Effects of Bulk Water Chemistry on Autogenous Healing of Concrete

Autogenous healing can occur when hairline cracks in concrete repair themselves through reactions with water and/or constituents in water. The chemistry of water contacting the cement affects whether the crack heals autogenously or propagates until leaks occur. The strength testing on concrete specimens demonstrates that appreciable healing can occur at a pH of 9.5 when there is sufficient magnesium and silicon in the water. Scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) analyses indicate that a magnesium silicate material is present within the crack surfaces when higher strength healing has occurred. Calcium does not appear to promote the sealing of cracks. A carbonation of internal concrete surfaces was not detected when cracks were sealed via autogenous healing. Chloride diffusion rates do not return to levels seen in virgin concrete when cracks are autogenously healed. However, the water permeability and chloride diffusion are impeded by any filling of cracks regardless of the strength attained.