The interface enforcement healing mechanism of organic-inorganic interpenetrated network for microcracks in concrete

Reducing the microcracks in concrete materials is critical for extending service life and improving safety in civil engineering. Despite much progress in self-healing concrete materials, the meticulous research in healing mechanisms is still inadequate. In this paper, self-healing microcapsules are prepared by in-situ polymerization method and the interfacial enhancement healing mechanism of microcracks based on organic–inorganic interpenetrated network is proposed. The epoxy resin, as core material, was encapsulated by urea–formaldehyde resin to prepare self-healing microcapsules (PUF-E). The microcapsules were pre-embedded in concrete composites to achieve healing of microcracks. The concrete composites containing 5 wt% PUF-E microcapsules demonstrate significant self-healing efficiency, which can completely repair microcracks and improve mechanical strength. The compressive and flexural strengths of the healed concrete are 22.36 MPa and 3.73 MPa, with recovery rates of 98.90 % and 112.69 %, respectively. The self-healing mechanism with triple enhancement reactions is investigated. On the one hand, the rapidly releasing epoxy resin from PUF-E microcapsules fills microcracks and cures to form the first polymer network. Subsequently the second inorganic skeleton is introduced through the hydrogen bonding between epoxy and inherent hydration products (calcium silicate hydrate), building an interpenetrating structure with the polymer network. On the other hand, the coordination interaction between epoxy groups and Ca 2+ further improves the strength of the interpenetrating structure and enhances interfacial adhesion, achieving excellent self-healing performance of the concrete composites. The interface-enhanced healing mechanism of organic–inorganic interpenetrated networks provides new ideas for the design and development of high-performance self-healing concrete materials.