| In the long term,the wheel load causes secondary condensation of porous asphalt concrete pavement,and the redistribution of internal structure may reduce the drainage performance of the pavement.To track the failure process of the internal structure,the deterioration process should be investigated.This paper took muti-factors into consideration,which may affect the pavement during practical application,including load,temperature and water saturation.The wheel tracking test and dynamic creep test were produced to simulate the coupling effect of multi-factors.Highresolution scanning technology was used to track the deterioration process of mesoscopic structure of porous asphalt concrete under the coupling effect of multi-factors.The correlation of the permanent deformation parameters and mesoscopic parameters was analyzed.Firstly,the high-resolution scanner was used to obtain the two-dimensional image of asphalt concrete slice,and aggregate and air void of porous asphalt concrete were extracted by digital image processing.Based on the principle of the shortest contact distance,the thickness of mastic at each point of aggregate or void boundary was captured to quantify the distribution of mastic thickness.At the same time,by setting the contact threshold,the contact length of aggregate was captured to quantify the skeleton of asphalt concrete.Secondly,the wheel tracking test and immersion wheel tracking test were used to study the deterioration process of mesoscopic structure under different temperature.Based on slice image at different time,the permanent deformation area and the average rutting depth were calculated to analyze the difference of the permanent deformation in different test conditions.The loading process was divided into three durations(condensation,transition and stabilization)according to rutting depth rate.The aggregate movement process was calculated by the binary image of aggregate at different time,while the difference between the two types of rutting specimens was also compared to analyze the influence of the difference on the changing air void structure.The changing skeleton structure during wheel loading was evaluated by the change of contact length.The influence of environmental factors on the stability of skeleton structure was also studied.It has been found that the more worse test condition causes more serious damage of contact length at the early stage of test.The void area and small void number were used to evaluate the condensation degree of initial voids and failure accumulation at different time.It has been found that the rise of temperature could aggravate adhesion failure and the immersion condition could promote the condensation of the specimen.Thirdly,the simulated rainfall device was produced to achieve different water saturation,while the deterioration process of mesostructure was stuied under uniaxial loading.Based on the change of creep rate in each loading stage,the creep process was divided into three durations(condensation,transition and stabilization).The effect of water saturation on creep rate was mainly concentrated in the condensation duration.With the increase of water saturation,the time point of stop falling of contact length failure and void area were be ahead of time.Compared with the dry condition,the main effect of scour condition was to promote failure.The main effect of immersion condition was to weaken the stability of structure and promote the condensation of the specimen under load.Finally,the repeatable double factor variance analysis was used to verify the sensitivity of the mesostructure to the loading time(or times)and environment factors.The correlation between the permanent deformation parameters and the mesoscopic parameters were analyzed.The results show that under wheel tracking test,the relationship between contact length and permanent deformation increases with the rise of temperature,while void indices were reverse;under dynamic creep test,the relationship between contact length and permanent deformation increases with the increase of water saturation,while small void number was reverse. |
