Improving hydrophobicity of asphalt surfaces using pulverized recycled polyethylene terephthalate: Towards efficient roofing/waterproofing

Abstract

Hydrophobic surfaces exhibit low wettability, low water and ice adhesion, etc. with an enhanced water resistance overall. Asphalt binder is popularly employed for roofing and waterproofing due to its intrinsic hydrophobicity. Yet, both unmodified and conventionally polymer-modified asphalt binders exhibit water contact angle (WCA) within the lower hydrophobic range (≤ 121°). Recent studies have shown that the hydrophobicity of asphalt binder can be enhanced via surface treatment using carefully selected materials. In this current study, the use of recycled polyethylene terephthalate (rPET) to improve the hydrophobicity of asphalt-binder was explored. The rPET was processed into micro-sizes and utilized to thermally treat the asphalt-binder at 100 °C. The morphology of the processed rPET and the treated-asphalt surfaces was examined using scanning electron microscopy (SEM). An optical surface profilometer was employed to quantify the roughness of the treated-asphalts. A video contact angle measurement system was used to measure the WCA of the unprocessed/untreated materials and the treated asphalt surfaces. The treated-asphalt showed average and maximum WCA of up to 144° and 148° respectively. This indicates that the rPET-treated asphalt surface could exhibit super-hydrophobicity (WCA ≥ 145°). The improvement in the WCA was due to the increase in surface roughness as a result of the embedment of rPET-particles onto the asphalt surface. The embedment resulted in the stretching of the asphalt surface, forming micro-valleys and -ridges of multiple hierarchies. Higher curing duration was found to yield treated-asphalts with hydrophobicity that last longer. It is found that micronized rPET with sizes smaller than 149 µm can be employed to successfully improve the hydrophobicity of asphalt binder surfaces.