Study on Strength Characteristics and Hardening Mechanism of Alkali Residue-Based Lightweight Soil

The accumulation of alkali residue has led to significant contamination of soil, air, and water, posing a hazardous threat to the environment. To address this issue, a technology and method for producing alkali residue-based lightweight soil were proposed to facilitate the reuse of alkali residue, and the feasibility of this method was demonstrated. Compression tests, X-ray diffraction, X-ray fluorescence spectrometry, and scanning electron microscope (SEM) were conducted to investigate the strength characteristics and hardening mechanism of the material. The results indicate that the compressive strength of the alkali residue-based lightweight soil increases linearly with wet density, age, content of portland cement, and ground granulated blast slag. The optimal water-solid ratio was determined to be 0.6. Specimens with low and high strength exhibited plastic and brittle failures, respectively. The primary contributors to the material's compressive strength were identified as hydrated calcium silicate, ettringite, monosulfur calcium sulfoaluminate hydrate, hydrated calcium aluminate, and Friedel's salt. The 28-d compressive strength of the alkali residue-based lightweight soil, with a water-solid ratio of 0.6 and a wet density of 800.0 kg/m3, was measured to be 1.17 MPa, meeting the requirements for most filling projects.