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Abstract:The durability of the cooling towers of nuclear power plants (NPP) is an up-to-date issue: some of them can be affected by some cracks. Cracks formation is accompanied by some damages at the steel-concrete interface. These load-induced damages accelerate the diffusion of atmospheric carbon dioxide in the concrete and along the damaged steel-concrete interface. Carbonation at the interface induces steel corrosion which could cause the development of further cracks in the structure, thus, threaten its durability. To understand the effect of cracking, both in terms of corrosion initiation and propagation, an accurate experimental procedure leading to cracks and steel-interface damage representative of those existing on the cooling towers should be found. The objective of this paper is to characterize numerically and experimentally the damage induced at steel/concrete interface by the applied load during three point bending test. This would be determinant parameter for carbonation and then corrosion in RC structures as cooling towers of NPP.

This study examines the influence of the water to cement ratio (w/c) on the critical degree of saturation (DOSCR) of cement paste samples using length change measurements. Length change was measured using thermomechanical analysis (TMA) for cement paste samples with different degrees of saturation (DOS), ranging from 100% DOS to 0% DOS. The damage induced by a freezing and thawing cycle (FT cycle) was deduced from length change measurements. The results obtained from length change measurements were correlated with the amount of freezable water obtained from low-temperature differential scanning calorimeter (LT-DSC) tests. It was observed that samples with a DOS greater than DOSCR exhibited damage while those with a DOS less than DOSCR did not show damage. It was concluded that the DOSCR slightly increases when the w/c increases from 0.35 to 0.45. However, there was not a significant increase in DOSCR when the w/c increases from 0.45 to 0.55. However, it should be noted that freeze-thaw performance is dependent on w/c. Indeed, permeability of cementitious materials and the amount of freezable water are directly dependent on the w/c and directly affect the freeze-thaw performance of concrete.