Development of shape memory polyurethane based sealant for concrete pavement

Expansion joint failure is one of important causes to cause concrete pavement damages. To develop a new sealant to effectively seal expansion joint on concrete pavement, titanium dioxide/shape memory polyurethane (TiO2/SMPU) composites with a tailored transition temperature (Tt) was prepared, and effects of TiO2 content on various properties of TiO2/SMPU composites were discussed. The results indicate that TiO2 nanoparticles are uniformly physically filled in SMPU pores and wrapped by SMPU to form a compact skeleton structure when TiO2 content is suitable. The tailored shape memory Tt of TiO2/SMPU composites can be used as the shape memory switching temperature to match the working temperature of expansion joint in China. Also, TiO2/SMPU composites include amorphous phases or microcrystal structures which are dominated by the presence of crystalline rutile TiO2. The incorporation of TiO2 leads to the decrease in crystallinity of TiO2/SMPU composites. Additionally, a suitable content of TiO2 can obviously increase the absorptivity of SMPU to UV light in the wavelength range from 300 nm to 400 nm, and also improve the reflectivity to visible light, lowering photo-aging properties of SMPU. Further, TiO2 content shows a slight effect on shape fixity ratio of SMPU, but has an obvious influence on shape recovery ratio. Prepared TiO2/SMPU composites show satisfactory shape memory property after a two-stage biaxial programming process. Finally, mechanical properties of SMPU are improved by a suitable TiO2 content. The improvement in mechanical properties of TiO2/SMPU composites can better accommodate the working conditions of sealant. TiO2 content of 3% is proposed to prepare TiO2/SMPU composites with a specially tailored shape memory Tt, which can meet engineering requirements of expansion joints when used as a sealant of concrete pavement.