Study of Concrete Surface Coatings Using Thermosensitive Fluorescent Microcapsules Capable of Indicating Damage

A new type of concrete surface gel coating using thermosensitive fluorescent (TSF) microcapsules was proposed to monitor micro-cracks of cement-based materials. The gel materials can adhere other materials, and the incorporation of microcapsules into the gel coating can be cured on various structural surfaces. Zinc sulfide and phenyl acetate were encapsulated into a polymethyl methacrylate shell to prepare the TSF microcapsules by a solvent evaporation method. When micro-cracks are generated on the surface of the gel coating, the ruptured TSF microcapsules burst out, fill the damaged area, and then emit fluorescence after being excited at ambient temperature. It was found that the brightness of the fluorescence increased with increasing temperature from 80–110 °C. When the concentration of TSF microcapsules was 15% of the mass of the gel coating, the cement-based damage-sensing material had sufficient damage-indicating effects, and the fluorescence brightness of the crack location remained even after a long time. It is expected that this study will provide an effective and intuitive method for crack location detection of cement-based materials.