Soil Stabilization by Calcium Carbide Residue and Fly Ash

Calcium carbide residue (CCR) and fly ash (FA) are both waste products from acetylene gas factories and power plants, respectively. The mixture of CCR and FA produces a cementitious material because CCR contains a lot of Ca(OH)(2), while FA is a pozzolanic material. This paper investigates the possibility of using this cementitious material (a mixture of CCR and FA) to improve the strength of problematic silty clay in northeast Thailand. The influential factors involved in this study are water content, binder content, CCR: FA ratio, and curing time. The mechanism controlling the development of strength is also illustrated. Strength development is investigated using the unconfined compression test. A microstructural study using a scanning electron microscope and thermal gravity analysis is performed to understand the microstructural changes that accompany the influential factors. Both strength and microstructural investigations reveal that the input of CCR reduces specific gravity and soil plasticity; thus, the maximum dry unit weight and water sensitivity. The maximum strength of the stabilized silty clay occurs at approximately the optimum water content for different binder contents, CCR: FA ratios, and curing times. The improvement in strength for a particular curing time is classified into three zones: active, inert, and deterioration. In the active zone, the strength increases remarkably with the CCR content for all CCR: FA ratios. The input of FA (CCR replacement) does not significantly enhance strength development because all input Ca(OH)(2) is consumed by the natural pozzolanic material in the soil in the pozzolanic reaction. This active zone can be determined from the CCR fixation point, which is simply obtained from the index test. The input of FA (CCR replacement) is effective when the CCR content is in excess of the active zone, where insufficient natural pozzolanic material in the soil is present to react with the Ca(OH)(2). The possible mechanism controlling strength development that is presented in this paper can be applied to the other clayey soils stabilized with different cementitious materials, produced from Ca(OH)(2)-rich materials and pozzolanic materials, to explain and analyze strength development. Further study on a development of rational dosage methodology will be fundamental. DOI: 10.1061/(ASCE)MT.1943-5533.0000370. (C) 2012 American Society of Civil Engineers.