Sunlight to heal mortar cracks: Photocatalytic self-healing mortar

Using capsules containing repairing materials to heal concrete cracks has always been a method of great interest to achieve self-healing concrete. Breaking the capsules to release repairing materials is a challenging task. The current methods used to break capsules mainly rely on instant external forces, which implies that slowly developing cracks cannot be healed by capsules. In this paper, we present a novel photocatalytic self-healing mortar to solve this problem. To do so, NaHCO 3 , Ca(OH) 2 and citric acid are inserted into macro capsules. Then, the photocatalyst TiO 2 is added to the insoluble shells of capsules to allow them to be broken by sunlight. After shells of capsules are degraded by sunlight, NaHCO 3 , Ca(OH) 2 and citric acid react in a wet environment to generate repairing materials that fill the cracks. To support the feasibility of the idea, physical and chemical experiments and characterization studies were conducted. Two-millimetre wide mortar cracks can be healed by the substances released from the photocatalytic capsules. The results of water permeability tests show that the two photocatalytic capsules can reach 52% healing efficiency. The characterization results show that the substances filling the cracks are unreacted NaHCO 3 , Ca(OH) 2 , citric acid and insoluble products of calcium salts. Our results suggest that sunlight can be used for the self-healing of mortar.