This report is based on a critical review of the literature on the structural implications of the alkali silica reaction (ASR) in concrete. The implications of the review for structural assessment, and in particular, the assessment of highways structures, are considered in terms of possible critical elements and the use of British Standard BS5400: Part 4: 1984 (see IRRD 282725). The available methods for assessing the strength of structural elements are briefly considered and recommendations made to allow for the effects of the reaction in the various methods of assessment. The report concludes that relatively small amounts of reinforcement or applied compressive stress can significantly reduce expansion due to ASR compared with free expansion. However, it is not possible at present to predict restrained expansion from a knowledge of free expansion. ASR modifies the mechanical properties of concrete: both strength and stiffnesses are reduced. In the range of expansions which generally occur in practice, reductions in compressive strength, tensile strength and elastic modulus of up to 25%, 50% and 60% respectively, could occur. These values refer to isolated unreinforced and unrestrained cylinders of prisms and may not be applicable to concrete in a structure where it is restrained by adjacent material. Tests on under-reinforced concrete beams and post-tensioned concrete beams show no significant change in service load behaviour or reduction in strength as a result of severe ASR cracking. Shear cracking is less likely to occur in a beam affected by ASR even if there is no shear reinforcement or the main reinforcement is poorly anchored. Pull-out tests have shown large reductions of bond strength of bars with small covers not restrained by links, but only small reductions for bars which are restrained. Loading tests on structures badly affected by ASR have predicted no significant adverse effects of ASR on either strength or stiffness. The report also discusses the situations most likely to be seriously affected by ASR and those topics requiring further research. (A)

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