Laboratory evaluation of performance of porous ultra-thin overlay

Porous ultra-thin overlay (PUTO) is a new type of pavement maintenance technology which combines skid resistance and drainage functions. The engineering properties of two high-viscosity modifier (type I and type II) modified asphalt and two gradations (coarse and fine) of asphalt mixtures, including high- temperature rutting resistance, low-temperature crack resistance and moisture sensitivity, were investigated. The dynamic modulus and phase angle of the asphalt mixture under dynamic loading conditions were then analyzed and master curves of dynamic modulus and phase angle were established. Finally, the drainage and skid resistance of the PUTO were evaluated. The results show that the dynamic stability (DS) of the asphalt mixture with coarse gradation is larger than that of the asphalt mixture with fine gradation. The bending strain of four asphalt mixtures shows small differences, the maximum value being 364 με larger than the minimum value, and they all meet the requirements of the specification. The excellent adhesion of the high-viscosity asphalt binder enhances the anti-stripping ability between asphalt and aggregates, enabling the mixture to resist water damage well. As the temperature increases or the load frequency decreases, the dynamic modulus decreases and the phase angle increases. By establishing the master curves of dynamic modulus and phase angle, it can be concluded that gradation as the main skeleton of PUTO asphalt mixture plays a major role in its performance and strength. Under the same rainfall conditions, the asphalt mixture with coarse gradation can transfer water on the pavement surface to the outside more quickly. Coarse gradation is beneficial for the enhancement of the macroscopic structure and improvement of the skid resistance of pavement surface.