Why does the viaduct need to be replaced?


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.



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, in its current state of material deterioration and lack of structural strength, has a high vulnerability to failure in the event of a major earthquake. In addition, the Sixth Street Viaduct has geometric design and safety deficiencies and is in need of replacement. The Bureau of Engineering is working in partnership with FHWA and Caltrans to design and construct a new viaduct.