Using soil tuff-modified polymetallic lead–zinc tailings sand to facilitate sustainable development of subgrade engineering

Abstract

The use of soil tuff, an industrial solid waste, for the modification of lead–zinc tailings as subgrade fillers presents a sustainable solution for concurrently addressing the negative impacts of tailings accumulation and resource depletion resulting from road construction. To demonstrate this, we conducted a thorough series of macroscopic and microscopic experiments, including the physical performance, durability, and microstructural behaviors of soil tuff-modified lead–zinc tailings sand (STM-LZTS) and cement-modified LZTS with varying modifier dosages, compaction degrees, and curing ages. Furthermore, we conducted a comprehensive comparison of the sustainability performance of these two modified LZTSs in terms of cost, CO2 emissions, and energy consumption. The results indicate that the incorporated 6% soil tuff filled the voids with the hydrated calcium silicate gel generated during the hydration process, which improved the structural stability. The CBR value was further enhanced to over 4% upon modification. With an increase in compaction degree to 96%, the CBR value escalated to over 8% (＞4%). The STM-LZTS specimens exhibited compressive strengths ranging from 0.818 to 0.958 (＞0.3 MPa). The variations in shear strength ranged between 200 and 550 kPa. Meanwhile, the modification of LZTS with soil tuff considerably delayed the deterioration of specimens under dry–wet, freeze–thaw, and salt-solution immersion conditions. Furthermore, compared with the cement-modified LZTS, the modified material formed a denser binder and a more robust nonparticle gel due to its lower calcium–silica ratio and higher aluminum–silica ratio, exhibiting superior performances in terms of compressive strength and resistance to salt corrosion. In addition, the use of soil tuff substantially reduced the cost, carbon emissions, and energy consumption, making it a promising and ecofriendly alternative for waste management and achieving carbon neutrality goals in subgrade engineering.