Mechanical properties, durability and self-healing performance of mortar containing double-layers capsules

To improve the self-healing performance of cementitious materials and minimize the negative impact of selfhealing materials on mortar, a novel type of double-layer capsules is developed in this study. The developed double-layer capsule includes the rapid hardening cement as the internal wall and polyvinyl alcohol (PVA) as the external wall. To evaluate its impact on mortar, two factors (i.e., capsule size and dosage) are considered and the correspondent experiments of investigating mechanical properties, durability, and self-healing performance are conducted. Experimental results present that the double-layer capsules reduce the flexural and compressive strength of mortar. With a reduced capsule size and a small ratio of the dosage, the negative impact the capsule gradually weakens. Moreover, the mixing of capsules slightly decreases the chloride penetration resistance and carbonation resistance of mortar specimens, while improves the frost resistance and impermeability greatly when the dosage is within 10%. Furthermore, the capsules can significantly improve the self-healing capacity of mortar. Especially when the capsule size is 2.36-3.2 mm and the dosage is 10%, the healing effect on matrix is highest. In addition, the XRD\SEM\XCT results indicated that the healing products mainly include C-S-H gel, CaCO3, Aft and Mg-containing compounds, the filling and bonding effects of which realize the automatic and effective recovery of matrix properties.