Approximately 45 percent of the New Jersey Department of Transportation’s (NJDOT) roadways are composite (hot mix asphalt overlying Portland cement concrete). Hot mix asphalt (HMA) is used as the overlying material because of its inexpensive nature when compared to most PCC rehabilitation/reconstruction alternatives. In addition to being economical, HMA also allows faster repairs resulting in shorter construction duration and lower “User” delay costs. However, due to the majority of the PCC pavements being in average to poor condition, many HMA overlays are exposed to extreme movements (both vertical and horizontal). The combination of associated load and environmentally induced movements creates complex stresses and strains in the vicinity of expansion joints and cracks in the PCC, thus dramatically reducing the life of the HMA overlay, typically in the form of reflective cracking. It should be noted that there currently does not exist an AASHTO accepted pavement design method for the pavement design of composite pavements.

A research project was undertaken to evaluate how the NJDOT can optimize the use of hot mix asphalt overlays when rehabilitating PCC/composite pavements. Field test sections were evaluated and instrumented to measure the PCC joint movements and pavement specific traffic conditions. Asphalt mixtures placed on the test sections were sampled and evaluated under laboratory tests that model field movements and conditions. The collected field and laboratory data, as well as collected Literature Review information and National Survey information, provided valuable information used to develop an asphalt mixture design and selection procedure for the NJDOT. The procedure was able to predict the early (only 2 years of service life was available for comparison) reflective cracking, as determined by the percent of PCC joints cracked, to within 9% of the measured values.