Self-healing of cracks in cement paste affected by additional Ca²⁺ ions in the healing agent

Cracks in reinforced concrete provide preferential access for aggressive substances into the concrete. Therefore, the corrosion of reinforcement bars is accelerated. Besides, carbonation, sulfate attack, and alkali–silicate reaction take place deep inside the concrete. Fortunately, from previous experiments, it was found that cracks in concrete can be healed with water and Ca is a main chemical element of the reaction products of self-healing. However, the ion concentrations in water can be various depending on the sources of water. There is still a lack of information on the effect of ion concentrations on self-healing. In this article, the effect of Ca 2+ ions on self-healing was investigated experimentally. Ca(OH) 2 was added into water as a healing agent. Self-healing behavior of cracks with saturated Ca(OH) 2 solution was explored and compared with that with distilled water. In order to gain deeper insight into the mechanism, the reaction products of self-healing were characterized by energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. In addition, the filling fraction of cracks as a function of time was determined by means of backscattered electron image analysis. The efficiency of self-healing induced by saturated Ca(OH) 2 solution was evaluated and compared with that with distilled water.