ABSTRACT
Several challenges in ensuring an ultra-thin whitetopping (UTW) pavement meets the service life objective are preserving bond between the concrete and existing asphalt concrete layer, and maintaining adequate load transfer across the joints. Since no man-made load transfer devices exist across the contraction joints, the crack width or joint opening must be minimized to maintain aggregate interlock. Several ways to minimize joint opening include smaller slab sizes and selecting concrete mixtures with low heat of hydration, low drying shrinkage potential, or with the inclusion of fiber-reinforcement. Selection of a small slab size will only promote good load transfer if uniformly distributed working cracks exist at early ages. Several UTW projects completed at the University of Illinois in the summer of 2006 and 2007 (Roesler et al. 2008) indicated that many of the contraction joints did not crack initially. In fact, the initial joint cracks occurred at every 5 to 8 joints (for 4 × 4 ft panels). The result of this large crack spacing was wider openings at these initial crack locations and reduced load transfer. Cracks at other locations eventually propagated, but the load transfer efficiency (LTE) across these cracks were dramatically higher than the initial cracks.
