Strength development in silty clay stabilized with calcium carbide residue and fly ash

Calcium carbide residue (CCR) and fly ash (FA) are waste products from acetylene gas factories and power plants, respectively. The mixture of CCR and FA can produce a cementitious material because CCR contains a large amount of Ca(OH)₂ while FA is a pozzolanic material. Soil stabilization by CCR is classified using three zones: active, inert and deterioration. In the active zone, the natural pozzolanic material in the soil is adequate to produce a pozzolanic reaction. Hence, the input of FA into this zone does not significantly improve strength. Strength in the inert zone can be significantly increased by adding FA. FA improves the densification and pozzolanic reaction. The deterioration zone is not recommended for use in practice, even with the input of FA. The unsoundness due to free lime hinders strength development. Although the soaked and unsoaked strengths depend mainly on the CCR and FA contents, most of the ratios of soaked strength to unsoaked strength vary between 0.45 and 0.65. It is proved that a mixture of CCR and FA can be used for soil stabilization instead of ordinary Portland cement. The possible mechanism regarding the control of strength development presented in this paper can be applied to other clayey soils stabilized with different cementitious materials produced from Ca(OH)₂-rich and pozzolanic materials. This putative mechanism is also fundamental for further studies involving the development of rational dosage methodologies.