Finite Element Analysis of Concrete Structures Subjected to Alkali-Aggregate Reaction

Abstract

The alkali-aggregate reaction was first reported in 1940 as a cause of severe cracking in some concrete structures. It is only in recent years that papers have been published dealing with the effects of AAR on the performance of structures. This thesis outlines a methodology for numerical simulation of the response of concrete subjected to continuing AAR. First a constitutive model is presented based on the framework proposed by Pietruszczak (1996). The formulation incorporates an assumption that the rate of expansion depends on the confining pressure, the age of concrete and the temperature. The progress in the reaction is coupled with the degradation of mechanical properties, in particular the elastic modulus and the compressive and tensile strengths. Subsequently, the procedures for generating finite element models are described, including geometric modeling, mesh generation techniques, graphical representation of the results and interfacing between pre- and post-processor and the finite element solvers. The numerical analysis, undertaken in this thesis, pertains to the Beauharnois Powerhouse, situated in Quebec, Canada. The powerhouse has been experiencing problems related to a continuing expansion of concrete due to AAR since the early 1960’s. The progressive formation of macrocracks and the volumetric expansion in concrete has caused operational problems, such as the reduction in clearance between turbine runner blades and throat rings. In this study, typical structural units of the Beauharnois Powerhouse were selected for the numerical analysis. The AAR constitutive model was applied in a finite element framework. Mechanical properties of concrete were carefully evaluated based on available experimental data. Simulations were focused on the deformation and the time history of progressive macro/microcracking due to continuing reaction. Structural responses under isothermal as well as non-isothermal conditions were simulated. The results of the numerical analyses were then compared with in-situ measurements.