Water resistance and characteristics of asphalt surfaces treated with micronized-recycled-polypropylene waste: Super-hydrophobicity

Abstract

Research studies have shown that superhydrophobic (SH) surfaces possessed better and enhance water-resistance, anti-icing, anti-corrosion, and even self-cleansing properties than non-SH surfaces. Although asphalt binder is widely used for waterproofing and damp-proofing application, it was established that asphalt binder is only hydrophobic not SH. The potential use of micronized recycled-polypropylene (RPP) to boost the properties of the asphalt binder to SH has been examined in this study. Micronized RPP were obtained by milling and sieving of polypropylene plastic waste. Two different sizes of the micronized RPP (maximum size of 177 and 149 µm) were thermally fused on to the surface of asphalt substrates at 100 °C, for curing durations of 25, 40, and 55 min. Surface profile and water contact angle (WCA) of the RPP-treated asphalt substrates were evaluated using 3D profilometer and video contact angle measurements respectively. Surface morphology of the micronized RPP and the treated asphalt substrates was also examined using scanning electron microscope (SEM). RPP-treatment of the asphalt substrates resulted in their transformation from hydrophobic to SH WCA range. Highest improvement in average WCA of 156° from 110° (41.81% increase) was observed for substrate treated with micronized RPP having maximum size of 177 µm, and cured for 55 min. This corresponds to 86.81% drop in work of adhesion. The increase in WCA was found to be due to stretching and profile transformation of the asphalt substrates surface, which occur as a result of the RPP particles embedment. Statistical analysis showed that both the curing duration and size of the RPP have significant influence on the profile and the WCA of the treated asphalt substrates. Re-evaluation of the treated asphalt substrates after 12 months of exposure revealed that higher mass accumulation of the RPP on the asphalt surface yielded more stable WCA over time.