In recent years, ultra-thin whitetopping (UTW) has evolved as a viable rehabilitation technique for deteriorated asphalt cement concrete (ACC) pavement. Numerous UTW projects have been constructed and tested, enabling researchers to identify key elements responsible for the successful performance of UTW. These key elements include foundation support, interface bonding condition, portland cement concrete (PCC) thickness, synthetic fiber reinforcement usage, and joint spacing. The interface bonding condition is the most important of these elements because it enables the pavement to act as a composite structure, thus reducing tensile stress and allowing an ultra-thin PCC overlay to perform adequately. Although the key elements affecting UTW performance have been identified in previous research, neither the impact that external variables have on the elements nor the element interaction have been thoroughly investigated. The objective of this research was to investigate the interface bonding condition between an ultra-thin PCC overlay and an ACC base over time, considering the variables of ACC surface preparation, PCC thickness, synthetic fiber reinforcement usage, and joint spacing. Laboratory testing and full-scale field testing were used to accomplish the research objective. Laboratory testing involved monitoring interface strains in fabricated PCC/ACC composite beams subjected to either static or dynamic flexural loading. Variables investigated included ACC surface preparation, PCC thickness, and synthetic fiber reinforcement usage. Field testing involved monitoring interface strains and temperatures, falling weight deflectometer deflection responses, direct shear strengths, and distresses on a 7.2 mile Iowa Department of Transportation UTW project (HR-559). Variables investigated included ACC surface preparation, PCC thickness, synthetic fiber reinforcement usage, and joint spacing. The results of both laboratory and field testing are presented and summarized in this paper.