Reliability analysis of concrete deck overlays

Bridge decks are subjected to deterioration due to chloride ingress or other factors. Concrete overlays are used to replace the unsound concrete or to extend the life span of new concrete bridge decks. Overlay shrinkage is restrained by the substrate beneath leading to premature ingress of chlorides, corroding the steel reinforcement and producing delamination or spall of the concrete. This investigation quantifies the probability of the overlay cracking using mechanical strains as the main random variable. The analytical prediction of the time-dependent mechanical strains considers shrinkage strains from diffusion theory, tensile creep strains and the principle of superposition. Different overlay thicknesses, two types of substrates (concrete slabs and composite steel beams), and the impact of either not having or applying a water-proofing membrane are considered. Statistical parameters are computed from testing by others and testing conducted at Western University in Canada. Latin Hypercube sampling and Monte Carlo simulation is used to compute the probability of cracking. Analysis is performed for a fifty year lifetime of the overlay. Probability curves in time are presented and some recommendations about inspections are provided.