This study aims to investigate the effect of calcium sulfate whisker (CSW) on the properties and microstructure of cement-based composites. Further, nanosilica (NS) was used as a comparison. The results show that the compressive strength and fracture toughness of cement-based composites increased by 10.3% and 10.2%, respectively, with 2% CSW. The flexural strength, splitting tensile strength, and fracture energy increased by 79.7, 34.8 and 28.7%, respectively, with 1% CSW. With the addition of CSW, shrinkage deformation was aggravated, and the capillary water absorption coefficients were clearly reduced. Compared with NS, CSW-reinforced cement-based composites show better tensile, flexural, and fracture properties and smaller shrinkage deformations and capillary water absorption coefficients. The residual mechanical properties of all groups improve when the treating temperature is lower than 400 °C and decline rapidly when the temperature goes over 600 °C. When treated at 900 °C, the residual mechanical properties are 40% less than those at ambient temperature, with the NS group showing the best performance, followed by the control group and the CSW group. X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests show that the addition of CSW improves the microstructure of the matrix. CSW can reinforce and toughen composites by generating ettringite and whisker pullout, whisker breakage, crack bridging, and crack deflection at the microstructure level.

This work aimed to investigate the fracture resistance of asphalt mixtures containing graphene oxide (GO) using fracture mechanics. Three dense-graded asphalt mixtures with 9.5, 13.2, and 16 mm nominal maximum aggregate size (NMAS) were modified with varying GO contents. Semi-circular bending (SCB) fracture tests were conducted to determine the fracture properties of the asphalt mixtures. Results showed that mode I fracture toughness (K_IC) and fracture energy (G_f) at −20 °C, −10 °C, and 0 °C were significantly improved with the addition of GO. Likewise, increasing trends in J-integral were observed with increasing GO content at 0 °C, 10 °C, and 20 °C. The variations of the fracture mechanic parameters suggested that adding GO could help in enhancing the fracture performance at low and intermediate temperatures. The fracture properties showed a high dependency on test temperature. An increase in NMAS resulted in increased fracture strength of the mixtures. Additionally, a two-parameter Weibull distribution model was utilised to further investigate the fracture results. The fracture toughness of the asphalt mixtures was found to comply with the two-parameter Weibull distribution. Response surface methodology (RSM) was used to develop prediction models for the fracture properties. The proposed models exhibited a high degree of correlation.

Thermal damage assessment of cementitious composites is essential for evaluating post-fire health conditions of the engineering structures, as well as the basis for reinforcement and repair after fires. Fibers and fly ash are widely used in cementitious composites due to their excellent properties. However, quantifying and predicting the thermal damage of hybrid fibers reinforced cementitious composites blended with fly ash at high temperatures is still inexplicit. Hence, this study aims to realize multiscale prediction of thermal damage for hybrid fibers reinforced cementitious composites blended with fly ash at high temperatures. First, the volumes of the phase compositions during hydration and dehydration are calculated by the hydration of cement and fly ash and the dehydration of hydration products. Then, a multiscale model is established to predict the thermal damage of hybrid fibers reinforced cementitious composites and verified by the experimental data. At last, the temperature field of tunnel lining structure in fires is obtained by numerical modeling and employing it to predict thermal damage at different thicknesses and moments. Results show that the heating rate determines the dehydration degree of hydration products and the volumes of the phase composites at high temperatures. The proposed multiscale model can reflect the thermal microcracking of cement paste, the interfacial thermal damage between aggregates and the cement paste, and the deterioration of elastic modulus of fibers. After three hours of exposure to fires, serious damage appears at the surface and the thickness of 2 cm and 5 cm of the lining, while there is nearly no damage at a thickness of 30 cm or more.

Freeze–thaw cycles and the soil compaction coefficient ($\lambda \mathrm{c}$) have significant influence on the plastic strain for the foundation of underground structures in seasonal permafrost regions. Understanding the microstructural evolution of freeze–thawed soil is pivotal for assessing the long-term settlement of infrastructure foundation under repeated train loading. This study investigates the impacts of freeze–thaw cycles and $\lambda \mathrm{c}$ on the plastic strain and pore size distribution (PSD), as well as fractal characteristics, of soft clay via a set of cyclic triaxial tests and nuclear magnetic resonance (NMR) analyses. Fractal theory was adopted to analyze the heterogeneity of soil specimens. The results showed that an increase in $\lambda \mathrm{c}$ could efficiently alleviate the cumulative plastic strain. It also decreased the proportion of large pores and facilitated the generation of small and medium-sized pores. The analysis of the NMR test demonstrated that the freeze–thaw cycle led to the disruption of the soil’s microporous structure. Moreover, a higher value of $\lambda \mathrm{c}$ encouraged the formation of a more intricate and uniform pore structure. This, in turn, increased the fractal dimension, enhanced the structural heterogeneity, and thereby improved the soil’s structural complexity and its resistance to deformation. These findings underscore the significance of achieving optimal compaction levels to bolster soil stability under freeze–thaw conditions, provide valuable guidance for infrastructure design in permafrost regions, and help to ensure the durability and stability of transportation networks, such as railways and roads, over time.

In recent years, increasing attention has been paid to the impact of vibrations generated by operating subway trains on the surrounding environment. However, the dynamic response occurring below the moving load of the train remains poorly understood, presenting a highly complicated issue. To address this challenge, a 2.5-dimensional finite element method was applied, aimed at calculating and predicting the vibration and deformation of subway tunnels and foundations swiftly and accurately. Specifically, this study focused on analyzing the vibration characteristics of the rectangular tunnel in Ningbo Rail Transit Line 3 (Zhejiang Province, China). The analysis evaluated the influence of key factors—including tunnel burial depth, foundation soil properties, and train speed—on vibrations in the tunnel’s foundations and tracks under operational loads. Results indicated that higher train speeds, shallower tunnel depths, and lower soil shear wave velocities correlated with increased ground vibration intensity. This study offers valuable tools and insights for predicting ground vibrations and potentially enabling early warnings in the future.