A parameter study on the age at cracking of bonded concrete overlays subjected to restrained shrinkage

Bonded concrete overlays form a common repair method for structures damaged by reinforcement corrosion. In terms of repair performance, overlay cracking is one of the most important aspects and needs to be minimized in practice. In this paper, the age of cracking of bonded concrete overlays with respect to various influencing parameters, including material properties, environmental conditions, curing duration, and overlay thickness, was investigated. Overlay stresses were calculated using a simplified analytical model that was previously shown to represent the cracking behavior of actual composite substrate-overlay specimens. Relevant overlay material parameters such as tensile strength, creep, shrinkage and elastic modulus were calculated according to the provisions given in BS EN 1992-1-1 (Eurocode 2: design of concrete structures; part 1-1: general rules and rules for buildings, 2004). Overlay cracking was found to reduce with increasing overlay strength, increasing overlay thickness, and increasing ambient relative humidity. A quantification of the influence of these parameters in isolation, as well as in combination with each other is presented and the relevance of various overlay material properties is discussed. The duration of curing was found not to have a significant influence on overlay cracking, longer curing resulting in poorer performance, especially in high strength overlays.