Strength and Stiffness of Cement Modified Clays
Author:
Alexander MotznyMentor:
Binod Tiwari, Assistant Professor, California State University FullertonConstructing civil engineering structures such as buildings and bridges on soft clays is always a challenge. This is mainly due to a heavy construction cost and risk of failure during seismic events. If the strength and stiffness of soil can be improved with admixtures such as cement and lime, construction cost can be significantly reduced. However, the effectiveness of such admixtures depends on the type of clay and its cation exchange capacity. In this study, two different types of clay minerals – kaolinite and montmorillonite as well as a natural soil from CSU Fullerton construction site were mixed with different proportion of Portland cement to evaluate the most appropriate proportion of cement that gives the highest strength and stiffness. Kaolinite is considered as preferable clay compared to montmorillonite for construction application. The compaction characteristics, shear strength and stiffness of the soil-cement mixtures were measured with a Harvard Miniature Compaction Device and a Unconfined Compression Testing Device. Based on the test results, the maximum dry unit weight/density of soil was obtained at 10% cement mixture by weight. Likewise, maximum unconfined compressive strength and stiffness also increases at 10% cement mixture. When the soil cement mixture was cured at moist condition for 14 days, the strength of the soil in all cases increased at least by 2 times. This clearly shows that while modifying the soil with cement in the field, it is better to allow the soil to gain strength by curing effect for at least a couple of weeks before putting a load on it.