Water Permeability and Autogenous Healing of Cracks in Concrete

Abstract

The well-known practical phenomenon of autogenous healing in cracks plays a significant role in relation to the functional reliability of structures subjected to water-pressure loads. Because of the autogenous healing, the water flow through the cracks gradually reduces with time, and in extreme cases, the cracks seal completely. In the past, there has been no deliberate technical exploitation of self-healing, because too little is known about the phenomenon itself and about the chemical/physical processes involved. Based on theoretical and experimental research, the effect of crack healing was investigated on a larger scale for the first time. The experimental studies showed the formation of calcite in the crack to be almost the sole cause for the autogenous healing. A comprehensive theoretical discussion of the laws, which govern the calcite nucleation and the subsequent crystal growth of water-bearing cracks in concrete, revealed that the crystal growth responds to two different crystal growth processes that are determined by the changes in the chemical and physical conditions in the crack. Further, the crystal growth rate is dependent on the crack width and water pressure, whereas concrete composition and water hardness have no influence on autogenous healing. On the basis of the experimental studies, an algorithm that can be used to estimate the reduction in water over time as a result of autogenous healing was developed.