The void characteristics of cement emulsified bitumen mixture under microwave heating by X-ray computed tomography

Abstract

Excessive void content is an essential reason for the poor road performance of cement emulsified bitumen mixture (CEBM), while incorporating steel slag with high microwave responsiveness into CEBM and followed by microwave heating may be an effective method to reduce void content. To verify this hypothesis, this paper investigated the effect of microwave heating on the void characteristics of CEBM using X-ray computed tomography. The study mainly focused on the distribution characteristics of different-sized voids, the distribution uniformity of voids, and the shape characteristics of voids. The results revealed that the number of different-sized voids decreased significantly after microwave heating, especially the number of small-sized voids decreased the most. The reduction in void number improved the distribution uniformity of longitudinal and radial voids. However, it reduced the distribution uniformity of voids between the inner and outer sections of the specimen. Through the analysis of aggregate movement characteristics, it was found that the increase in the separation degree of inner and outer voids was due to the larger-sized aggregates being more efficiently distributed on the outer section of the specimen. Additionally, microwave heating reduced the complexity of void shapes. The reduction of void number and the improvement of void characteristics by microwave heating are expected to enhance the structural durability of CEBM, thereby improving its road performance.