RDD Data Interpretation and Its Application on Evaluating Concrete Pavements for Asphalt Overlays

The placement of an asphalt overlay is the most common method to rehabilitate existing concrete pavements. Reflective cracking, however, has been a serious problem with asphalt overlays for a long time. To prevent reflective cracking, it is critical to evaluate existing concrete pavements and identify the joints/cracks with poor load-transfer efficiency (LTE) before placing an asphalt overlay. The most common equipment for this evaluation is a falling weight deflectometer (FWD). However, FWD testing is conducted only at discrete points and is time consuming. It is desirable to use the rolling dynamic deflectometer (RDD) that can continuously characterize each slab and all joints and cracks (e.g., LTE). The RDD was developed in the 1990s at the Center for Transportation Research in Austin, Texas. The RDD is one of the few operational rolling deflection systems that provide continuous data to make project level decisions on rehabilitating concrete pavements. In contrast to the FWD, no RDD data analysis software is available. This paper discusses RDD data interpretation and its application on evaluating existing concrete pavement for asphalt overlays. First of all, some basics of RDD deflection data interpretation are discussed. Several common patterns within the RDD data are identified, and associated interpretation and limited verification are presented in this paper. The RDD deflection data measured before an asphalt overlay on Interstate Highway-20, Texas, and the observed asphalt overlay performance (in terms of reflective cracking) are then presented, and the relationship between RDD deflection and reflective cracking rate is further investigated. Finally, guidelines for evaluating existing concrete pavements using RDD are proposed.