Time-dependent hydrophobic characterisation of granular materials synthesised with commercial chemical agents

Abstract

The impact of hydrophobicity on unsaturated granular materials is important because suction is a function of the degree of saturation as well as the surface tension and contact angle of the water menisci. In this study, coatings have been applied on the surfaces of a quartzitic sand at different concentrations following synthesis with eight commercial chemical agents and dimethyldichlorosilane (DMDCS) to induce hydrophobicity. Contact angle (CA) measurements and water drop penetration time (WDPT) tests have been carried out at different time intervals to investigate the hydrophobicity and its persistence. Scanning electron microscope (SEM)-energy dispersive X-ray spectroscopy (EDS) was performed to evaluate the resulting chemical composition of the sand. Results demonstrate that synthesis at high concentration (5%) caused fluctuations in CA and WDPT measurements within the first 24h. Except for one commercial chemical agent, the maximum CAs reached by the remaining agents after 24h were comparable to DMDCS (CA=119°). However, the critical concentration needed to achieve these CAs differed significantly: the lowest critical concentration amongst the commercial chemical agents was 0.2% whereas with DMDCS, the critical concentration was 0.0053%. The resulting surface properties of the synthesised granular materials with the commercial chemical agents showed increases in carbon content whereas with DMDCS, no change was recorded compared to the untreated sand. In addition to illustrating the efficacy of commercial chemical agents in inducing hydrophobicity in granular materials, this study has provided insights into the timedependent hydrophobic behaviour of granular materials following synthesis.