Autogenous self-healing of cracked concrete exposed to the marine tidal zone

• The self-healing mechanism of concrete cracks exposed to the tidal zone is studied. • The crack width was monitored during marine exposure. • Hydration and carbonization are vital self-healing mechanisms for small cracks. • Brucite and calcite are the main self-healing products in cracks wider than 100 μm. The autogenous self-healing of cracks can reduce the risk of ingress of aggressive substances into concrete. Although autogenous self-healing mechanisms of concrete have been studied by simplified simulation experiments in the laboratory, few investigations have been carried out in the actual environment. This paper presents the autogenous self-healing mechanism of cracked concrete exposed to the marine tidal zone. The phases shown in the self-healing products were quantified by X-ray diffraction (XRD) and thermogravimetry-differential thermogravimetry (TG-DTG). The micromorphology of the self-healing products and elemental distribution in cracks were studied by SEM. The results show that the self-healing efficiency and composition of self-healing products are highly dependent on the crack width. For 50 and 100 μm cracks, the crack closure rate is 84% and 73%, respectively. Regarding 200 μm cracks, the average crack width is reduced, but partial self-healing of the crack is not observed. Cracks wider than 350 μm are increasingly enlarged due to spalling caused by the physical attack of ocean currents. Carbonization and rehydration are the main self-healing mechanisms of cracks more minor than 200 μm. Brucite is the main self-healing product in cracks larger than 350 μm. The micromorphology observation and quantitative analysis illustrate that seawater impurities are attached to the crack surface, which may hinder the crack self-healing.