Alkali-silica reaction (ASR) is a concrete degradation phenomenon in which the alkalis that are typically found in portland cement react with certain amorphous or micro-crystalline siliceous phases in the aggregate and, in the presence of moisture, form an expansive gel that is capable of cracking the concrete and generating macroscopic expansion. As the cracking occurs and progresses, there is a change in the mechanical properties of the concrete. Unfortunately, there is no standard guide or industry best practice for quantifying the reduction in the mechanical properties and the commensurate reduction in the structural capacity of ASR-affected elements. Furthermore, ASR is a complex chemical phenomenon, the rate and extent of which depend upon a number of material and environmental parameters, and the interactions among parameters is not fully understood. Therefore, although there are standardized test methods to characterize the susceptibility of a specific concrete mixture to future ASR degradation, there is no standardized procedure for assuring that a concrete mixture will be entirely immune to ASR throughout its intended service life. A scoping study of alkali-silica reaction in concrete is performed to support future activities that include evaluating the effects of ASR on the structural capacity. The study begins by summarizing the current knowledge of a number of technical topics related to the diagnosis, maintenance, and evaluation of concretes affected by ASR. The summary is then used to identify knowledge gaps for each technical topic. A technical plan is developed for filling in the knowledge gaps and for providing the tools that are needed to evaluate structural capacity of ASR-affected concrete and estimating the useful service life. iv v TABLE OF CONTENTS