Prediction of structural effects in concrete affected by alkali-aggregate reaction
Alkali-aggregate reaction (AAR) is a chemical reaction between alkalis in concrete and certain alkali-reactive substances which are occasionally present in the aggregate. AAR produces a gel, which absorbs water, swells, inserts local stresses, and causes internal and external cracking in the concrete. Research on the reaction has been extensive. However, little research into the structural effects of AAR has been carried out and the effects are not yet adequately understood. The present research is to investigate the structural effects of AAR and to develop a numerical method for the analysis of the affected members. AAR affects the structural performance of reinforced concrete members in the following ways. • The expansion of AAR induces stresses in concrete and reinforcement and alters the bond stresses between the reinforcement and concrete. • AAR changes the material properties of the concrete. • AAR changes the bond properties between reinforcement and the concrete. To analyse an AAR affected member, the expansions within the member due to AAR have to be known. The main feature of AAR expansion is its stress dependency. This necessitates an expansion analysis to take into account the expansion and stress history of the concrete. A model for AAR expansion analysis is proposed, in which the basic variable is the free expansion and the restrained expansion of a concrete is governed by an instantaneous stress-expansion relationship. This model has been proved to yield good results. Experimental work to verify the assumptions made in the expansion model and also provide information on the deterioration of material properties of the affected concrete is described Material models are proposed based on the test results. The expansion model and the material models have been incorporated into a non-linear finite element computer program. Analytical results show good agreement with test data. The results of numerical studies carried out on singly reinforced beams conditioned with and without loading are given. The characteristics of structural performance of the beams found in the numerical studies are in general agreement with those found in laboratory and field testing. The numerical studies have helped to improve understanding of the effects of AAR on structural members. The method developed could be used to assist the future research and the appraisal of in-situ affected structures.