Durability of epoxy polymer concrete overlays for bridge decks

Epoxy-based flexible polymer concrete overlays have been used in the past 15 years in North America to protect the bridge deck from deterioration, to extend the service life, and to improve skid resistant of the riding surface. While 15 years of field applications have demonstrated the effectiveness of the protection offered by the technique, cracking and delamination failures have also been observed.
The purpose of the research reported herein is to understand the mechanism of durability failure of the epoxy polymer concrete overlay system. The tests conducted were water permeability, chloride ion penetration, water absorption, strength loss, temperature cycling, and water vapour pressure. Methods of application of polymer concrete overlay play a key role in the success of the overlay. In addition to the two commonly used methods, the multiple layer and the slurry methods, five new application methods were proposed and evaluated.
It was found that the addition of a primer in the overlay system helps reduce water permeability, and that the thin polymer concrete overlay was much less permeable than the thick asphalt overlay. The temperature cycling tests revealed that no significant delamination occurred after 103 cycles from -50°C to 40°C at an accelerated rate. The rapid chloride ion penetration test confirmed that polymer concrete overlays did provide sufficient protection to stop the chloride ion intrusion. Nevertheless, the epoxy polymer concrete overlays were found to absorb 2--3% of water, which caused a significant strength loss. This strength loss could lead to cracking inside the overlay and accelerate delamination thereafter. The water vapour pressure generated from the saturated concrete substrates was not large enough to promote delamination. Overall, the newly proposed overlay applications methods have proven effective in constructing a thin, durable, less expensive and fast overlay for aged bridge deck protection.