Effects of overlay thickness on surface cracking and debonding in bonded concrete overlays

The performance of bonded concrete overlays can be diminished by early age surface cracking and (or) debonding at the interface between old and new concrete. This early age failure can be attributed to the volume changes of the overlay concrete caused by shrinkage and temperature change. An experimental program was conducted to understand the effects of overlay thickness on the early age failure of bonded concrete overlays. A finite element model was developed to assess stress development and debonding behavior due to volume changes for various overlay thicknesses. The experimental measurements and numerical analysis demonstrated that overlay surface cracking and debonding at the interface are interdependent in thin overlays. To prevent premature surface cracking, a minimum overlay thickness should be determined based on the shrinkage and thermal changes of overlay concrete, and construction practices should be selected to mitigate the shrinkage and thermal gradient through the overlay thickness.