Benicia-Martinez Bridge

The Benicia–Martinez Bridge carries northbound Interstate 680 traffic across the Carquinez Strait in the San Francisco Bay Area. Designed as a major seismic-resistant lifeline structure, the bridge was built to remain operational following a major earthquake due to its proximity to the Green Valley Fault.

The structure consists of a cast-in-place, balanced cantilever segmental concrete box girder with spans reaching approximately 659 feet. Lightweight concrete made with Stalite Lightweight Aggregate was used throughout the box girder superstructure to reduce overall structural mass while maintaining high strength and durability. Lower structural weight reduces seismic forces transmitted through the bridge during earthquake events, improving overall structural resilience.

The 1.5-mile bridge includes 22 spans supported by 16 piers, with most spans located over water. Cast-in-place lightweight concrete segments were constructed using form travelers, with segments extending from both sides of each pier. The use of structural lightweight concrete enabled longer span lengths and improved structural performance without increasing foundation demands.

To achieve the required material properties, the concrete mix used normal-weight sand combined with Stalite Lightweight Aggregate to produce structural lightweight concrete with a density of approximately 120–125 pcf. Extensive testing and mix development ensured the concrete met strength, modulus, and pumping requirements for the balanced cantilever construction process.

Construction required innovative placement techniques, including barge-supported pumping systems capable of delivering concrete more than 180 feet above the water. The lightweight concrete allowed the bridge to achieve long spans while reducing loads on foundations and improving seismic performance in one of the most demanding seismic regions in the United States.