Thin asphalt overlays are non-structural preventative maintenance (PM) mixes used for the routine maintenance and rehabilitation of existing pavements. They are typically placed in thin layer lifts of about 25 mm thick. Traditionally, thin overlay application is primarily used to preserve pavements exhibiting surface distresses such as raveling, ageing, bleeding, minor cracking, minor disintegration, texture loss, skid resistance loss, etc. Candidate pavements for thin overlays should generally be structurally sound with no major structural defects such as rutting or fatigue cracking; otherwise a thicker overlay or reconstruction is recommended (Technical Bulletin 2002). Rutting greater than 6.25 mm should be sealed and any surface deformities greater than 12.5 mm should be filled up (but not over filled) prior to overlay placement. Equally, potholes should be sealed and patched up, respectively (Uhimeyer 2003).
1.1 Thin HMA overlay application