Effects of Natural-Zeolite Additive on Mechanical and Physicochemical Properties of Clayey Soils

Modifying oil behavior with the help of additives is a superficial and deep soil improvement method. The considerable geological distribution of different types of pozzolanic materials, especially of zeolite in Iran, on the one hand, and the unique characteristics of these materials on the other, have caused this type of additive to be of interest to geotechnical engineers. In this study, in order to investigate the effect of zeolite on sandy clay soil and clayey sand soil, a set of tests including Atterberg limits, modified compaction, uniaxial compressive strength, and direct shear tests have been conducted. Further, scanning electron microscopy (SEM) and X-ray diffraction (XRD) have been performed to investigate the microstructure of stabilized and nonstabilized soil. The results indicated changes in Atterberg limits, internal friction angle, and maximum dry unit weight in response to alteration of the additive percentage. Further, changes in the zeolite percentage and curing time led to altered uniaxial strength of soil. With the increase in the percentage of zeolite and lengthening the curing time, the uniaxial compressive strength of samples increased, with the uniaxial compressive strength in clayey sand and sandy clay soil growing by 4 and 2.5 times the initial strength of soil, respectively. Thus, the effect of these additives is more considerable on clayey sand soil. In addition, the strength parameters of soil (including cohesion and internal friction angle) improved in response to adding zeolite. The maximum increase in the internal friction angle and cohesion was related to zeolite 25%. The results of XRD and SEM analyses indicated that stabilization with zeolite caused occurrence of chemical reactions and production of cement products including calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH), which is one of the main reasons behind the increased soil strength.