Abstract
A number of hydraulic structures such as dams and hydro-power plants in the world and in particular, in South Africa which have been designed and built during the last decades, have been subjected to material deterioration due to Alkali Silica Reaction (ASR). ASR is a deleterious chemical reaction between the alkalis in Portland cement paste and certain amorphous silica found in various types of natural aggregates which usually results in material degradation and structural distress such as expansion of the structure, cracking, presence of gel, discoloration and pop outs of the reacting particles near the surface of the concrete. Also, suitable environmental conditions (temperature and relative humidity) play a vital role in the initiation and advancement of ASR. In this study a chemo-thermo-mechanical model is developed to predict the structural expansion, degradation of mechanical properties, cracks and damage in concrete structures affected by ASR. Parameters such as temperature, kinetics of the reaction, confining stresses and material degradation are included in the model. The finite element based model can simulate the temperature field in the structure and the kinetics of the chemical reaction to predict the long-term effects of the ASR on concrete structures including displacement, cracking and damage development. The model is applied to an actual concrete dam subjected to ASR. The results are interpreted, and support the management and evaluation of the remedial measures for repair and maintenance programmes for the affected dams.
Highlights
Alkali-Silica reaction is a deleterious chemical reaction between alkalis in Portland cement paste and certain amorphous silica in a variety of natural aggregates
In continuum mechanics one can read the total strain as a superposition of strains from different mechanisms involved in the medium such as: ε = εel + εpl + εth + εasr
The results indicate that the Alkali Silica Reaction (ASR) expansion is volumetric in free stress state tests and transfers to the less compressed direction
Summary
Alkali-Silica reaction is a deleterious chemical reaction between alkalis in Portland cement paste and certain amorphous silica in a variety of natural aggregates. Mathematical models for modelling ASR and its effects fall into three main categories: (1) macrostructural models concerned with the analysis of structures affected by the reaction [Charlwood et al [7], Ulm et al [8], Capra and Sellier [9], Saouma and Perotti [10]]; (2) microstructural models which aim to link the chemical process of the reaction to its impact at the material level [11,12]; (3) mesoscopic models [13,14] These mesoscopic models take into account the multiphase nature of the aggregate, cement paste, void and ASR gel, anisotropy can be explicitly represented in the concrete material model. The results are interpreted, and support the management and evaluation of the remedial measures for repair and maintenance programmes for the affected dams
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