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Abstract
The alkali–silica reaction is a chemical phenomenon that, by inducing expansion and the formation of cracks in concrete, can have a severe impact on the safety and functioning of existing concrete dams. Starting from a phenomenological two-phase isotropic damage model describing the degradation of concrete, the effects of alkali-silica reaction in an existing concrete gravity dam are evaluated and compared with real monitoring data. Considering the real temperature and humidity variations, the influence of both temperature and humidity are considered through two uncoupled diffusion analyses: a heat diffusion analysis and a moisture diffusion analysis. The numerical analyses performed with the two-phase damage model allow for prediction of the structural behaviour, both in terms of reaction extent and increase of crest displacements. The crest displacements are compared with the real monitoring data, where reasonably good agreement is obtained.
Highlights
The alkali–silica reaction (ASR) is a chemical phenomenon that may occur over time in concrete between the alkaline cement paste and the reactive silica present in some kinds of aggregates
Structural Analysis of a Concrete Dam Affected by Alkali–Silica Reaction 4.1
The reaction extent evolution can be evaluated, through Equation (10). As this evolution depends on temperature and humidity, the development of the reaction is non-uniform inside the structure; in particular, the reaction is faster in warmer parts of the dam and expansion is higher in parts where the degree of saturation is higher
Summary
The alkali–silica reaction (ASR) is a chemical phenomenon that may occur over time in concrete between the alkaline cement paste and the reactive silica present in some kinds of aggregates This reaction causes expansion of the altered aggregate by the formation of a viscous gel, which increases in volume when absorbing water. While ASR can be avoided in new concrete structures by the selection of non-reactive aggregates and/or by the chemical composition of cement (which determines the alkali ion concentration in the pore solution [2]) and additions [3,4,5], ASR can lead to serious cracking in concrete structures built several decades ago in very wet environments (e.g., dams), resulting in critical structural problems. Several examples of important concrete structures, such as dams or shielding in nuclear plants, subject to ASR have been reported in the literature (see, e.g., [7,8,9])
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