Effect of cycling temperature on propagation of tensile fatigue cracks in concrete mass dams

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A stability review of monolithic concrete dams in Manitoba discovered that if a crack was initiated by cyclic thermal stress, the subsequent increase in internal water pressure via the crack would cause the crack to propagate leading to increased risk of instability of the structure. Manitoba Hydro initiated a project to review, research and test to ensure the tensile strength of the concrete, particularly at construction joints, can continue to be relied on to provide the cohesion necessary for safety against sliding failure. Research and testing of concrete is required to evaluate strength deterioration due to thermal cycling. The finite element analysis (FEA) performed as part of the stability review shows that the seasonal warming and cooling of the mass concrete structure generates an annual cycle of differential movement causing the stress in the upstream face of the dam to shift between tension and compression. The risk to the dam stability from crack propagation initiated by these temperature cycles and subsequent tensile fatigue in mass concrete are not well understood. This project will help to estimate the rate of crack growth under thermal cycling. The objective of this study is to investigate the impact of the temperature fluctuations and resulting cyclic tensile and compressive stresses on the long-term durability of concrete, and the impact on the durability of the construction joints. This study will train nine HQP, three each at the Master's and Bachelor's level, one Ph.D. student and two post-doctoral fellows. This research will enable Manitoba Hydro and other dam owners to assess the safety of these structures against possible instability due to cracking. The results will inform the ongoing Manitoba Hydro dam safety program through better understanding of threats to stability as well as modifications to monitoring and surveillance, if required.