Experimental assessment of freeze–thaw characteristics and microscopic mechanisms of coal-based solid waste improved loess filler

Abstract

To tackle freeze–thaw damage in loess layers by seasonal freeze–thaw cycles (FTC) and the growing coal-based solid waste crisis in Northwest China, we propose using coal-based solid waste to enhance loess for more stable, sustainable infrastructure. This paper investigates the freeze–thaw behaviors and microscopic mechanisms of loess modified with 6%, 15% coal gasification slag (CGS) and 30%, 50% coal gangue (CGA), using FTC tests, SEM analysis, and CT scans. Key aspects were analyzed include frost heave, thaw settlement, temperature, moisture distribution, and microstructural changes. The results show that adding 15% CGS reduces average frost heave and thaw settlement by 72.6% and 70.8% during the first 2 FTC, while 50% CGA cuts frost heave by 62.5% over 5 FTC, demonstrating strong potential for freeze–thaw resistance. The addition of CGS and CGA can also reduce temperature fluctuation and thermal conductivity of loess, enhancing the internal temperature stability. Moreover, adding 50% CGA could help regulate water content distribution after FTC and densify the structure of improved loess, while adding CGS leads to aggregates formation within modified loess particles.