Integrity)
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18 pages, 6158 KiB  
Article
Study of Mechanisms and Protective Strategies for Polymer-Containing Wastewater Reinjection in Sandstone Reservoirs
by Jie Cao, Liqiang Dong, Yuezhi Wang and Liangliang Wang
Processes 2025, 13(5), 1511; https://doi.org/10.3390/pr13051511 - 14 May 2025
Viewed by 422
Abstract
Wastewater reinjection is an important measure for balancing the sustainable development of petroleum resources with environmental protection. However, the polymer-containing wastewater generated after polymer injection presents challenges such as reservoir damage and waterflooded zone identification in oilfields. To address this, this study systematically [...] Read more.
Wastewater reinjection is an important measure for balancing the sustainable development of petroleum resources with environmental protection. However, the polymer-containing wastewater generated after polymer injection presents challenges such as reservoir damage and waterflooded zone identification in oilfields. To address this, this study systematically examined the impact of injection water with varying salinities on the flow characteristics and electrical responses of low-permeability reservoirs, based on rock-electrical and multiphase displacement experiments. Additionally, this study analyzed the factors influencing the damage to reservoirs during polymer-containing wastewater reinjection. Mass spectrometry, chemical compatibility tests, and SEM-based micro-characterization techniques were employed to reveal the micro-mechanisms of reservoir damage during the reinjection process, and corresponding protective measures were proposed. The results indicated the following: (1) The salinity of injected water significantly influences the electrical response characteristics of the reservoir. When low-salinity wastewater is injected, the resistivity–saturation curve exhibits a concave shape, whereas high-salinity wastewater results in a linear and monotonically increasing trend. (2) Significant changes were observed in the pore-throat radius distribution before and after displacement experiments. The average frequency of throats within the 0.5–2.5 µm range increased by 1.894%, while that for the 2.5–5.5 µm range decreased by 2.073%. In contrast, changes in the pore radius distribution were relatively minor. Both the experimental and characterization results suggest that pore-throat damage is the primary form of reservoir impairment following wastewater reinjection. (3) To mitigate formation damage during wastewater reinjection, a combined physical–chemical deblocking strategy was proposed. First, multi-stage precision filtration would be employed to remove suspended solids and oil contaminants. Then, a mildly acidic organic-acid-based compound would be used to inhibit the precipitation of metal ions and dissolve the in situ blockage within the core. This integrated approach would effectively alleviate the reservoir damage associated with wastewater reinjection. Full article
(This article belongs to the Special Issue Recent Developments in Enhanced Oil Recovery (EOR) Processes)
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21 pages, 8880 KiB  
Article
Impact of Acid Hydrolysis on Morphology, Rheology, Mechanical Properties, and Processing of Thermoplastic Starch
by Saffana Kouka, Veronika Gajdosova, Beata Strachota, Ivana Sloufova, Radomir Kuzel, Zdenek Stary and Miroslav Slouf
Polymers 2025, 17(10), 1310; https://doi.org/10.3390/polym17101310 - 11 May 2025
Viewed by 564
Abstract
We modified native wheat starch using 15, 30, and 60 min of acid hydrolysis (AH). The non-modified and AH-modified starches were converted to highly homogeneous thermoplastic starches (TPSs) using our two-step preparation protocol consisting of solution casting and melt mixing. Our main objective [...] Read more.
We modified native wheat starch using 15, 30, and 60 min of acid hydrolysis (AH). The non-modified and AH-modified starches were converted to highly homogeneous thermoplastic starches (TPSs) using our two-step preparation protocol consisting of solution casting and melt mixing. Our main objective was to verify if AH can decrease the processing temperature of TPS. All samples were characterized in detail by microscopic, spectroscopic, diffraction, thermomechanical, rheological, and micromechanical methods, including in situ measurements of torque and temperature during the final melt mixing step. The experimental results showed that (i) AH decreased the average molecular weight preferentially in the amorphous regions, (ii) the lower-viscosity matrix in the AH-treated starches resulted in slightly higher crystallinity, and (iii) all AH-modified TPSs with a less viscous amorphous phase and higher content of crystalline phase exhibited similar properties. The effect of the higher crystallinity predominated at a laboratory temperature and low deformations, resulting in slightly stiffer material. The effect of the lower viscosity dominated during the melt mixing, where the shorter molecules acted as a lubricant and decreased the in situ measured processing temperature. The AH-induced decrease in the processing temperature could be beneficial for energy savings and/or possible temperature-sensitive admixtures for TPS systems. Full article
(This article belongs to the Special Issue Optimization, Properties and Application of Polysaccharides)
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22 pages, 9537 KiB  
Article
Study on Wellbore Stability of Shale–Sandstone Interbedded Shale Oil Reservoirs in the Chang 7 Member of the Ordos Basin
by Yu Suo, Xuanwen Kong, Heng Lyu, Cuilong Kong, Guiquan Wang, Xiaoguang Wang and Lingzhi Zhou
Processes 2025, 13(5), 1361; https://doi.org/10.3390/pr13051361 - 29 Apr 2025
Cited by 1 | Viewed by 420
Abstract
Wellbore instability is a major constraint in large-scale shale oil extraction. This study focuses on the shale–sandstone interbedded shale oil reservoirs in the Chang 7 area, delving into the evolutionary principles governing wellbore stability in horizontal drilling operations within these formations. A geological [...] Read more.
Wellbore instability is a major constraint in large-scale shale oil extraction. This study focuses on the shale–sandstone interbedded shale oil reservoirs in the Chang 7 area, delving into the evolutionary principles governing wellbore stability in horizontal drilling operations within these formations. A geological feature analysis of shale–sandstone reservoir characteristics coupled with rigorous mechanical experimentation was undertaken to investigate the micro-mechanisms underpinning wellbore instability. The Mohr–Coulomb failure criterion applicable to sandstone and the multi-weakness planes failure criterion of shale were integrated to analyze the stress distribution of surrounding rocks within horizontal wells, facilitating the computation of collapse pressure and fracture pressure. A finite element model of wellbore stability in shale–sandstone horizontal drilling was established, and then we conducted a comprehensive analysis of the impacts of varying elastic moduli, Poisson’s ratio, and in-situ stress on wellbore stability. The findings reveal that under varying confining pressures, the predominant failure mode observed in most sandstone samples is characterized by inclined shear failure, coupled with a reduced incidence of crack formation. The strength of shale escalates proportionally with increasing confining pressure, resulting in a reduced susceptibility to failure along its inherent weak planes. This transition is characterized by a gradual shift from the prevalent mode of longitudinal splitting towards inclined shear failure. As the elastic modulus of shale rises, the discrepancy between circumferential and radial stresses decreases. In contrast, with the increasing elastic modulus of sandstone, the gap between circumferential and radial stresses widens, potentially inducing potential instabilities in the wellbore. An increase in sandstone’s Poisson’s ratio corresponds to a proportional increase in the difference between circumferential and radial stresses. Under reverse fault stress regimes, wellbore collapse and instability are predisposed to occur. Calculations of collapse pressure and fracture pressure reveal that the safety density window is minimized at the interface between shale and sandstone, rendering it susceptible to wellbore instability. These research findings offer significant insights for the investigation of wellbore stability in interbedded shale–sandstone reservoirs contributing to the academic discourse in this field. Full article
(This article belongs to the Special Issue Advanced Research on Marine and Deep Oil & Gas Development)
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20 pages, 2892 KiB  
Article
Untapped Potential of Recycled Thermoplastic Blends in UD Composites via Finite Element Analysis
by Pei Hao, Ninghan Tang, Juan Miguel Tiscar and Francisco A. Gilabert
Polymers 2025, 17(9), 1168; https://doi.org/10.3390/polym17091168 - 25 Apr 2025
Viewed by 427
Abstract
The increasing demand for fully recyclable composites has spurred extensive research on thermoplastics, valued for their recyclability and excellent mechanical properties. High-performance thermoplastics such as PEEK and PPS have been widely adopted in aerospace applications due to their outstanding load-bearing capabilities, which are [...] Read more.
The increasing demand for fully recyclable composites has spurred extensive research on thermoplastics, valued for their recyclability and excellent mechanical properties. High-performance thermoplastics such as PEEK and PPS have been widely adopted in aerospace applications due to their outstanding load-bearing capabilities, which are well documented. Recently, thermoplastic polymer blends have gained attention for their enhanced recyclability and sustainability, as well as their ability to improve thermal stability, viscosity, and manufacturability. However, limited data are available on the mechanical characterization of composites that incorporate these blends, particularly when recycled thermoplastics are used. In this study, we first examine the stress–strain behavior of the following three polymer blends relevant for structural applications: PES/PEEK, PPS/PEEK, and HDPE/PP. We then perform a numerical analysis to predict the mechanical performance of unidirectional fiber-reinforced composites using each blend as the matrix. This involves a micromechanical Representative Volume Element (RVE) approach combined with an advanced polymer model previously validated against experimental data. The findings are discussed to critically assess the suitability of these blends for producing fully matrix-recycled composites. Full article
(This article belongs to the Special Issue Modeling of Polymer Composites and Nanocomposites)
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22 pages, 7280 KiB  
Article
Research on the Thermal Conductivity and Microstructure of Calcium Lignosulfonate-Magnesium Oxide Solidified Loess
by Yuwen Lu and Wuyu Zhang
Appl. Sci. 2025, 15(8), 4545; https://doi.org/10.3390/app15084545 - 20 Apr 2025
Cited by 1 | Viewed by 386
Abstract
Loess, characterized by high porosity, a loose structure, and weak cementation, is highly prone to deformation and cracking under thermal stress, which significantly affects the bearing capacity of foundations and the stability of underground engineering structures. This study introduces an innovative approach that [...] Read more.
Loess, characterized by high porosity, a loose structure, and weak cementation, is highly prone to deformation and cracking under thermal stress, which significantly affects the bearing capacity of foundations and the stability of underground engineering structures. This study introduces an innovative approach that utilizes the eco-friendly modifier calcium lignosulfonate (CL) in combination with magnesium oxide (MgO) for the carbonation solidification treatment of loess. The research systematically investigated the thermal conductivity and underlying micro-mechanisms of the treated soil. A series of tests, including analyses of basic physical properties, measurements of thermal conductivity, X-ray diffraction (XRD), and scanning electron microscopy (SEM), were conducted to evaluate the effects of CL dosage, freeze–thaw cycles, moisture content, and dry density on the thermal conductivity of carbonation-solidified loess. The results indicate that carbonated solidified loess absorbed approximately 6% of CO2, while effectively reducing its collapsibility grade to a slightly collapsible classification. Additionally, its thermal conductivity decreased by 16.7%, thereby mitigating the influence of various environmental factors. Based on the experimental results, a microscopic mechanism model was developed. This study presents a sustainable and innovative technical solution for stabilizing loess foundations in cold regions. Full article
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19 pages, 7626 KiB  
Article
Nanoindentation-Based Characterization of Mesoscale Mechanical Behavior in Dolomite Crystals
by Majia Zheng, Zhiwen Gu, Hao Dong, Tinghu Ma and Ya Wu
Processes 2025, 13(4), 1203; https://doi.org/10.3390/pr13041203 - 16 Apr 2025
Viewed by 528
Abstract
Conventional rock mechanical testing approaches encounter significant limitations when applied to deeply buried fractured formations, constrained by formidable sampling difficulties, prohibitive costs, and intricate specimen preparation demands. This investigation pioneers an innovative nanoindentation-based multiscale methodology (XRD–ED–SEM integration) that revolutionizes the mechanical characterization of [...] Read more.
Conventional rock mechanical testing approaches encounter significant limitations when applied to deeply buried fractured formations, constrained by formidable sampling difficulties, prohibitive costs, and intricate specimen preparation demands. This investigation pioneers an innovative nanoindentation-based multiscale methodology (XRD–ED–SEM integration) that revolutionizes the mechanical characterization of dolostone through drill cuttings analysis, effectively bypassing conventional coring requirements. Our integrated approach combines precision surface polishing with advanced indenter calibration protocols, enabling the continuous stiffness method to achieve unprecedented measurement accuracy in determining micromechanical properties—notably an elastic modulus of 119.47 GPa and hardness of 5.88 GPa—while simultaneously resolving complex indentation size effect mechanisms. The methodology reveals three critical advancements: remarkable 92.7% dolomite homogeneity establishes statistically significant elastic modulus–hardness correlations (R2 > 0.89), while residual imprint analysis uncovers a unique brittle–plastic interaction mechanism through predominant rhomboid plasticity (84% occurrence) accompanied by microscale radial cracking (2.1–4.8 μm). Particularly noteworthy is the identification of load-dependent property variations, where surface hardening effects and defect interactions cause 28.7% parameter dispersion below 50 mN loads, progressively stabilizing to <8% variance at higher loading regimes. By developing a micro–macro bridging model that correlates nanoindentation results with triaxial test data within a 12% deviation, this work establishes a groundbreaking protocol for carbonate reservoir evaluation using minimal drill cutting material. The demonstrated methodology not only provides crucial insights for optimizing hydraulic fracture designs and wellbore stability assessments, but it also fundamentally transforms microstructural analysis paradigms in geomechanics through its successful application of nanoindentation technology to complex geological systems. Full article
(This article belongs to the Topic Green Mining, 2nd Volume)
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23 pages, 12386 KiB  
Article
Interfacial Damage Mechanisms and Performance Prediction in Recycled Aggregate Concrete
by Siyu Zhang, Yongcheng Ji and Xiangwei Hao
Coatings 2025, 15(4), 441; https://doi.org/10.3390/coatings15040441 - 8 Apr 2025
Viewed by 515
Abstract
To address the growing demand for sustainable construction and efficient recycling of waste concrete resources, this study investigates the interfacial performance and mechanical property prediction of recycled aggregate concrete (RAC) under varying recycled aggregate (RA) replacement ratios (r = 0%, 30%, 60%, 100%). [...] Read more.
To address the growing demand for sustainable construction and efficient recycling of waste concrete resources, this study investigates the interfacial performance and mechanical property prediction of recycled aggregate concrete (RAC) under varying recycled aggregate (RA) replacement ratios (r = 0%, 30%, 60%, 100%). A comprehensive experimental program was implemented, including uniaxial compression tests and microscopic characterization using scanning electron microscopy (SEM), to evaluate the macro- and microscale damage evolution and interfacial transition zone (ITZ) properties of RAC. Based on Weibull’s statistical strength theory, a constitutive model for RAC under compression was developed, and a two-dimensional random aggregate model was implemented in Abaqus to simulate the damage initiation and propagation processes at different replacement ratios. The results demonstrate that the compressive strength of RAC decreases as the RA replacement ratio increases, while the optimal interfacial and mechanical performance is achieved at a 30% replacement ratio. The study reveals that failure in RAC initiates at the ITZ between the recycled aggregates and cement matrix, subsequently propagating to complete structural failure. The proposed constitutive model accurately predicts the stress–strain behavior of RAC across different replacement ratios, showing excellent agreement with experimental data. These findings provide valuable insights into the interfacial performance and failure mechanisms of RAC, offering a theoretical foundation for optimizing the design and application of recycled aggregate concrete in sustainable engineering projects. Full article
(This article belongs to the Special Issue Surface Treatments and Coatings for Asphalt and Concrete)
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30 pages, 29741 KiB  
Article
Evolution Characteristics of Pore–Fractures and Mechanical Response of Dehydrated Lignite Based on In Situ Computed Tomography (CT) Scanning
by Shuai Yan, Lijun Han, Shasha Zhang, Weisheng Zhao and Lingdong Meng
Fractal Fract. 2025, 9(4), 220; https://doi.org/10.3390/fractalfract9040220 - 31 Mar 2025
Viewed by 425
Abstract
Based on the uniaxial compression tests and in situ CT scanning experiments of lignite with different dehydration times and the fractal theory, this paper qualitatively and quantitatively investigated the influence of the dehydration effect on the evolution of pore–fractures and the mechanical behavior [...] Read more.
Based on the uniaxial compression tests and in situ CT scanning experiments of lignite with different dehydration times and the fractal theory, this paper qualitatively and quantitatively investigated the influence of the dehydration effect on the evolution of pore–fractures and the mechanical behavior of lignite under uniaxial compression conditions. The results show that the dehydration effect significantly affects the pre-peak deformation and post-peak failure behavior of lignite but has no significant impact on its peak strength. The pore–fracture parameters, such as the fractal dimension, surface porosity, and fracture volume, of three samples all exhibit an evolutionary pattern of “continuous decrease in the compaction and elastic stages–gradual increase in the plastic stage–sharp growth in the post-peak stage” with the dynamic evolution of the pore–fractures. However, the dehydration effect leads to an increase in the intensity of pore–crack evolution and a nonlinear rise in all the parameters characterizing the pore–crack complexity during uniaxial compression, which, in turn, leads to an increment in the fluctuation of the above evolutionary trends. The mechanism underlying the differential influence of the dehydration effect on the macroscopic mechanical behavior of lignite is follows: The dehydration effect non-linearly and positively affects the initial pore–fracture structure of lignite, thereby non-linearly and positively promoting the evolution of pore–fractures during the loading process. Nevertheless, since it fails to weaken the micro-mechanical properties of lignite and cannot form effective through-going fractures, it has no significant impact on the uniaxial compressive strength of the coal samples. The findings of this study can provide some references for the support design and deformation control of underground lignite roadways. Full article
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22 pages, 4517 KiB  
Article
Characterizing the Interaction Between Asphalt and Mineral Fillers in Hot Mix Asphalt Mixtures: A Micromechanical Approach
by Shuang Wang, Zhichen Wang, Ankang Yu, Huanan Yu, Zhongming He, Xiangzhu Meng, Zhi Gong, Deqing Guan and Fuli Zhang
Appl. Sci. 2025, 15(5), 2735; https://doi.org/10.3390/app15052735 - 4 Mar 2025
Viewed by 695
Abstract
Asphalt mastic serves as a critical binding material in hot mix asphalt mixtures, significantly influencing the performance and durability of asphalt pavements. The interaction between asphalt and mineral fillers directly affects the binding properties of the mastic. In this study, the adsorbed asphalt [...] Read more.
Asphalt mastic serves as a critical binding material in hot mix asphalt mixtures, significantly influencing the performance and durability of asphalt pavements. The interaction between asphalt and mineral fillers directly affects the binding properties of the mastic. In this study, the adsorbed asphalt film thickness was used as an indicator to evaluate the interaction between asphalt and mineral fillers. A micromechanical approach was proposed to calculate this thickness, and the results were compared using the Hashin model, the Mori–Tanaka model, and the generalized self-consistent model. The results demonstrate that the adsorbed asphalt film thickness, as determined using the micromechanical approach, ranged from 0.01 to 0.37 µm. The Hashin model was found to provide the most accurate characterization of the interaction between the asphalt and the mineral fillers. The order of adsorbed asphalt film thickness was as follows: coal gangue asphalt mastic > limestone asphalt mastic > fly ash asphalt mastic. Higher concentrations of acidic SiO2 in the mineral fillers resulted in a weaker interaction between the asphalt and the fillers. When the temperature was below the softening point of the asphalt, the interaction strength decreased as frequency increased. Conversely, when the temperature exceeded the softening point, the interaction strength increased with frequency. The effect of temperature on the interaction capability was further influenced by the characteristics of the mineral fillers. The micromechanical-based method proposed in this study eliminates the dependency of the evaluation indicator on the volume fraction of mineral fillers, thereby providing a more accurate characterization of the interaction between asphalt and fillers. This approach provides a theoretical foundation to guide the design of asphalt mixtures. Full article
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18 pages, 6461 KiB  
Article
Microscopic Mechanical Properties and Physicochemical Changes of Cement Paste Exposed to Elevated Temperatures and Subsequent Rehydration
by Lei Xu, Xiaochuan Hu, Ruifeng Tang, Xin Zhang, Yan Xia, Bo Ran, Jinlong Liu, Shiyu Zhuang and Weichen Tian
Materials 2025, 18(5), 1050; https://doi.org/10.3390/ma18051050 - 27 Feb 2025
Cited by 1 | Viewed by 662
Abstract
The effect of elevated temperatures and subsequent rehydration on the microscopic mechanical properties and physicochemical changes of cement pastes was investigated. Cement pastes with different grades (CEM I 42.5, CEM I 52.5) and different water-to-cement ratios (0.3, 0.4) were exposed to target temperatures [...] Read more.
The effect of elevated temperatures and subsequent rehydration on the microscopic mechanical properties and physicochemical changes of cement pastes was investigated. Cement pastes with different grades (CEM I 42.5, CEM I 52.5) and different water-to-cement ratios (0.3, 0.4) were exposed to target temperatures of 300 °C, 600 °C, and 900 °C, followed by rehydration. Several characterization techniques, including the Vickers microhardness test, X-ray diffraction, thermogravimetry, and 1H Nuclear Magnetic Resonance spectroscopy, were employed to assess changes in the microscopic mechanical and physicochemical properties of the cement pastes resulting from the heating and rehydration treatments. The results indicate that the cement pastes with higher grades and a higher water-to-cement ratio exhibit better resistance to high temperatures. The heating process alters the water distribution and structure of C-S-H gel, leading to the collapse of its interlayer structure and an increase in gel porosity. Elevated temperatures (300 °C and 600 °C), followed by rehydration, enhance the Vickers microhardness of the cement pastes. However, excessively high temperatures (900 °C) weaken the micro-mechanical properties and may cause damage. Cement pastes heated to 600 °C show a more significant recovery in micro-mechanical properties compared to those heated at 300 °C, which is attributed to the rehydration of a new amorphous nesosilicate phase formed at 600 °C. Full article
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