Compression Set in Closed-Cell Foam Bridge Expansion Joints

Abstract

Closed-cell foam is used in small movement bridge expansion joints to create a watertight joint. It is popular for new joints and in the rehabilitation of joints because of its low cost, and ease and speed of installation. Some bridge owners, however, have steered away from using this seal because of failures after only a few years of service. The premature failure is potentially linked to compression set of the foam. Compression set is measured using a standard that requires the material to be held compressed for 22 h at 73°F, which is very different from what the foam will experience in-service. In this investigation tests were conducted to study the effect of compression duration, temperature, and recovery duration on the compression set of closed-cell foams. Tests were also conducted to study the effect of compression set on the tensile capacity of the sealed joint. Results show that compression set is dependent on all three of these factors. The values of compression set reported, when tested in accordance with the previously mentioned regulations, are not necessarily appropriate for bridge joint applications. Compression set should be measured by testing under conditions that are more reflective of the actual conditions the materials will experience in-service, when used in a bridge joint. In addition, the tensile capacity of foams that are appropriately bonded to the substrate are as good or better than that reported by manufacturers, even in the presence of compression set of the foam.