Effects of Silica Fume and Nano-silica on the Engineering Properties of Kaolinite Clay

The improvement of geotechnical properties of weak soils is of interest through the resources shortage. Therefore, this study focused on the effect of silica fume as industrial waste products and nano-silica on geotechnical characteristics and micro-structural properties of kaolinite clay as a soft soil with poor strength properties. Silica fume was added to the kaolinite clay to enhance the strength with 5, 10 and 15%. Moreover stabilized soil with nano-silica were fabricated with 1, 2 and 3% by dry weight of the soil. Then, Atterberg limits, standard proctor, unconfined compressive strength, and California bearing ratio tests were conducted. In addition, the micro-structural changes of soil samples through the stabilization were examined using scanning electron microscope. The results indicated that silica fume and nano-silica increase the optimum water content and decrease the maximum dry density of the stabilized soils. Addition of 15% silica fume and 3% nano-silica to kaolinite clay improved the unconfined compressive strength at curing age of 28 days by up to 70% and 55%, respectively. Also, the results of soaked California bearing ratio test after 7 days of curing demonstrated that 15% of silica fume and 3% nano-silica increased the California bearing ratio values about two times more than the raw soil. Scanning electron microscope (SEM) images were then utilized to evaluate the effects of additives on the kaolinite clay soil. It was concluded that silica fume and nano-silica filled pore space between clay particles and a dense matrix were formed. This textural event caused an improvement in compressive strength of stabilized soils.