Enhanced stabilization of highly expansive clays by mixing cement and silica fume

The present study investigated the potential use and effectiveness of expansive clay stabilization using a mixture of cement and silica fume (CSF) as a possibly useful option from environmental, economic, and (or) technical perspectives. In so doing, cement and CSF blend with 10% cement replacement were separately added to a clay sample having high degree of swelling potential, and then, a set of macro and micro level tests were performed under various curing regimes to assess the responses of amendments. The results showed that at ambient condition of 20 °C, highly expansive clays need a large quantity of cement (≥ 15%) and a curing time of 28 days to get stabilized satisfactorily. In this case, although a higher temperature (40 °C) leads to a decrease in the required time of curing, there is no a remarkable reduction in the optimum content of additive. It appeared that the CSF binary system can expedite the process of stabilization and thus is more efficient in improving the clay engineering properties with a lower amount of binder (to about 33%) and shorter curing ages (by nearly 2 times) compared to the sole cement. In fact, based on the XRD and SEM analyses, the incorporation of silica fume into the cement matrix extends the formation of new cementing compounds and provides a much denser microstructure; two features which were found to be very effective in surpassing the problems associated with expansive clays.