Waste red layers have the potential to be used as supplementary cementitious materials after calcination, but frequent and long-term dry-wet cycling leads to deterioration of their properties, limiting their large-scale application. In this study, the feasibility of using calcined red layers as cement replacement materials under dry-wet cycling conditions was analyzed. The damage evolution and performance degradation of calcined red layer-cement composites (RCC) were systematically evaluated via the digital image correlation (DIC) technique, scanning electron microscopy (SEM) analysis and damage evolution mode. The results show that the calcined red layer replacement ratio and number of dry-wet cycles affect the hydration and pozzolanic reactions of the materials and subsequently affect their mechanical properties. Based on the experimental data, a multiple regression model was developed to quantify the combined effects of the number of dry-wet cycles and the replacement ratio of the calcined red layer on the uniaxial compressive strength. As the number of dry-wet cycles increases, microcracks propagate, the porosity increases, and damage accumulation intensifies. In particular, at a high substitution ratio, the material properties deteriorate further. The global strain evolution process of a material can be accurately tracked via DIC technology. The damage degree index is defined based on strain distribution law, and a damage evolution model was constructed. At lower dry-wet cycles, the hydration reaction has a compensatory effect on damage. The pozzolanic reaction of the calcined red layer resulted in an increase in the number of dry-wet cycles. The RCC samples with high replacement ratios show significant damage accumulation with fast damage growth rates at lower stress levels. The model reveals the nonlinear effects of dry-wet cycling and the calcined red layer replacement ratio on damage accumulation in RCC. The study findings establish a scientific foundation for the resource utilization of abandoned red layers and serve as a significant reference for the durability design of materials in practical engineering applications.

Permafrost degradation induces the expansion of talik, which has high water content, low bearing capacity, and high compressibility, constantly threatening the safe and long-term service performance of local engineering structures and practices. Therefore, adopting effective measures to address talik is of vital significance for the effective operation of engineering projects in permafrost regions. Utilizing polyurethane-cement composite to solidify talik to improve its mechanical properties. Evaluate its applicability in cold regions by analyzing the thermal conditions and durability. Characterize the micro-mechanisms of the specimens by scanning electron microscopy, X-ray diffraction and mercury intrusion porosimetry. The results show that the talik solidified by WPU10 has good water stability and relatively low strength damage during the freeze-thaw cycles. Freeze-thaw cycles affect the pore structure, the morphology of hydration products within the specimens, and the effective porosities of PUC and WPU10 increase by 62.44% and 59.58%, respectively. The incorporation of WPU can inhibit the occurrence and development of hydration reactions, and delay the hydration process. WPU has an optimal dosage, with a 10% content having the best effect. An insufficient dosage fails to fill the pores effectively, whereas an excessive one causes agglomeration and influences the cement hydration process. The research results provide an important reference for the innovation and application development of engineering materials in cold regions, and also for the treatment of talik.

Understanding the mechanical behaviour of natural soils as mixed with cement for stabilization is crucial for civil engineering developments. The response of cement-soil admixtures when subjected to cyclic loads is a largely unexplored topic, despite the importance of understanding fatigue in these ubiquitous construction materials. We present cyclic loading experiments on Portland cement mixed with fragmented shale fragments using triaxial testing, monitored with synchrotron-based mu CT. Through digital volume correlation (DVC), the temporal evolution of the displacement, volumetric, and von Mises equivalent strain fields were obtained. We observed in detail the fatigue damage evolution during cyclic loading and found that following high-strain deformation of the much softer shale fragments, the ultimate failure of the samples occurred in the adjacent cement matrix. The failure mechanism under periodic stress and its relevance for accelerated laboratory testing of slow degradation long-term processes are of key importance to technical infrastructure, including subsea CO2 storage.

Foam lightweight soil (LS) is a cement composite with excellent lightness, but the excessive use of cement causes some negative impacts on the surrounding environment. This study aims to develop a sustainable cement composite by utilizing fly ash and waste soil in LS, providing a practical reference for green construction of road engineering. The physico-mechanical properties of cement composites with different mixing ratios were comparatively evaluated using geotechnical tests, and the micro-mechanisms were investigated using microscopic tests. The testing results showed that the utilization of fly ash and waste soil was unfavorable to improve the mechanical strength and the damage resistance of LS, but significantly decreased the use of cement. The comprehensive performance of cement composite reached the optimum when the replacement rates of fly ash and waste soil were 10% and 20%. Fly ash reacted with the hydration products of cement producing more cementitious gels to make the internal structure of cement composite denser, while waste soil not involved in its chemical reaction. The life cycle assessment indicated that the potential environmental impact of LS was improved after utilizing fly ash and waste soil, and the proposed sustainable cement composite had good feasibility in engineering.