A Shape Memory Polymer Based Self-Healing Syntactic Foam Sealant for Expansion Joint

Failure of expansion joints is a leading cause of damage to bridge superstructures. Cohesive and/or adhesive failure of joint sealant material facilitates decay of the structures beneath it. The objective of this study is to develop a novel smart joint sealant to self-heal cohesive damage and eliminate adhesive failure of expansion joints. This sealant will be a shape memory polymer (SMP) based syntactic foam material. A key feature of this sealant is that it utilizes the shape memory functionality for the purpose of self-healing damage. In particular, internal cracks can be narrowed or fully closed by confined shape recovery of the smart sealant. Also, the sealant can be programmed to consistently and autonomously apply a compressive stress to the edge of the concrete deck and restrict the upward expansion, so that adhesive failure or debonding can be eliminated and a smooth joint can be maintained. In this study, a shape memory polymer (SMP) based syntactic foam sealant was prepared by dispersing 40% by volume of glass microballoons into a SMP matrix. After curing, this foam sealant was first programmed under 2-D stress condition (compression in longitudinal direction and tension in transverse direction) by a specially designed 2-D test fixture and then freely recovered. The effect of the prestress levels and the number of programming-recovery cycles on the thermomechanical behavior and shape fixity and shape recovery ratios, was investigated. The potential of this sealant for eliminating adhesive failure and healing cohesive damage was discussed.