The effect of restrained expansion on the assessment of structures with ASR

This report presents the results of a project in which the effects of restraint, both applied and induced by the stressing of reinforcement, on the expansion of concrete with Alkali Silica Reaction (ASR) were investigated. The effects of restraint on the properties of the concrete were also examined. It is shown that compressive stresses not only reduce expansion but also reduce the effects of the reaction on the concrete properties. However, tensile stresses have little effect on either expansion or concrete properties. Rate of expansion is found to have little effect on expansion. The use of crack widths to predict expansion is examined. It is shown that better results are obtained by consideration of crack angle in conjunction with crack widths than by considering crack widths alone. A formula is proposed that estimates the expansion of test specimens from crack width and crack angle data. The relevance of this formula to actual structures is discussed. Methods of modelling the expansion of restrained concrete affected by ASR are discussed. It is concluded that the use of such models is restricted by the amount of data they require. The application of the research to the assessment of structures affected by ASR is discussed. Reasons are given to explain why members with ASR, which are load tested, generally exhibit superior behaviour to that predicted from either the cores removed from them or parallel cast control specimens. (A)