Random distribution of asphalt and cement mortar in semi-flexible pavement: Implication for cracking resistance

The distribution characteristics of asphalt and cement mortar play a crucial role in determining the cracking resistance of semi-flexible pavements (SFP). In this study, digital image processing technology was utilized to quantify the thickness distribution of asphalt and cement mortar within SFP, and a parallel line segmentation method was employed to characterize the random distribution of mortar thickness (RDMT) of asphalt and cement mortar. Variance, coefficient of variation (COV), and interquartile range were proposed to characterize RDMT, examining the effects of air voids (AV) content, nominal maximum aggregate size (NMAS), and compaction method on RDMT, and its variation along the specimen height. Semi-circular bending test was conducted to evaluated the cracking resistance of SFP, exploring the relationship between RDMT and cracking resistance. Results indicate that parallel line segmentation method with 36 parts and 25 parts is recommended to characterize the RDMT of asphalt and cement mortar, respectively. An increase in AV content led to a higher RDMT for asphalt mortar but a lower RDMT for cement mortar. Conversely, as NMAS increased, the average thickness of asphalt and cement mortar increased, while the RDMT of asphalt mortar decreased and that of cement mortar increased. RDMT of asphalt and cement mortar is higher under Superpave gyration compaction method compared to the Marshall compaction method. Additionally, RDMT increased from the top to the bottom of the specimen height. Based on the RDMT, a random distribution index (RDI) was proposed, which exhibited a strong linear relationship with the cracking resistance of SFP. When the RDI decreased by 44.4 %, the corresponding cracking resistance of SFP increased by 84.0 %. Improving the distribution of asphalt and cement mortar could enhance the cracking resistance of SFP.