Inducing hydrophobicity in saline soils: A comparison of hydrophobic agents and mechanisms

Hydrophobized soils (or so-called artificial hydrophobic soils) are a novel geomaterial with a great potential in engineering applications due to its low affinity to water. For saline soils, hydrophobizing such soils can mitigate the soil salinization and subsequent engineering disasters such as salt expansion and corrosion by chlorides. To induce soil hydrophobicity, hydrophobic agents are widely used such as organo-silanes, fatty acids, and waxes. Correspondingly, the engineering properties and durability of these hydrophobized soils have been comprehensively investigated. However, all these studies focused on the clean mineral soils, i.e., the soils without salts and in a moderate pH. For saline soils, the feasibility, stability and durability of these hydrophobic agents are unclear. This paper aims to propose suitable and feasible hydrophobic agents in hydrophobizing saline soils, by investigating its hydrophobicity change and having an insight into the mechanisms. The saline soils used were collected from Qinghai, China, and were treated by five different hydrophobic agents at different concentrations, with the hydrophobicity quantified by water drop penetration time, surface tension and contact angle. The soil hydrophobicity change was recorded after the treatment and wetting-drying cycles, in order to assess its stability and durability. Fourier transform infrared spectroscopy (FTIR), Raman spectrum and N2 adsorption experiment were carried out to study the mechanism of soil hydrophobicity formation and degradation. The results showed two agents, namely Sodium methyl siliconate and Polymethylhydrosiloxane, provided the greatest and most durable hydrophobicity in saline soils. Their different formation mechanisms at particle- and nano-scale were also discussed. A further assessment on the soil mechanical properties revealed that both compaction behavior and strength were negligibly influenced by these two agents.