Study of micro-expansion deformation of cement-based materials enhanced by soybean-wax-coated carbide slag composites

The industrial solid waste carbide slag (CS) is composed mainly of calcium hydroxide (Ca(OH)₂), which produces calcium oxide (CaO) after calcination and can be used as a CaO-type expansion agent. However, the hydration reaction of calcined CS often occurs before the cement setting and hardening time, and the resulting expansion is ineffective, which limits the wide application of CS as a CaO expansion agent. In this study, a new type of swelling agent, soybean-wax-coated CS composite (CSCC), was prepared by using soybean wax (SW) to coat the calcined CS to delay its hydration. In this study, the microstructural composition of CSCC was investigated, and the hydration history and retardation characteristics and effects of CSCC with various mixing ratios were analysed. The micro-expansion deformation and strength development of CSCC cement-based materials were also investigated, and a micro-expansion model was established. The results showed that SW wrapped around the surface of CS particles formed a dense wrapping structure and effectively delayed hydration. Meanwhile, compared with CS, CSCC had an induction period in the hydration process due to the coating of SW, which greatly delayed the hydration of CS. Also, the optimum mixing ratio of CSCC was determined by analysing the delayed hydration onset time and the time of the second exothermic rate peak. It was also found that incorporating CSCC resulted in a significant increase in the micro-expansion deformation of the cementitious materials but a decrease in the compressive strength.