Hydrophobisation of clays and nano silica for ground engineering

Department of Civil Engineering, Haking Wong Building, The University of Hong Kong. Pokfulam Road, Hong Kong, China

^* e-mail: yunesh@connect.hku.hk lourenco@hku.hk

Abstract

Altering the hydrophobicity of particles allows their use as functional construction materials in ground engineering (e.g. in barriers). This study examines the hydrophobisation of nano to micro particles by using two clays (kaolin and halloysite) and nano silica. To induce hydrophobicity, dimethyldichlorosilane (DMDCS) was used in concentrations varying from 0.25% to 20%. The sessile drop method was used to measure the contact angle (CA) of the particles. Kaolin was initially hydrophobic with a CA of 93 5^◦ while the other two materials were hydrophilic. The addition of DMDCS to the materials increased CAs of all materials investigated. The maximum CAs recorded at 20% for the halloysite, kaolin and nano silica were respectively: 116 5^◦, 143 3^◦ and 144 6^◦. The difference in CAs attained by the clays was attributed to their different structure. Scanning electron microscope-energy dispersive spectroscopy analysis showed increases in carbon content with only halloysite and nano silica after hydrophobisation. The results demonstrate that hydrophobising clays and nano silica can effectively improve their resistance to water infiltration.