Effectiveness of Silane in Mitigating Alkali-Silica Reaction in the Bibb Graves Bridge

Abstract

The Bibb Graves Bridge is in Wetumpka, Alabama, and it has severe damage caused by alkali-silica reaction (ASR) in two of its fourteen reinforced concrete arches. A silane-based, ASR mitigation procedure was developed and applied to the ASR-affected portions of the bridge by the Alabama Department of Transportation, the Federal Highway Administration, and Auburn University in 2010. The goal of this mitigation procedure was to lower the internal relative humidity of the ASR-affected concrete to below 80 percent so that continued ASR-related expansions cannot occur. After the application of the mitigation procedure, monitoring of the internal relative humidity, concrete expansion, and new crack development in the bridge was done for 34 months to evaluate the effectiveness of the mitigation procedure. The two ASR-affected arches and one non-affected arch received the mitigation procedure, and all three of these arches along with another non-affected arch were monitored. Analysis of the 34 months of data revealed that there were few signs of decreasing relative humidity or slowed expansion rates in the ASR-affected concrete. Thus the silane sealer was ineffective, and alternative mitigation options should be considered. Other options could include covering or confining the concrete.