Accelerated Alkali-Silica Reaction and Corrosion of Reinforcing Steel in Concrete: Application on Dry Casks
The durability is one of the main reasons making concrete the most abundantly consumed material in the world after water. However, severe exposure conditions and improper or low quality mixture designs can cause physical and chemical changes in concrete which lead to deterioration and premature failure of the structure. This process is called aging. Two of the main aging mechanisms in reinforced concrete structures are corrosion and alkali-silica reaction (ASR). These two processes occur very slowly and to assess them in a short period of time, they need to be accelerated. Furthermore, these mechanisms are dependent on the geometry and boundary conditions of the structure. Therefore, research on these aging mechanisms is structure specific and depends on the scale of observation. This study proposes a method through addition of chemicals to the concrete mixture for accelerating aging that is applicable to both small- and large- specimens. The aging is accelerated through addition of sodium hydroxide to accelerate ASR and calcium chloride to the mixture to accelerate corrosion. The effect of the addition of these chemicals on both physical and mechanical properties of concrete was investigated through a series of destructive and non-destructive testing at the materials and structural levels. The results indicate that the addition of sodium hydroxide to the concrete mix, combined with the use of reactive aggregate and no fly ash, considerably accelerates ASR and crack propagation on the surface of the specimens. Similarly, the addition of calcium chloride effectively accelerates corrosion. To investigate the validity of the proposed approach at the structural level, a vertical concrete dry cask for storage of nuclear waste was chosen as the case study. In this case study, three 1/3-scale dry casks were subjected to accelerated ASR and corrosion with the addition of chemicals to the mixture and their effect was measured over eighteen months. Furthermore, the service life of the scaled down casks was estimated considering the real life conditions. This approach is expected to help researchers to better understand the long term behavior of reinforced concrete dry casks.