Meeting the quality level called for in the Panama Canal's new locks while producing the massive volume of concrete required to finish the job by the expected fall 2014 completion date has called for extreme equipment solutions. For each primary process—batching, conveying and placing—the material is tightly controlled.
The sheer volume of concrete—more than five million cubic meters—has to be built to meet the structures' projected century-long life span. As a result, the quality standards for the concrete are extremely high. The entire lock worksites on the Atlantic and Pacific sides—measuring about 1,400 meters long, 120 m wide and 45 m deep—boast a concrete batch plant engineered and manufactured by Italy's SIMEM. Each plant is designed to handle about 610 cu m per hour, with 10 dedicated scales to handle the five aggregate types required by the primary concrete specifications.
Both plants, each located next to a lock excavation, feature an industrial cooling system designed and built by Dutch refrigeration specialist N.R. Koeling. The cooling units include a wet-belt cooling system, an ice-making and delivery plant, a sand-cooling plant, a chilled-water plant and an air-blast cooling system.
With outside temperatures in Panama average 35° C or better for much of the year, it is critical to control the energy dissipation of the exothermic heat generated during the concrete curing process. To keep the concrete up to the project's stringent specifications (between 7.7° C and 12.7° C), each step of the mixing process features a special cooling measure.
Temperature control begins with the aggregate stockpiles, which are protected from the sun at each lock by a giant tent. At the start of the batching process, water cools the aggregate on its way to the bin, which is air-conditioned and fully enclosed with insulated panels.
Then, flake ice is introduced on the main feed conveyor. North Star Ice Equipment Corp., Seattle, provided a dozen of its largest flake-ice makers, four North Star modular ice rakes and eight day tanks, each with a capacity of 72 tonnes of ice. The forced-cooling systems at the canal project are capable of producing 670 tonnes of flake ice per day. While impressive, the volumes are actually less than other major projects on which North Star is currently working, says a company spokesman.
Once the concrete mix is produced, the next hurdle is transferring it to the site itself. The sheer size of the jobsite creates a logistical challenge that is complicated dramatically by the amount of concrete required for the locks themselves.
A fleet of open-bed, nine-cu-yd agitator trucks transports the mix from the concrete plants to the various locations within the job. Conveyors, used for large amounts of concrete at key locations, and pumping systems, which are set up at targeted locations on the floor of the locks, handle placement.