Why does the viaduct need to be replaced?

A:

The Sixth Street Viaduct was constructed in 1932 using then state-of-the-art concrete technology and an onsite mixing plant. However, just 20 years after the Sixth Street Viaduct was constructed the concrete began to disintegrate due to a chemical reaction known as Alkali Silica Reaction (ASR), causing significant deterioration of the structure.

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Over the years, various costly restorative methods have been tried, but none have worked to correct the problem. The results of seismic vulnerability studies, completed in 2004, concluded that the viaduct had a high vulnerability to failure in the event of a major earthquake. In addition, the Sixth Street Viaduct had geometric design and safety deficiencies. The Bureau of Engineering is leading the Sixth Street Viaduct Replacement Project, working in partnership with the Federal Highway Administration and the California Department of Transportation.

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