This paper presents the results of the numerical analysis of concrete dam structures which are affected by Alkali Silica Reaction (ASR) and subjected to seismic load. In this research a Chemo-Thermo-Mechanical ASR Finite Element numerical code is developed to model and analyse this phenomenon in concrete dams. It considers the effects of variables such as temperature, non-uniform time-dependent material degradation and 3D stress confinement on ASR evolution. The model is validated by modelling the mechanical response of the Fontana gravity dam and comparing the results with the actual data on macro crack appearance and crest displacement. While the structural behaviour of ASR affected structures under monotonic and quasi-static loading has been extensively investigated over the last decades, limited research has addressed the effect of dynamic loads on structures affected by ASR. The combined effect of old and new cracks under dynamic excitation may cause dam failure. The numerical simulations are used to assess and predict the dynamic stability of the Koyna dam considering fluid-structure interaction and are also used to investigate the evolution of damage associated with inception and development of macro cracks in the dam structure due to the combined effect of the synthetic ASR and realistic seismic loading on the dam. The results show that this combined action can significantly change the dynamic behaviour of typical concrete dams due to concrete material degradation and crack development.

Introduction

Dams are important infrastructure components and an asset for any country. Past earthquakes have highlighted their vulnerability to damage and even failure which can have major socio-economic consequences, losses and other cascading effects on e.g. water supply, power generation and irrigation. Hence, considerable efforts have been devoted to evaluate the safety of the aged dams and in some cases to pursue a suitable remedial action and rehabilitation strategy. Alkali Silica Reaction (ASR), a deleterious chemical reaction between siliceous aggregate and cement paste in concrete causes long term swelling and deterioration of concrete structures such as dams. The hydrophilic ASR gel expands in the presence of water, and initially fills the pores and micro cracks in the interfacial transition zone (ITZ) [1,2]. If reactive silica is not available at the aggregate surface, but contained within the aggregate particle, it takes time for the pore solution to diffuse into the aggregate and reach the reactive silica components. In such cases, the reaction proceeds more slowly and the gel forms within the aggregates. Thus, according to the mineralogy of aggregates, expansive gel may occur at the interior of the aggregate, or within the reaction rim at the cement paste-aggregate interface, leading to the distinction of late-expansive and early-expansive aggregates [3].