WANG Zheng-cheng, LIU Song-yu, WU Kai, ZHANG Xiang, LI Meng-yao
Alkali residue is waste generated during the production of soda ash via the ammonia alkali process. Its excessive accumulation results in the wastage of land resources and environmental pollution. Alkali residue is used to partially replace cement in the production of alkali residue-based lightweight soil (A-LS), thus enabling its large-scale utilization. Compression, California bearing ratio (CBR), water-absorption, thermal-conductivity, and electrical-conductivity tests, as well as scanning electron microscopy and mercury intrusion porosimetry are conducted to systematically investigate the physical/mechanical properties and pore structure of A-LS. A-LS is used as a roadbed-filling material at the X204 bridgehead of the Xuwei-Guanyun section of the Lianyungang-Suqian expressway to monitor its temperature in real time. The results indicate that the compressive strength, CBR, flow value, and thermal conductivity of the A-LS increase with the wet density, whereas its water absorption and resistivity decrease. An approximately linear relationship exists between the wet density and each indicator. The average pore diameter and porosity are 82-179.86 nm and 57.78%-82.65%, respectively. At wet densities not exceeding 700 kg·m-3, the pores in the A-LS are predominantly macropores; however, when the wet density surpassed this limit, voids and microcracks are predominant. As the wet density increases, the volume proportion of macropores and tortuosity increase, whereas the mercury intrusion volume, median pore diameter, average pore diameter, most probable pore diameter, volume proportion of voids and microcracks, porosity, and fractal dimension decrease. As the volume proportion of voids and microcracks, pore diameter, and porosity increase, the compressive strength, CBR, flow value, and thermal conductivity decrease, whereas the water absorption and resistivity increase. Because of the hydration reactions of ordinary Portland cement and ground granulated blast furnace slag, a significant amount of heat is released, thus causing the internal temperature of the A-LS to increase rapidly to its peak value, followed by a decrease and then finally a stable state. Furthermore, the internal temperature of the A-LS remains unaffected by the atmospheric temperature. This demonstrates its excellent thermal-insulation properties, thus rendering it a viable option for application in permafrost regions. The A-LS possesses advantages such as large-scale consumption of alkali residues and cement conservation, thus presenting promising prospects for its widespread application.
