Iowa Department of Transportation
Second Strategic Highway Research Program (SHRP2)
Kejin Wangkejinw@iastate.edu email >
PCC Engineer, CP Tech Center
Brent Pharesbphares@iastate.edu email >
Bridge Research Engineer, BEC
About the research
To improve long-term bridge performance through better design and maintenance practices, as well as to promote service life design (SLD) concepts, the Iowa Department of Transportation (DOT) has sought to implement SLD recommendations from two projects conducted under the Second Strategic Highway Research Program’s (SHRP2’s) Service Life Design for Bridges (R19A) in future bridge preservation practice.
The aim of the present study was to evaluate the bond strength and chloride resistance of thin epoxy overlays and compare the results with those obtained from low-slump dense concrete (LSDC) overlays. The following specific objectives were proposed: evaluate the initial and long-term bond strength of overlays, assess the chloride resistance of overlays, and identify the factors that affect the initial performance of overlays.
To fulfill these objectives, six existing bridges were chosen for installation of the two overlay types. Field inspections were performed on the selected bridges to document substrate surface conditions, substrate cores were extracted and tested using both ASTM C642 and ASTM C666 to evaluate the overlays’ porosity and durability to cyclic freezing conditions, on-site pull-off tests (ASTM C1583) were conducted to assess the initial bond strength of the overlays, laboratory pull-off tests (ASTM C1583) were conducted under cyclic freezing conditions to evaluate long-term bond strength, and salt ponding tests (AASHTO T 259) 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 overlays decreased sharply after 300 freeze-thaw cycles, whereas the bond performance of the LSDC overlay remained unchanged; the chloride resistance of the epoxy overlays is much better than that of the LSDC overlays; and the percentage of air voids in the substrate concrete was found to have an effect on the initial performance of the overlays.