Long term bond strength and chloride resistance of epoxy and concrete overlays
There has been an increasing need to extend the service life of bridges due to deteriorating conditions of infrastructure and associated fiscal limitations. To protect bridge deck against deterioration, as well as to improve bridge performance through better maintenance practices, a better understanding of performance of the recently developed thin epoxy overlay and the well-adopted low slump dense concrete (LSDC) overlay is desired. To evaluate the performance of these two overlays, the following objectives are proposed: to evaluate the initial and long-term bond strength of overlays; to assess the chloride resistance of overlays and to identify factors that affect the initial performance of overlays. To fulfill these objectives, six existing bridges were chosen to install the two overlay types, and field inspections were performed on selected bridges to document substrate surface conditions; substrate cores were extracted and tested by both ASTM C642 and ASTM C666 to evaluate their porosity and durability to cyclic freezing condition; on-site pull-off tests (ASTM C1583) were conducted to assess the initial bond strength of overlays; laboratory pull-off tests (ASTM C1583) were conducted under cyclic freezing conditions to evaluate long-term bond strength and salt-ponding tests (AASHTO T259) were performed to assess chloride resistance.
The results from these testing efforts indicated that the initial bond strength of both overlays are good; the long-term bond strength of thin epoxy overlay decreased sharply after 300th F/T cycles, whereas the bond performance of the LSDC overlay remained unchanged; chloride resistance of the epoxy overlay is much better than LSDC overlay and the percentage of air voids of the substrate concrete was seen to have an effect on the initial performance of the overlays.