Thermomechanical Characterization of Shape Memory Polymer–Based Self-Healing Syntactic Foam Sealant for Expansion Joints

The failure of expansion joints is a leading cause for structural damage to bridge decks and concrete pavements. A fundamental requirement for sealant is that it should always apply a compressive stress to the concrete wall so that adhesive failure can be eliminated; also, the sealant must contract transversely (in the vertical direction) as temperature rises so that the sealant does not squeeze out of the channel. In addition, it is desired that the sealant has some self-healing capabilities so that cohesive failure can be healed. In this study, a shape memory polymer–based (SMP-based) self-healing syntactic foam sealant was prepared and tested. Special two-dimensional (2D) programming or training (compression in one direction and tension in the transverse direction) and free-shape recovery tests were conducted on the foam to evaluate its capability to serve as a sealant for expansion joints. The functional stability of the foam sealant was evaluated by repeated thermomechanical cycles. Furthermore, mechanical properties tests, including uniaxial compression, uniaxial tension, and interfacial shear, were also conducted. Results show that the smart foam sealant can eliminate the squeezing-out problem if programmed properly, and it has the potential to be used in expansion joints.