The effect of expanded perlite and metakaolin on the physicochemical properties of collapsible soils

Collapsible soils, such as loess, are a kind of problematic soil that is naturally unsaturated and withstands high loads at their natural moisture content, but unexpectedly collapses when wet and saturated, creating a risk to buildings constructed on it. This study highlights the effect of chemical stabilizers, including perlite and metakaolin, on the physicochemical behavior of collapsible soils, especially Zeta potential measurement, and the soil’s morphology. The properties of natural soil were compared to those of treated soil using a set of Zeta potential measurement tests. Furthermore, scanning electron microscopy (SEM) analysis was used to validate the results. According to the results, perlite and metakaolin changed the loess soil properties. The results showed that the absolute Zeta potential of soils increased after adding perlite and metakaolin, which indicated a higher dispersity of soils mixed with perlite or metakaolin. The scanning electron microscope (SEM) indicated that untreated samples had a loose structure with extensive pores, whereas treated samples had a dense and uniform structure with particle rearrangement. The flocculation and agglomerations in the soil matrix, which are a significant contributing factor to the mechanical property enhancement of the metakaolin-stabilized samples, were confirmed by SEM images. According to the microstructure and product composition analyses, the calcium-aluminate-silicate hydrate (CASH) generated by the metakaolin enhanced cementation between the flake units of the plain soil, and the soil structure of the plain soil stabilized by the metakaolin was denser.