Factors Affecting Mortar Thickness Distribution and Its Relationship to Cracking Resistance of Asphalt Mixtures

This study introduces a novel method to determine the asphalt mortar thickness distribution through two-dimensional image processing techniques. It is claimed that in asphalt mixture design, there exists a potential optimal mortar thickness distribution, which can be used as metrics for quality control of durability. Gradation analysis from images was performed to verify the reliability of the analysis based on known gradation curve of mixtures and potential limitations for analysis are introduced. Image-based calculated gradation of asphalt mixtures is compared with gradation calculated from sieve analysis to verify accurate propotions of mixtures from images. Mixtures produced with modified and unmodified asphalt binders were utilized to compare the mortar distribution and the analysis of results is provided. In addition, three compaction temperatures were selected to investigate the temperature influence on mortar thickness distribution. The results indicate that there could be significant effects of binder modification and compaction temperature on mortar thickness distribution. Furthermore, the relationship between the mortar thickness distribution and the cracking resistance from the Semi-Circular-Bend test were analyzed. The relationships obtained verify that thinner mortar thickness, with a wider distribution, could cause the asphalt mixture to be more sensitive to aging, which is detrimental to the durability of the mixtures. The method used can be utilized for better mixture design and quality control to optimize binder content and durability.