Ultra-thin whitetopping (UTW) is an alternative pavement rehabilitation option to asphalt concrete overlays. UTW is typically a concrete overlay less than 5 inches thick on an existing distressed asphalt pavement. A research project was recently finished to refine the current UTW design methods and develop new recommendations for improved UTW performance. As part of this project, a laboratory study investigated various concrete mixture effects on UTW performance. Seven mixture designs containing various w/cm ratios, cementitious content, discrete fiber-reinforcement content, and two coarse aggregate types were studied. A composite beam test (concrete placed on an existing asphalt beam) was developed to predict the composite section behavior in the laboratory. For this small-scale 2D testing, the results were not as dramatic as expected between the different concrete mixtures. However, the fiber-reinforcement, which increased the total fracture energy of concrete, demonstrated improvement in the load carrying capacity after initial cracking. The concrete mixture design alone was not the sole indicator of the UTW performance. Higher strength concrete mixtures can fracture just as rapidly as normal strength concrete if the UTW exhibits debonding. It is recommended that structural fibers be added to the concrete to extend the performance life of the rehabilitated pavement, especially in the presence of existing asphalt cracks and potential interface debonding.