Salt-Water Aging, Bonding, and In-Service Performance of a Novel Poured Silicone Expansion Joint Sealant for Small Movement Bridges

According to ASCE’s 2013 Infrastructure Report Card, over 200 million trips are taken daily over a structurally deficient bridge in the United States. One of the most commonly observed degradation factors that contribute to compromising the structural integrity of bridges includes leaking expansion joints which allow water, debris and deicing corrosive materials to penetrate through to the substructure. These corrosive agents can significantly damage the bearing and other key components of the bridge, hindering the lifespan of the structure. Currently, poured silicone sealant joint systems must be replaced every 2-3 years in Connecticut. A novel silicone foam sealant has been developed to provide a long term, cost effective sealing method for small movement expansion joints. The foam sealant, developed by chemically modifying the commercially available silicone sealant developed by Watson Bowman Acme Corp. (termed “solid sealant” herein), expands approximately 70% of its initial volume allowing for significant material savings compared to the existing product. Furthermore, the stress modulus of the foam sealant was observed to be significantly lower than that of the solid sealant, yielding reduced stresses at the interaction surface between the sealant and the substrate. This research work presents the laboratory experiments conducted to compare the bonding properties of the foam and solid sealant, as detachment from the substrate is a major concern. Each experiment contained some combination of variables such as varying substrate materials and primer application. A five-month aging study was performed to observe the adhesion characteristics of both sealants with and without the presence of road salt as a function of accelerated aging. The salt water aging experiment revealed that the application of primer onto the contact surface of the substrate yielded no significant difference in tensile and/or adhesion performance. The solid sealant’s ultimate strain did not improve and the failure mode was almost always characteristically adhesive. Similarly, the ultimate strain of the foam sealant did not significantly change when primer was applied, and the cohesive failure mode was also consistent regardless of primer treatment. Both sealants, however, exhibited a reduced ultimate stress and while the ultimate strain increased as a function of aging. Additionally, through the assistance of the Connecticut Department of Transportation, the foam sealant expansion joint system was installed on three bridges throughout the state to assess its performance under real conditions including environmental and vehicular effects. Both sealants were installed in a systematic manner to allow for direct comparison of their performance under the same conditions. Finally, field monitoring of the expansion joints was performed to understand the movement of each joint gap and determine whether the foam sealant can be considered as an effective sealing system under these demands while also monitoring the performance of the solid sealant. After several site visits, a few cohesive failures were observed in both sealants which were installed on the bridge with the largest joint gap. Two of these failures were located where the solid sealant was installed, while one failure occurred in the foam sealant. All three bridges are still undergoing consistent monitoring and visual inspection