Canal contractor mobilizes for 30-month, 7 million-yd. schedule
One of the world’s largest concrete placements during the next two and a half years will add a third sets of locks to the Panama Canal. Scheduled for operation by the facility’s 100th anniversary in 2014, they will accommodate a new generation of East Coast-bound container ships to succeed the current 60,000- to 70,000-ton Panamax vessels.
In late 2010, the consortium building the locks began pilot concrete production through identical, twin-tower batch plants in Colon (Atlantic) and Panama City (Pacific), each equipped for nearly 800-yd./hour. After test mix runs, the plants are set to commence a March–April 2011 through late-2013 placement schedule requiring a combined 6 million to 7 million yd. of concrete.
With construction partners from Panama, Belgium, Italy and Spain, the Grupo Unidos por el Canal (GUPC) consortium enlisted SIMEM SpA to engineer and manufacture the mammoth batch plants. All equipment was designed and manufactured by Minerbe, Italy-based SIMEM and shipped to the sites. Each mixing tower is considered a separate plant, equipped with a computer-based control system, using soft PLC with distributed input/output architecture to simplify installation. All electrical panels have climate control to ensure a problem free operation.
San Antonio, Texas-based SIMEM America Corp. has overseen equipment installation and programming. Each plant consists of two towers bearing two, 6-yd. SIMEM MSO6000-HLS twin shaft mixers; operating on target 80-second cycles, they charge 12-yd., open-bed agitator trucks. A shared bin sized to supply material for one hour at peak output supplies each plant’s twin-mixer towers. The main concrete specification calls for five aggregates. Bins are split accordingly with a total of 10 dedicated scales—five weighing three coarse and two fine gradations for each tower.
KEEPING IT COOL
Beyond capacity, speed and meticulous controls for material handling and mix quality, SIMEM designed the plants to integrate with aggregate-cooling systems during transfer to the bin, plus ice charging for the main feed conveyor. The air-conditioned aggregate bins are fully enclosed with insulated panels. The cooling capacity is geared to a 50°F mix placement target on sites where temperatures average 95°F and above.
To ensure placing temperature is maintained, aggregate is loaded into the bins on a demand system. The control system of the concrete plant sends continuous consumption information to the aggregate loading system, which loads the bins with the different gradations as required. The aggregate is cooled during the loading process into the bins.
Cold air is also blown directly into the aggregate bins for some of the material fractions. Each mixing tower is served by a double set of ice scales, from which ice is discharged onto the inclined aggregate belt conveyor.
Twin silos feed each mixer individually weighed portland cement or supplementary binders. Primary cement supplier Cemex landed a 500,000-ton contract in mid-2010, announcing the agreement on the heels of a $300 million investment tripling Panamanian operations’ capacity.
One type of cement and one pozzolan will be used in most mix designs. The plant silos are charged from large cement storage silos by a pneumatic conveying system also supplied by SIMEM.
Cement feeding from the silos to the scales is done by the use of screw conveyors. There are two cement scales per mixer, one for cement and one for pozzolan to ensure the production capacity requirements are met.
Three types of admixtures are specified in the main mix design, and dosed with the use of two scale units—one double chamber, one single chamber. Due to the different volumes of the admixtures, two units were supplied to ensure the required accuracy.
Water is also dosed by the use of scale, and the plants are ready for use of clean water (chilled) and slurry water. The latter will be available from SIMEM Betonwash 25 concrete reclaimers. The MSO6000-HLS twin shaft mixers are equipped with a fully automatic, high-pressure cleaning system to ensure a quick and easy clean up. For consistency control, a mixer moisture probe combined with power consumption readings is utilized. The mixer moisture probe is not used in the traditional way of calculating the water requirement, but instead as an instrument to verify the moisture level in the mix towards a reference number.
Most of the concrete produced will be loaded into the open bed, 12-yd. agitator trucks, making it necessary to double batch to fill the truck. In order to reach the required capacity, each mixer was equipped with a holding hopper able to hold one batch, thus ensuring that the truck movement would not delay the mixer discharge. The plant is also equipped with an automated, moveable loading chute if traditional truck mixers are being used for deliveries.
The Colon and Panama City batch plants, coupled with a quarrying operation at the latter site, are part of a mobilization GUPC effected shortly after landing the contract in fall 2009. Three years prior, Panama voters approved a referendum to build the third set of locks, an infrastructure investment poised to keep the country competitive in an era of larger shipping vessels.
— Information and images provided by SIMEM America Corp., San Antonio, Texas, 210/581-8600; www.simem.com