Thin epoxy overlays are used for improving the condition and extending the service life of bridge decks. The tensile bond pull-off strength, evaluated as per the ASTM C1583, is used as the performance indicator. A failure in the substrate with a tensile strength of 250 psi or greater is considered acceptable. However, the performance evaluated on in-service bridge decks shows inconsistent results. Laboratory studies by several researchers documented a distinct performance difference when the overlays are exposed to room temperatures in comparison to elevated temperatures. However, the most influential parameters such as concrete surface profile, thermal compatibility between overlay and concrete, the variation of substrate moisture against temperature, epoxy softening, and mechanical and interface epoxy properties under elevated temperatures were not measured and correlated to the observed performance. The performance of a concrete-overlay system depends on the mechanical and interface properties of epoxy, concrete surface profile, concrete properties, and exposure conditions. This study included experimental and numerical investigations to provide clarifications to the observed performance differences by evaluating the impact of concrete age at the time of epoxy application, concrete mix ingredients, exposure conditions, concrete microstructure development, substrate moisture and temperature, concrete surface profile, and epoxy properties on the performance of two epoxy overlays. Experimental results confirm that (i) the performance of epoxy overlays improves when the concrete mix contains slag and (ii) substrate moisture vapor pressure and epoxy softening under elevated temperature negatively affect the overlay performance. The concrete/epoxy bond interface undergoes higher degradation when subjected to an elevated temperature. The results obtained from the numerical analyses indicate a concrete surface profile of 6-8 with a height-space ratio of surface irregularities of 0.45 provides the maximum bond capacity for a thin epoxy overlay on a concrete mix with 35% slag and 65% Type I cement.