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A new type capsule-based healing agent for concrete and its protective function of spores

To prolong the survival time of bacteria in the concrete and improve the self-healing ability of the late-age cracks, a new type of core–shell structure capsule-based healing agents were prepared for loading spores. The performance and protective ability of the capsules were tested. The self-healing concrete was prepared by mixing the substitution of fine aggregates with an equal amount of capsule-based healing agents. And the slump, compressive strength and repair-ability of concrete were carried out. The results showed that the capsule could provide long-term protection for loaded spores under the erosion of simulated pore solution of concrete for at least 203 d. Furthermore, the concentration and the cumulative amount of calcium ions of the crack zone solution were significantly increased. The slump and compressive strength of concrete do not change significantly with a low dose of capsule-based healing agents. However, the fluidity of fresh concrete will be greatly improved with the increase of dosage. Compared with adding spore powder directly, the self-healing ability of late-age crack (the repair-ability to crack area and the water impermeability of crack) will be improved obviously by adding capsules. Therefore, using capsule loading to protect spores is a potential solution for the long-term maintenance of the self-healing ability of concrete.