Internal structure changes within porous asphalt mixture with different saturation under vertical repeated load

Abstract

Porous asphalt (PA) pavement is subjected to the coupling effects of vehicle load, high temperature and moisture saturation during rainy summer days. The harsh traffic and environmental conditions pose a great challenge to the longevity of PA pavement, which still lacks quantitative evidence. This study aims to characterize the internal structure change of PA mixtures under the actual coupling conditions through a modified dynamic creep test, in which the temperature of rainfall is realized through constant temperature water tank during repeated loading process. The microstructure changes of PA mixtures were characterized using image processing and analysis methods. The test results show that the influence of water saturation on permanent deformation is obvious in the compaction stage. At this stage, the creep rate of the saturated specimen is the highest, followed by the scoured specimen and dry specimen. The greater the degree of water saturation, the earlier the void area stops decreasing. The presence of moisture aggravates the occurrence of failure, and leads to an increase in the number of small voids. In addition, it is also found that the increase of water saturation will expand the influence range of load compaction, resulting in the difference in void area between upper and lower parts of PA-13 decrease. The difference in the number of small voids between upper and lower parts of PA-13 is also reduced. The greater the degree of water saturation, the more obvious the decrease of contact length at the initial stage of loading, which could be attributed to the increase of water saturation that promotes the filling failure at the initial stage of loading and leads to rheological failure and overpressure failure in advance. Moreover, the division of the change process of void area, quantity, and contact length are consistent with the permanent deformation. The findings of this study reveal important information about the damage evolution of PA pavement rutting resistance under different saturation states.