Modification Of Asphalt And Its Application In Porous Asphalt Mixture

Porous asphalt pavement, which possesses many advantages such as lowering noises, avoiding water splashes and glistens, reducing the city surface runoff, alleviating the city hot island effect and enhancing road surface adhesion, etc, is a novel and environment-friendly pavement structure and has been widely studied and applied in the abroad. The performance of the asphalt required in the porous asphalt pavement are quite high, especially the softening point and stickiness, which are higher than those in the ordinary asphalt concrete. The common asphalt must be modified before used in the porous asphalt mixture. At present, the investigation and application of the porous asphalt pavement in China are underway, and most techniques are introduced from the developed countries.In this paper, the performance requirements of the modified asphalt used in porous asphalt pavement in Hangzhou was proposed according to the climate circumstances and the results by analyzing the porous asphalt pavement constructed in Hangzhou, and referring to the literatures about the criteria of modified asphalt used in porous asphalt pavement at home and in abroad. Then modifications of asphalt by using SBS and crumb rubber were investigated and some performance criteria of the modified asphalt which can be fitted for porous asphalt pavement were suggested. And the road performance, such as permeability, Marshall stability and rut resistance of the porous asphalt mixture by using the modified asphalt are also investigated.The results showed that the highest temperature measured in the porous asphalt pavement in summer is 62.5℃, while it reached 67.9℃for ordinary asphalt pavement under Hangzhou climate circumstances. The heat conduction of porous asphalt pavement is better than that of ordinary asphalt pavement in the same climate. The effect of temperature-reducing of the pavement is more obvious for porous asphalt pavement. It has been suggested that the softening point of the modified asphalts used in the porous asphalt pavement should not be lower than 70℃, and the penetration should not be lower than 40 (0.1 mm), and the ductility should not be lower than 40 cm at 15℃or should not be lower than 6 cm at 5℃under Hangzhou climate circumstances. The softening point of the asphalt modified by using 4% SBS and 15% crumb rubber is about 72.6℃, the penetration is about 40.7 (0.1 mm), and the ductility at 5℃is 9.0 cm which can meet the requirements of the suggested criteria of the modified asphalt for the porous asphalt pavement. The optimum asphalt content in porous asphalt mixture by calculating originally asphalt content which based on theory of asphalt film thickness was confirmed by the Marshall and rut resistance experiments. And the dynamic stability measured were all over 1000 times/mm by using the standard rut experiment, rut experiment after being acted by load or rut experiment after being waterish-logged. The performances of the porous asphalt mixture produced by the modified asphalt are steady, and could meet the requirements of urban roads.