Thermo-chemo-mechanical modelling of hydropower structures affected by alkali silica reaction

Master Thesis


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University of Cape Town

Alkali-Silica Reaction (ASR) is a deleterious chemical reaction whose product expands in the presence of water inducing internal pressures within the concrete microstructure resulting in cracking and a reduction in elastic properties of concrete. Thus, ASR can substantially reduce serviceability and compromise the safety of concrete structures. To ensure the safe operation of these ageing structures, a sound understanding of the material deterioration and effect of ASR on the structural performance of these structures has to be developed. To this end, a number of numerical constitutive models have been developed to simulate ASR induced expansion in concrete. These models can generally be categorised as either, (i) microstructural models which aim to link the chemical process of the reaction to its impact at material level or (ii) macrostructural models which focus on the structural level assessment of affected concrete structures. Fundamental to most of these models is the assumption that ASR gets exhausted in time, which in the field, has thus far been rarely observed. In this study, a finite element model of a hydropower plant affected by ASR showing no signs of exhaustion even after 60 years of operation, was developed, validated and calibrated. From the analysis of the developed model in which a macrostructural thermo-chemo-mechanical ASR constitutive model was used to model concrete swelling, a prognostic evaluation approach to aid in determining the life expectancy of the hydropower plant was proposed.