Freeze-thaw cycling has a significant impact on the energy utilization and stability of roadbed fill. Given the good performance of basalt fiber (BF) and plant fiber (PF), a series of indoor tests are conducted on fiber-reinforced red clay (RC) specimens to analyze the shear strength, thermophysical, and microstructural changes and damage mechanisms of the RC under the freeze-thaw cycle-BF coupling, meanwhile, comparing the improvement effect of PF. The results indicate that the RC cohesion (c) first increases and then decreases with the increasing fiber content under BF improvement, reaching the maximum value at the content of 2%, and the change in the internal friction angle (phi) is relatively small. As the number of freeze-thaw cycles increases, cohesion (c) first decreases and then gradually stabilizes. The thermal conductivity increases with increasing moisture content, and the thermal effusivity increases and then decreases with increasing moisture content and fiber content. The heat storage capacity reaches the optimum level at a moisture content of 22.5% and a fiber content of 1%. Microanalysis reveals that at 2% fiber content, a fiber network structure is initially formed, and the gripping effect is optimal. The shear strength of PF-improved soil is higher than that of BF at a fiber content of 4-6%, and the thermal conductivity is better than that of BF. At the same fiber content, the heat storage and insulation capacity of BF-improved soil is significantly higher than that of PF.

In the context of sustainable building development, Compressed Earth Blocks (CEBs) have garnered increasing attention in recent years owing to their minimal environmental and economic impact. However, owing to the inherent diversity of raw soil and the production process's reliance on expertise, the properties of these blocks are subjected to multifaceted influences. Among these, the significance of soil particle size variation often remains overlooked, leaving its impact ambiguous. This study endeavours to address this gap in existing research by delving into this aspect. Two distinct batches of CEBs were produced by adjusting the grain size curve of a single type of sieved soil with different maximum mesh openings: 2 mm for R1 CEBs and 12.5 mm for R2 CEBs. Experimental results reveal significant differences in thermophysical characteristics: on average, R1 blocks show superior thermal performance, boasting a 23% reduction in thermal conductivity compared to R2 blocks, and are lighter, with an 8% decrease in dry bulk density. Although no significant changes in mechanical parameters were observed, finer-structured R1 blocks showed a 25% greater tendency to absorb water due to changes in their porous structure. This study sheds light on the sensitivity of thermal parameters to changes in soil particle size and shows that blocks with finer particles exhibit poorer heat conduction and heat diffusion. Besides providing new insights into the literature, this research also provides a strategic approach to optimise the thermophysical properties of CEBs. By understanding the influence of particle size, researchers and practitioners can now develop strategies to enhance these properties and improve the overall performance of CEBs.