Sechelt Supplies Bay Bridge: Quality Canadian Aggregates Requested for High Profile California Bridge Project

PHOTO CAPTION: The Sheila Ann, loading aggregates at the Sechelt Quarry outside Vancouver, British Columbia, for the trip down the coast to California.

It has been almost three years since Lehigh Pacific's Construction Aggregates Ltd.- Sechelt operation started supplying quality aggregates to this project's supplier in California. To date, the loading facility at Sechelt has loaded 61 ocean going ships, the largest of which carry approximately 70,000 M tonnes. They are called Panamax class ships because, at up to 115 feet wide, they are the largest ship capable of navigating through the Panama Canal. Suppliers have done an excellent job of marketing the aggregate coming from Sechelt. One example of this success is the Skyway section of the multi-billion dollar San Francisco - Oakland Bay Bridge project. The Skyway section is a precast segmental bridge almost 2 miles (3.2 km) long, which is part of the new East Span. The Skyway section will require the highest strength concrete ever used by CalTrans. Due to the massive foundations, the concrete has to perform to tight control restrictions related to heat released during the curing of the concrete.

PHOTO CAPTION: Segment E12E above is destined for the San Francisco-Oakland Bay Bridge. This segment is the largest precast roadway segment of its kind in the world, by an order of four times. It weighs more than 700 tons. Photo by KFM Engineer Govind Friedland. May, 2003.

Construction of the Skyway portion of the San Francisco - Oakland Bay Bridge project involves the placing of huge sections of precast concrete. This is done in varying winds and shifting tides, using some of the largest cranes available. Using highly skilled workers, the sections are maneuvered into place and joined by post-tensioned cables and high strength epoxy grout.

The precast sections are manufactured using the Sechelt aggregates and are then barged to the construction site. There will be 452 precast sections, some as large as 25 feet long (7.6 m), three stories high, 90 feet wide (27.4 m), and weigh as much as 780 tons (708 M tonnes).

The concrete specifications in this project called for compressive strengths of 8500 psi (58 MPa) at 56 days, but when other factors are taken into consideration (creep and elastic modulus) the concrete strengths are more in the order of 13,000 psi (89 MPa) at 28 days. A critical part of this performance is the aggregate.

"Aggregate imported from Canada was the only aggregate material that was able to satisfy the stringent concrete requirements, supplier technical services explained. "The aggregate also possessed very desirable thermal properties, which led to its selection for much of the foundation concrete."

The aggregates from Sechelt are mainly granitic in origin. They were deposited in a deltaic/ glacial environment during the last ice age. The aggregate has been stringently tested by independent testing facilities since mining operations began in 1989. These tests include petrographic analysis, durability performance, and alkali-aggregate reactivity in concrete. All tests have met the requirements as laid out by various standards associations, including Canadian Standards Association and the American Society for Testing and Materials (ASTM).

The Quality Control department at Sechelt continually monitors and adjusts the plant process to ensure that the aggregates maintain a high level of quality during production and shipping. This dedication continues to the most important part of the operation-the customer. Our supplier and Lehigh Cement Company have worked together to build a synergy of cooperation and trust that is illustrated by the success of aggregate shipments to California. Our customer's success is our success!

contributed by Jason Quinn, P. Geol., Quality Assurance Coord. / Geotechnical Services, Lehigh Northwest Materials Ltd.

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