Poly(methyl methacrylate) capsules as an alternative to the ‘’proof-of-concept’’ glass capsules used in self-healing concrete

Development of suitable capsules is essential to achieve self-healing by encapsulation. In the context of self-healing concrete, capsules that can be easily mixed into concrete and release the healing agent when cracking occurs are ideally required. The optimization of these properties would allow for a successful implementation at large scale in practical (concrete) applications. In the present work, the suitability of polymeric cylindrical capsules made of poly(methyl methacrylate) (PMMA) to carry healing agent in self-healing concrete has been evaluated. An innovative method to assess more easily the capsules survival during concrete mixing was developed. This method is based on the evaluation of the setting behavior of concrete containing capsules filled with setting accelerator. Capsules with a wall thickness of 0.7 mm were able to resist the concrete mixing process and to rupture at relatively small crack widths (116 μm) after applying a surface treatment to increase the adhesion between the capsules and the cementitious matrix. Next, the self-healing efficiency of the encapsulation materials (glass or PMMA) was evaluated on real-scale concrete beams. The results showed that cracked concrete beams with mixed-in capsules (glass or PMMA) filled with water-repellent agent showed higher resistance against chloride ingress compared to plain cracked concrete beams. PMMA capsules showed a lower self-healing efficiency (in relation to chloride ingress) compared to glass due to a less favorable distribution of the capsules in the concrete. However, concrete containing glass capsules is susceptible towards alkali-silica reaction. Although optimization of the PMMA capsules is still necessary to improve their distribution in concrete and achieve higher self-healing efficiency, the obtained results indicate that these capsules could be a promising solution towards self-healing concrete.