Performance of Bond between Old and New Concrete Layers: The Effective Factors, Durability and Measurement Tests—A Review

With the rise in construction costs and aging of existing concrete structures, retrofitting and strengthening have gained more popularity. Among all of the available techniques, adding new repairing layers on top of old concrete ones has proven to be highly effective. However, the efficacy of such method is dependent on the performance of the cold bond between old and new layers of concrete whose establishment requires different considerations, such as paying attention to the properties of concrete layers, namely their strength, permeability, aggregate size, density, etc., and the qualities of the interface between the layer, such as how wet it is or its roughness degree. In this paper, the factors which can impact shear and tensile bond strength are fully discussed while being categorized into two major groups of factors related to each concrete layer’s properties and those directly associated with the connection area. The durability of the bond after exposure to various environments in terms of temperature and relative humidity is also addressed and then a list and comparison of numerous tests that are commonly conducted to measure the bond strength are provided. The findings indicate the characterization of suitable materials and surface roughening techniques which can ensure an adequate bonding between substrate and overlay, along with recommendations for the scope of future research.