Modelling the performance of ECC repair systems under differential volume changes

Most materials used in concrete repairs have a tendency to deform due to shrinkage, heat release at early age and ambient temperature change. The restraint of these deformations by substrate concrete induces stresses in repair systems. The stresses can lead to vertical cracking through the thickness of the repair material, peeling of the repair material from the substrate concrete and/ or delamination of the interface. ECC has been proposed to be one of the most promising repair materials. Unlike common cement-based materials ECC shows tensile strain-hardening behaviour with strain capacity in the range of 3-7%, which is hundreds of times of the strain capacity of common cement-based materials. Figure 1 shows the typical tensile stress-strain curve and the average crack width of ECC. The high ductility of ECC is achieved by multiple cracking. When ECC is used as repair material, the multiple cracking can release stresses in repair systems induced by differential volume changes. The risk of repair material in tension and interface delamination is therefore reduced. It can be expect that the use of ECC can enhance the durability of concrete repairs. This phenomenon has been demonstrated both in the laboratory and in the field. An analytical model was developed to calculate stresses in repair systems subjected todifferential volume changes. In this paper, this model will be further developed to estimate the performance of ECC repair systems under differential volume changes. The modelling results, with comparisons to experimental observations, are reported here.