When the evaporative cooling temps are not low enough, batch water is replaced with ice. A portable ice machine produced up to 100 tons of crushed ice per day. The ice system was mounted on two semi-trailers. The ice storage has a screw conveyor that feeds a scale system integrated with the batch console. The batchman enters ice as a mix ingredient (percent water). At the programmed sequence, ice is fed through the weigh system right into the mixer drum.
Liquid nitrogen is used when concrete temperatures must be below 55° F. A 5000-gallon insulated storage tank for liquid nitrogen was installed on each delivery barge. One minute of nitrogen discharge into a mixer drum containing 20 yards of concrete can drop the concrete temperature one degree. Mounted on the catwalk, the retractable nitrogen nozzles discharge directly into the barge mixer drums.Meeting budget
All of this was accomplished while staying within 1% of the plant and barge construction budget.
We are very proud that when the new San Francisco-Oakland Bay Bridge opens in 2013, Cemex's people, research, unique mix designs, and customized equipment have played a major role in not just making this 150-year bridge a reality, but also a stronger bridge that is built to be earthquake-resistant.
For more information on Cemex and details on the project visit www.cemexusa.com and www.baybridgeinfo.org.
— Alfred Kaufman is Cemex's project manager. Efirstname.lastname@example.org.James Van Nest is Cemex's project superintendent. Eemail@example.com.
Determining the proper mix designs for the San Francisco-Oakland Bay Bridge project had its own set of challenges.
Specialized testing of the structural concrete mixes for creep shrinkage and the thermal properties were necessary. In the mix development process, we found the governing properties would be thermal and Elastic Modulus (MOE). Special “Q-drums” determined the thermal “heat signatures” for each mix that the contractor used to develop thermal control criteria for each concrete placement. Most of the creep measuring equipment in the United States is required to satisfy the specification requirement for one-year creep values.
Although not part of the initial project scope, two specialized concrete mixes were the most challenging. Both lightweight, self-consolidating concrete and non-shrink, neat cement annular grout with steel fibers needed special handling equipment.
About 3500 cubic yards of 11,500-psi annular grout sealed the steel pilings and street foundation boxes. To ensure grout quality control, we used test equipment normally used in oil fields to test well grouts. Density testing was required for each batch of 11,000-psi grout produced for the project.