Experimental Investigations on the Mechanical and Microscopic Behavior of Cement-Treated Clay Modified by Nano-MgO and Fibers

Abstract

Cement is often used to stabilize soft clay; however, it has some limitations in increasing clay strength and improving clay failure mode. To solve this, two different additives, i.e., polypropylene fiber and nano-Magnesium Oxide (MgO), were tested with the purpose of improving the mechanical performance of cement-treated soft clay. Four groups of samples with different mixture ratios of coastal soft clay, cement, fiber, and nano-MgO were first designed. Microscopy tests including X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS), as well as unconfined compression test was then carried out. XRD and EDS test results show that the cement hydration reaction is the main source of strength increase and the nano-MgO can generate Magnesium Silicate Hydrates (M-S-H) gelation, which helps to fill the pores of the clay and increase clay compactness. The unconfined compressive strength test results show that adding fiber or nano-MgO alone has a poor effect on the strength improvement for cement-treated clay with high water content. However, adding both additives lead to a significant increase in the clay’s unconfined compressive strength, which is verified by the microscopic observation of clay compactness in SEM images. Moreover, the fiber is found to increase the ductility of cement-treated clay based on the observed failure modes of modified samples.