Development, Field Testing, and Implementation of Improved Bridge Parapet Designs

Abstract

Premature cracking of concrete bridge parapets is a potentially complex problem, with several possible causes. The objectives of this study were to determine the reasons for uncontrolled concrete bridge parapet cracking and to provide recommendations to the Ohio Department of Transportation to prevent such cracking in the future. Potential factors examined in this study included properties of the concrete mixtures used, construction methods, joint details, composite structural action, and durability of the concrete and reinforcement. A total of 22 test bridge parapets were or will be constructed as part of this project to evaluate different approaches to address premature bridge parapet cracking. Both the use of polypropylene fibers and deep saw cuts through glass fiber–reinforced polymer (GFRP) reinforcement provided positive results for preventing early-age cracking. The use of fibers prevented the occurrence of any shrinkage or temperature cracking even though the control joints did not appear to function as designed in early observations. Performing a deeper saw cut of 3½ in. (89 mm) and cutting through the horizontal GFRP reinforcement allowed the control joints to crack easily, mitigating cracking elsewhere on the parapet. The most optimal design of a bridge parapet thus far seems to be including GFRP rebar as the horizontal reinforcement in the parapet to make a deeper saw cut for the control joints. At this point, none of the cracks between joints that were observed during the previous forensic study have been found on these new bridges.