We fabricated crack self-healing capsules using cement powder for mixing into cement composites and evaluated the properties of the capsule manufacturing process in this study. The manufacture of the self-healing capsules is divided into core production processing of granulating cement in powder form and a coating process for creating a wall on the surfaces of the granulated cement particles. The produced capsules contain unhardened cement and can be mixed directly with the cement composite materials because they are protected from moisture by the wall material. Therefore, the untreated cement is present in the form of a capsule within the cement composite, and hydration can be induced by moisture penetrating the crack surface in the event of cracking. In the process of granulating the cement, it is important to obtain a suitable consistency through the kneading agent and to maintain the moisture barrier performance of the wall material. We can utilize the results of this study as a basis for advanced self-healing capsule technology for cement composites.

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Self-healing cement composites are generally produced by using materials such as inorganic powders, bacteria pellets, and microcapsules. Among them, inorganic powder-type healing materials tend to decrease in healing performance over time because they react relatively quickly. Accordingly, this study encapsulated self-healing inorganic reactive powders in solid capsules (SC) in order to delay their reaction. The capsule surface was coated with a membrane to prevent moisture from permeating it. SC were utilized to provide the self-healing effect to the repair mortar. SC were mixed at three rates (0%, 5%, and 10%) by the binder mass of the repair mortar. The fundamental properties, including rheology, table flow, strength, and length change, and the self-healing performance of the self-healing repair mortar mixes were investigated. It was found that the rheological and mechanical properties of the repair mortar decreased slightly as the amount of SC increased. On the other hand, for a crack width of 0.25 mm and crack inducing age of 28 days, the healing performance of repair mortar specimens containing SC was at least 20 pt% better than that of plain repair mortar after a healing period of 28 days.

This study mainly aims to investigate the applicability of the combination of air-coupled surface-wave and computer-vision techniques to the evaluation of self-healing in in situ concrete members. Small-scale beam specimens were made from ordinary concrete and concretes with solid- and liquid-type capsules; the capsules were employed as self-healing agents. To monitor the crack healing progress, surface-wave tests using an air-coupled transducer and contact receivers were conducted on each specimen in uncracked, cracked, and healed conditions after 7, 14, 28, and 63 days of water immersion. Additionally, a computer-vision technique involving image binarization and registration was applied to measure high-resolution crack information. The specimens containing the micro-capsules showed superior healing performance compared to the ordinary concrete specimens. After 63 days of self-healing, the spectral energy transmission ratio increased up to about 80% of the uncracked, while the crack area decreased up to about 94% of the fully cracked. The healing rate was estimated using the change in spectral energy transmission ratio strongly correlated with that estimated using the change in crack area.

Abstract. In this study, we fabricated self-healing solid capsules using cement powder, an inorganic-based material that is the same as that of cement composites. Self-healing solid capsules can be divided into two stages(capsule core preparation and capsule wall coating). First, the capsule core mixes the core material and the coagulant to form a core material dough having a proper quality, and then puts into a capsule core manufacturing machine. the next, it was produced through the pore chamber under the pressure of the capsule core making machine. Second, The capsule wall is formed by placing the prepared capsule core into the chamber of the capsule wall coating apparatus and then applying the wall material while the chamber is rotating. The prepared capsules were mixed with cement composites to evaluate fluidity and strength. That is, we evaluated the basic performance changes of cement composite materials with capsules. We will use the results of this paper as the base data to consider the optimal amount of capsule at the level that satisfies the performance required when mixing capsules.