The National Academies

NCHRP IDEA 20-30/IDEA 142 [Completed (IDEA)]

A Shape Memory Polymer Based Self-Healing Sealant for Expansion Joint
[ NCHRP 20-30 (NCHRP-IDEA) ]

  Project Data
Staff Responsibility: Dr. Inam Jawed

This project developed a shape memory polymer-based sealant for use in expansion joints in pavements and bridges to help prevent adhesive and cohesive failures through a self-healing mechanism, thereby minimizing the need for replacing the sealant. Needed raw materials, including shape memory polymer, microballoons, and carbon nanotubes were selected, the procedure for uniform mixing of the constituents established, the curing cycle and control parameters identified, and the physical and mechanical properties including the glass transition temperature and stress-strain behavior under uniaxial compression determined. Additionally, experiments on one-dimensional stress-controlled programming (with constant stress), free-shape recovery (with no stress), and isothermal stress-strain behavior were conducted. Subsequently, a two-dimensional programming device was designed and fabricated, and shape fixity and shape recovery ratios were determined. Laboratory-scale performance evaluation of the developed syntactic foam as a smart sealant for bridge and pavement joints was conducted that included uniaxial compression and tension and shear tests, water immersion tests, and functional stability under ultraviolent radiation. Two joints in a concrete pavement in the campus at Louisiana State University were identified. The laboratory testing showed that shape memory polymer, after 2-D programming, has a potential to solve two critical problems for compression-sealed sealant in expansion joints – accumulation of excessive compressive stress and squeezing-out-of the channel of sealant when the concrete wall expands in the summer. The laboratory testing also showed that the sealant had sufficient strength and stiffness under simulated traffic loading, thermal stress, and cyclic loading. The sealant was found to be functionally stable( i.e., maintaining its shape memory functionality subjected to various combinations of environmental attacks) and showed negative Poisson’s ratio at normal working temperature, which facilitates integrity of the sealant. The research also shows that the one-step 2-D programming can be replaced by a two-step 1-D programming and that thermosetting shape memory polymer can be cold-compression programmed. These findings lay a foundation for implementation of the smart sealant in practice. Shape memory polymer based sealant was fabricated, programmed, and installed in two joints on a bridge. Monitoring of the sealant’s performance will continue beyond the IDEA project by the Louisiana Department of Transportation and Development. Extensive field testing is needed before the technology can be implemented in the field in actual highway environment. The contractor's final report is available.

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