Silica-based self-healing microcapsules for self-repair in concrete

New self-healing material for concrete repair has been fabricated through microencapsulation of silica sol via interfacial polymerization of poly(urea-urethane). Smooth, uniform, and spherical capsules of 60-120 μm sizes were synthesized and optimized by studying the emulsification and polymerization steps of its synthesis. A hydrophile-lyophile balance (HLB) value of 3.0-5.0 and a rotational speed of 500 rpm were necessary to produce a stable emulsion system of silica sol in surfactants. The polymerization speed of 900 rpm and the methylene diisocyanate (MDI) monomer content of 15 wt % were both significant in getting the right size and smoothness of the microcapsules. With this method and cheap healing agents, industrial scale-up is highly possible. The viscoelastic properties of the microcapsules were examined, and further characterizations were carried out through scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. After healing the microcracks in concrete, the results showed that the significant increase of compressive and bending strengths manifested the self-healing ability of the microcapsules in concrete. © 2015 Wiley Periodicals, Inc.