Experimental investigation on the durability of hydrophobized soils

Abstract

Hydrophobized soils are granular materials with a low affinity for water. Because the soils can delay water infiltration, there is an increasing interest in their potential use in infiltration barriers. Soils are hydrophobized by coating hydrophobic polymers onto the soil particle surfaces. It is hypothesized that such soils can degrade by particle breakage or the coating ageing. However, little is known on the long-term response of these new materials to the environment. This research aims to explore the degradation of hydrophobized soils under abrasion and weathering, in order to optimize their use in ground infrastructure. The specific objectives are to: (1) develop a soil hydrophobization method with Tung oil, a costeffective and sustainable material; (2) assess the ecotoxicity and potential environmental risks of hydrophobized soils; (3) evaluate the interaction effect between soil hydrophobicity and particle breakage during abrasion; (4) investigate the degradation of hydrophobized soils subjected to weathering and, (5) extend the lifespan of soil hydrophobicity by encapsulation methods. Soils were mixed with Tung oil and heated at different temperatures and durations to develop and optimize soil hydrophobicity. Tung oil induced severe and persistent hydrophobicity with heating, enhancing hydrophobicity until a critical temperature and duration threshold was reached. The results provide a sustainable and cost-effective soil hydrophobization method. The ecotoxicity and environmental risks of hydrophobized soils was assessed by biological assays and leachate tests respectively. Biological assays revealed minimal impact on soil microorganisms by hydrophobization. Total concentrations of heavy metals measured by leachate tests remained below the guidelines, indicating the leachate hazard will be negligible. The results demonstrate the environmental safety of hydrophobized soils as fill materials. The interaction effect between soil hydrophobicity and particle breakage was investigated by Micro-Deval abrasion tests. During abrasion both particle breakage and hydrophobicity reduction occurred. Hydrophobicity degradation was driven by the particle breakage, which was also affected by coating type and concentrations. To investigate the degradation under weathering, the soils were subjected to thermal ageing, water immersion, cyclic wetting-drying and cyclic freezingthawing. The results revealed declined hydrophobicity under thermal ageing and water immersion conditions, driven by oxidation of the hydrophobic coatings (thermal ageing) and hydrolysis (water immersion). Cyclic wetting-drying induced hydrolysis and detachment of coatings. Soil hydrophobicity was stable during freezing-thawing cycles. A proof-of-concept test was carried out to explore the use of encapsulation methods on soil hydrophobization. Preliminary results reveal that the release of hydrophobic cargos encapsulated in shells was triggered by shear stress or water flooding, which consequently hydrophobized the soils. This research sheds light on the understanding of the degradation behavior of hydrophobized soils, and therefore provides a basis for their long-term use in ground infrastructure.