Sustainable stabilization of fiber-reinforced clayey sand using zeolite as partial cement replacement

Clayey sand soils require improvement in civil engineering projects due to their low density, high porosity, and inadequate shear behavior. On the other hand, the extensive use of cement in soil stabilization is associated with environmental concerns such as high CO₂ emissions. In this study, the effect of partial replacement of cement with zeolite (up to 50 %) and the addition of polyvinyl alcohol (PVA) fibers (up to 0.8 wt%) on improving the mechanical, microstructural and environmental properties of clayey sand soil was investigated. Samples were prepared with different cement contents (3 and 6 %) and, after 7 and 28 days of curing, were subjected to compaction, unconfined compressive strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity (UPV), scanning electron microscope (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and toxicity characteristic leaching procedure (TCLP) tests. The compaction test results showed that maximum dry density (MDD) decreases and optimum moisture content (OMC) increases with increasing zeolite content. The performance of different mixtures showed that the optimum mixture consisted of 6 % cement, 20 % zeolite, and 0.8 % fibers, which increased UCS, ITS, and UPV by 320 %, 194 %, and 35 %, respectively, compared to unstabilized soil. Microstructural analyses showed the formation of CSH and CAH gels and improved interfacial transition zone bonds. Also, TCLP results showed that zeolite reduced heavy metal leaching. This study, with an innovative approach, investigated the simultaneous effectiveness of zeolite, cement, and fibers and introduced the potential of the UPV method as a non-destructive method for evaluating the mechanical performance of stabilized soil.