Development of performance control methods for concrete admixture of using the microcapsule

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Recently high-strength concrete and highly-flowable concrete have been developed. In such concrete, autogeneous shrinkage is not negligible and shrinkage-reduction agents are employed for preventing cracks due to the shrinkage. However, a certain amount of the agent needs to be used since a large part of effective components are absorbed by cement hydration products at an early age before the shrinkage starts. In this study, micro capsule technology was applied and surface coating techniques on the shrinkage-reduction agents were employed for controlling the chemical action process of the agents. In the surface coating layer, three different kinds of micro fibers crashed into pieces were mixed. One of the fiber was melt in alkaline water and the others were water-soluble. Experimental results showed that the chemical reaction rate of agents can be controlled by changing the coating thickness together with the type of micro fibers. It was also experimentally proved that autogeneous shrinkage strain in case of early-strength Portland cement was reduced by employing the proposed micro capsule.