Threshold values for reflective cracking based on continuous deflection measurements

The fundamental mechanisms leading to the development of reflective cracking are differential movements from the supporting pavement structure. In this Study, the deflection profiles collected using the rolling dynamic deflectometer (RDD) were used to determine the threshold values for reflective cracking. This provides a quantitative method to determine the severity of the cracks (or joints), which controls the potential for reflective cracking. Three different deflection parameters were considered: (i) sensor 1 deflection (W1), (ii) differential deflection between sensor 1 and sensor 3 (W1-W3), and (iii) multiple of baseline deflection value. The reliability concept was also incorporated such that pavement engineers can select criteria (based on predefined confidence levels) to identify locations where reflective cracking is likely to take place. Threshold values were determined from a 4 year study conducted along US Interstate Highway 20 (IH-20), and case studies from overlay projects along State Highway 73 (SH-73) and US Highway 59 (US-59) were investigated to verify the proposed threshold values. Based on the findings in this study, the RDD can identify problematic areas but can also be used to optimize the rehabilitation strategy. As evident from the SH-73 and US-59 projects, the W1-W3 deflection and 2.5x baseline deflection are better criteria than W1 deflection alone.