Mitigation of alkali–silica reaction in US highway concrete

This paper provides an overview of the various field trials performed by the US Federal Highway Administration aimed at mitigating the effects of alkali–silica reaction on highway concrete elements, including pavements, bridges and barriers. The different methods used to attempt to reduce the expansion and cracking of affected concrete are described, including the use of sealings and coatings, the application of lithium nitrate and the application of external confinement. The field trials were conducted and monitored between 2005 and 2014, and the overall findings from each trial are briefly summarised. The use of silane products was found to be the most effective means of reducing the expansion and cracking due to alkali–silica reaction, with the most significant improvement seen in highway barriers. Topical and vacuum application of lithium compounds showed little or no benefit in reducing expansion and cracking, mainly due to the lack of lithium penetration. Electrochemical application of lithium nitrate was more effective in driving the lithium into the affected concrete, but had a negligible impact on the expansion and cracking induced by alkali–silica reaction. Owing to the limited time that was available to monitor most of the field trials, future monitoring is essential to delineate the efficacy of the various treatments.