Effectiveness of Silane to Mitigate Alkali-Silica Reaction in a Historical Bridge

Abstract

Alkali-silica reaction (ASR) is a detrimental reaction in concrete that may lead to severe expansion and cracking in structures. The Bibb Graves Bridge is a reinforced concrete bridge that was constructed in 1931, and is located in Wetumpka, Alabama, U.S.A. Both arches of Span 5 have severe cracking and surface deposits caused by ASR. In order to mitigate ASR, a silane-based surface sealer was applied to Spans 4 and 5 of this bridge. The goal of this mitigation procedure was to decrease the internal relative humidity of the ASR-affected concrete to less than 80 percent so that continued ASR-related expansions do not occur. After the execution of the mitigation procedure, the internal relative humidity, concrete expansion, and new crack development in the bridge were monitored for 35 months to evaluate the effectiveness of the mitigation procedure. Analysis of these data revealed few signs of decreasing relative humidity or decreased expansion rates in the ASR-affected concrete. It is concluded that the silane sealer was ineffective and alternative mitigation options should be considered.