Corrosion-induced cracking and spatial time-dependent reliability analysis of reinforced concrete structures

Research Doctorate - Doctor of Philosophy (PhD)Inadequate cover or poor quality concrete is the primary causes of reinforcement corrosion of reinforced concrete (RC) structures subjected to aggressive chloride environments (e.g. the application of de-icing salts or sea spray environments). Corrosion products (rust) are expensive, leading to the formation of tensile stresses in concrete and therefore subsequent longitudinal cracking and spalling of concrete cover. Structural collapse due to corrosion is rare. However, the observance of longitudinal cracking and spalling of concrete cover indicates the need for an assessment of existing safety, repair or rehabilitation, or the need for more frequent inspections. For these reasons, the serviceability limit state is considered for this study and a spatial time-dependent reliability analysis model is developed to predict the likelihood and extent of cracking and spalling. Probabilistic models for concrete properties, dimensions and corrosion processes have also been developed in this study. A time-dependent corrosion propagation model and a model to predict the time for cracking to reach a limit crack width (i.e., up to 1.0mm) has also been developed. This empirical model was based on results of accelerated corrosion tests of RC slabs conducted as part of this study. The corrosion rate and time to excessive cracking models are able to isolate the effects of concrete durability design specifications (e.g., concrete cover and water-cement ration) thus giving a more useful assessment of structural performance for different durability design specifications. A correction factor is quantified to correct any errors often associated with extrapolating accelerated corrosion tests results of cracking times to real RC structures. A spatial time-dependent reliability analysis model has been developed, which includes the spatial variability and uncertainties of variables related to concrete properties, dimensions and corrosion processes. Results of the spatial time-dependent reliability analysis are presented as: (i) the proportion of a RC surface subject to cracking and spalling and (ii) the probability of cracking and spalling, for various durability design specifications, limit crack widths, environmental conditions and for any size area. Spatial time-dependent reliability analyses were calculated for annual increments over the lifetime of a typical structure (120 years), in this case a RC bridge deck. The results show that the spatial time-dependent reliability analyses that only consider variables as homogeneous. Results of the analysis have also shown that durability design specifications, limit crack width and environmental conditions significantly affect the spatial time-dependent structural reliabilities