An experimental study on the influence of metakaolin on mechanical properties of a clayey sand

The aim of this research is to investigate the effect of the additive metakaolin on the strength parameters of clayey sand soil. For this purpose, in addition to identification tests, a set of experiments including Atterberg limits and modified Proctor, uniaxial compressive strength, direct shear, permeability, and pH tests have been performed on some samples of the clayey sand soil under non-stabilized and stabilized conditions for different percentages of metakaolin. Furthermore, scanning electron microscopy (SEM) and X-ray diffraction (XRD) have been performed to investigate the microstructure of the non-stabilized and stabilized soil. The results showed that the maximum extent of increase in the strength occurred by metakaolin 25% and after 28 days of curing. Furthermore, elevation of the weight percentage of metakaolin in clayey sand soil causes to increase shear strength, diminish hydraulic conductivity, reduce the maximum specific dry weight of soil, and increase optimal water content, but it has a minor effect on pH value during the curing time. Investigation of the results obtained from XRD of the sample treated with metakaolin indicated the emergence of the cement compound called calcium silicate hydrate (CSH). Furthermore, the results of SEM imaging indicated that with the addition of metakaolin, the dispersed structure of soil changes into a flocculated structure, thereby enhances the soil strength.