Shearing behaviour of silty clay stabilized with calcium carbide residue: Strength and microstructural evaluations

Since clayey soils contain a large amount of natural Pozzolanic materials, calcium carbide residue (CCR) material can be used as a stabilizer to improve their strength. In this research we conducted a total of 60 direct shear tests, to evaluate the shear behavior of the CCR-stabilized clay soil. In tests, the variable parameters were CCR contents (3%, 7%, 10% and 13%), curing times (CT) (7, 14, 28 and 60 days) and vertical stress values (0.50, 1.00 and 1.50 kg/cm 2 ). Also some microstructural analysis was performed in clayey soil, CCR and the CCR-clay soil mixture to study the variation microstructural of this combination. To evaluate the shear behavior of the soil, the effect of the CCR and CT on the important parameters such as improvement factor (IF), cohesion (c) and internal friction angle (φ) of the soil has been investigated. The results showed that by adding the CCR to the natural CL-ML soil increases shear stress (τ), shear strain, c, φ and plasticity of the soil. At CT=28 days, adding the 3% CCR to clayey soil caused increasing 422% and 22% in the c and φ values, respectively. The results demonstrated that the CCR and CT variations are more effective on c values rather than φ values. Microstructural analysis demonstrated that adding CCR to clayey soil and CT=28 days decreases crystalline phases, increases amorphous phases, and forms secondary products. The findings of this research indicate that the use of the CCR as a waste material can be used in the stabilization of fine-grained soils in road construction, which causes a significant increase in the shear strength of the soil and a significant reduction in the emission of carbon dioxide in nature.