Evaluation of high-temperature deformation of porous asphalt mixtures based on microstructure using X-ray computed tomography

Abstract

Porous asphalt (PA) mixtures are used as a surface layer experiences high temperatures and overloading in the summer in Southern China. The objective of this research is to characterize the microstructure evolution of PA mixtures under high-temperature deformation. The advanced repeated load permanent deformation (ARLPD) test is chosen to evaluate the rutting resistance and the test temperature is 55 °C. The loading process is divided into three stages based on a three-stage model, and X-ray CT is conducted on the specimen in the original state, prime stage, secondary stage, and tertiary stage. Air void regions are extracted in the CT slices. An algorithm is proposed to recognize the connecting air voids. Characteristics of air voids and connecting voids are obtained, including the air void contents, air void number, and air void equivalent diameter in the longitudinal and radial directions. The total air void content of the loading portion of the specimen decreased, increased, and decreased in the prime stage, secondary stage, and tertiary stage, respectively. It is worth noting that the total air void content declined in the tertiary stage; this may due to the fracture of aggregates, thus gap grading the high air void content in PA mixture. The irregular shape of the loaded specimen may lead to unreliable total air void contents by traditional methods. A more adaptable method would be helpful to obtain data from irregular specimens. The connectivity of PA mixture increases significantly and most air voids in the specimen are translated into connecting air voids.