For over a year Shimmick Construction has been retrofitting the Dumbarton Bridge to make safety improvements and increase the its capacity to handle forces caused by earthquakes. The work included the reconstruction of bridge joints to allow for more movement of bridge segments without damage when an earthquake occurs. The joints are composed of heavily reinforced concrete covered by massive steel plates. The construction challenge for Shimmick and Graniterock, the concrete supplier of choice, was to get concrete to entirely fill the cavity under the steel plates through small holes drilled in the top of the steel plates. This meant the concrete needed to be highly fluid and flow freely to make its way around the dense steel reinforcing under the steel plates. The Caltrans specification also required that the mix not segregate into rocky pockets and sandy/cement pockets so that the strength and durability of the concrete was consistent throughout the joint.
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