Recycling and conservation of calcium carbide slag in dispersive soil modification: An evaluation of early age performance

The disposal of calcium carbide slag (CCS) is still a serious problem for areas that rely on the polyvinyl chloride industry, especially in the northern part of China. To assess the early effectiveness of CCS in treating dispersive soil, mechanical, chemical, and microscopic tests were conducted. The pH and conductivity EC were also measured to evaluate the effect of active ions. Validation test was also conducted on a natural dispersive soil from northern Shaanxi to prove the improving effectiveness of CCS on the dispersivity of soil. Results showed that adding 2% CCS significantly limits the dispersivity of the soil and improves its resistance to water erosion and mechanical properties. Increases of 11 times and 4.8 times were observed when CCS content increased from 0% to 5% and curing time increased from 0 to 28 days for compressive and tensile strength, respectively. The correlation between dispersivity and mechanical properties with pH and EC during curing was found to be significant. This relationship is closely linked to the dissolution and consumption behavior of the active ions that are abundant and contributed by the functional oxides in the CCS. Microscopic tests indicated that the porous particle structure of CCS improves the mechanical properties and limits the dispersivity of soil, due to physical strengthening and carbonization reaction in the early stage of CCS application. The subsequent release of Ca2+ and the formation of C-S-H/C-A-H cementitious hydrates played a vital role in controlling chemical dispersivity and further improving the mechanical properties of the dispersive soil. This was accomplished through ion replacement and pozzolanic reactions that were supported by the abundant active ions. Validation test show that CCS could efficiently improve the engineering properties of dispersive soil and the recommended mixture ratio is 2–5%.