Volume 35, Issue 6 (November 2007)
Using Rolling Dynamic Deflectometer and Overlay Tester to Determine the Reflective Cracking Potential
A forensic study was performed using a rolling dynamic deflectometer (RDD) and overlay tester (OT) to investigate the reflective cracks on SH87. Comparative tests were performed on the BU90 that has no cracks. The test results show that BU90 has lower density and lower asphalt content than SH87. This means the hot-mix asphalt (HMA) on BU90 has less resistance to reflective cracking than SH87. The OT confirmed that the cycles to failure are less for BU90 than for SH87. Thus, in terms of individual layer properties, the wearing surface and crack-retarding layer on SH87 has a greater crack resistance than that on BU90 and the asphalt mixes were not the principal reason for the cracking. The three main contributing factors for the reflective cracking on SH87 are: (1) thinner HMA, (2) higher joint movements, and (3) poor bonding between layers. Based on the reliability concept, at 90 % confidence level, the threshold W1–W3 deflection values were found to be 4.4 mils and it is much less than 6.5 mils developed from the IH20 project that has 100 mm of HMA as opposed to 64 mm for the SH87 project. It reaffirms that thicker HMA takes longer to have reflective cracking and it also needs a higher threshold W1–W3 deflection value. Thus, the thicker HMA overlay on BU90 (183 mm) would delay the reflective cracks. The methodology presented demonstrates RDD and OT’s abilities to characterize the reflective cracking potential and the proposed threshold value provides a good foundation for further refinement when additional data are available.