Permeability and compressibility of wax-coated sands

Wax-coated sands are synthetic soils that have the potential to generate many new geotechnical applications in addition to synthetic horseracing tracks and sport fields. Compared to natural sands, wax-coated sands are hydrophobic and display superior, but not yet well-understood, mechanical and hydraulic properties. Based on a series of laboratory tests, this study investigates the effects of wax content on the permeability and compressibility of wax-coated sand. Laboratory results show that wax contents up to 6% may triple permeability and double compressibility. Simplified physical models are developed to analyse the experimental results and describe the effect of wax coating on permeability and compressibility. These models imply that the increase in permeability results from the aggregation of smaller sand particles caused by the wax tackiness, which generates larger interstices. The smaller particles attach to other particles and render the sand coarser. The wax coating also softens the contact between sand particles and makes the wax-coated sand more compressible. More research is warranted to explore the applications of hydrophobic coating in geotechnical engineering.