Abstract: Aiming at the problem of the high cement content of conventional foamed lightweight soil (FLS), a low-carbon FLS was developed by replacing cement with high proportions of clay and ground granulated blast furnace slag. Under the conditions of different wet densities (6~10 kN/m³) and water content (115%~140%), effects of dry-wet cycles on the mechanical properties of FLS were investigated, and the microstructural evolution of FLS before and after dry-wet cycles was analyzed using scanning electron microscopy (SEM). The results show that the unconfined compressive strength of FLS continues to increase with curing age, but the decrease of wet density or the increase of water content significantly weaken the growth trend of unconfined compressive strength. When the wet density is 8 kN/m³ and the water content is 115%, FLS can balance both flow value and strength requirements for embankment filling. After 10 dry-wet cycles, FLS shows no obvious cracking or disintegration in the appearance, and the loss of unconfined compressive strength is less than 15%, and the E50 decreases by 16.8% to 24.4%, demonstrating good durability under dry-wet cycles. The SEM results show that dry-wet cycles lead to microcracks and localized fragmentation on the pore walls of spherical gas bubbles, with crack widths ranging from 5 to 20 μm. The FLS with low wet density and high water content is more susceptible to damage by reducing pore wall thickness and weakened soil particle bonding. However, the temperature-enhanced pozzolanic reaction effectively alleviates microstructure degradation and maintains high structural durability.

Key words: foamed lightweight soil, clay, dry-wet cycle, mechanical property, microstructure