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RCC Hydro

Limestone

Currently, two major milestone U.S. roller compacted concrete (RCC) flood control dam construction projects are nearing completion. In the first of a two-part report, we focus on the Portugués Dam being constructed by the U.S. Army Corps of Engineers (Antilles) District in Jacksonville, Fla.

Next month's Concrete Products will describe a RCC hydro project by the San Diego County Water Authority, with work nearing completion in Lakeside, Calif., on the San Vicente Dam Raise. These projects mark the largest RCC hydro projects undertaken in the United States since the Taum Sauk Reservoir in southeastern Missouri was completed in 2009.

In the East
The Portugués Dam is located northwest of the city of Ponce, Puerto Rico, and is the first arch dam in the in the United States constructed with RCC. The U.S. Army Corps of Engineers and the U.S. Bureau of Reclamation, together with the project sponsor, the Puerto Rico Department of Natural and Environmental Resources, are constructing the project. When completed, this flood control dam will stand 220-ft. high, with a 11-ft. base and a 35-ft.-wide crest spanning 1,230 ft. It will contain an estimated 367,000 cu. yd. of RCC laid in 24-in. lifts delivered by overland belt conveyor and dump trucks, spread, leveled and compacted with road-building equipment.

The U.S. Army Corps of Engineers, Jacksonville District, awarded the contract for construction of the Portugués Dam at a base value of $180 million to Dragados USA, Inc., of New York City. Dragados had completed other monumental projects in Puerto Rico in the past, and is the world’s leading RCC dam builder, second only to the Chinese government in projects completed to date.

At 4,000-ft. elevation in a rainforest, the Portugués River is barely a creek most of the year at a mere 11 cubic feet per second. However as the rainy season sets in, the soil conditions and the steep terrain combine into a deadly force of floodwaters rushing toward the seaside city of Ponce at hundreds of thousands cu. ft. per second. The spillway now nearing completion by comparison, will allow 47,000 cu. ft. of water to breach the dam crest by design. The freshwater storage will equal 215-plus-acre flood pool and provide a multipurpose reservoir while saving much reoccurring human suffering and financial loss.

The project is located approximately three miles northwest of the city of Ponce on the Portugués River. Appurtenant structures include an integral spillway and intake. A valve house and control room for reservoir operation is located just downstream adjacent to the river. Work also includes foundation excavation in rock, placing foundation concrete, foundation grouting and development of an on-site quarry for concrete aggregate production.

The Portugués Dam project is cost-shared with the Puerto Rican government, with the U.S. federal government providing 75 percent and the local sponsor, the Puerto Rico Department of Natural and Environmental Resources, providing 25 percent of the required funds. Construction started in April 2009 and is scheduled for completion this summer.

Challenges & methodology
The project contract required that only a six month per year construction window be allowed due to ferocious river conditions and massive flooding of the area during the monsoon season, which normally starts in midsummer—coinciding with hurricane season. To make matters even more challenging, the area is prone to earthquakes and required seismic design of the RCC dam and appurtenant structures, as well as the project’s stationary equipment.

The contractor chose to utilize its proven worldwide formula with regard to both the production of the RCC and the required cooling of the RCC. Dragados-USA teamed up with San Antonio-based Plant Architects + Plant Outfitters in designing and building the entire production and cooling system. Large bolt-together silos were utilized to store several days of aggregate production.

Plant Architects designed an overhead conveyor system to fill the three large-diameter tanks set atop a cast-in-place concrete reclaim tunnel, which feeds dual wash screens and two 300-ft.-long chilled water (recirculation) wet belts for chilling the individual coarse aggregate. The coarse aggregate is chilled one type per belt at a time and then dewatered on the shale-shaker-type polyurethane decks at the discharge end of the wet belts prior to feeding a customized overhead conveyor system to twin five-compartment aggregate batching plants equipped with individual weigh batchers.

The fine aggregate is cooled by air and fed by a customized overhead conveyor system to two large-diameter, bolt-together storage tanks. The sand is then reclaimed from the tanks by an automated programmable logic controller (PLC) and sent to the twin batching plant overhead bins on a automated demand basis.

Cement and pozzolan are stored in two large-diameter, bolt-together silos, each holding 1,000 tons of bulk powder, allowing for ensured storage inventory to the remote rainforest location, and providing much needed temperature stabilization. The bulk powders are transferred pneumatically from the two bolt-together storage tanks to the dual overhead silos on each of the redundant batching plants.

Large-scale ice plant
In mass concrete placement schemes of structural slump-type concrete and in RCC for mass structures, cooling of the constituent solids material is normally undertaken. The aforementioned dual wet belts are used for the chilling of coarse aggregate, air cooler for the fine aggregate and large-capacity storage of each of these and the bulk powders. Added to this is the chilling (or sometimes super-chilling to 32.5° F) of the batch water. These forced cooling measures are utilized in addition to certain passive cooling measures (the large containment of the constituent materials) such as shading, solar reflective material finishes and enclosures of both materials and the production equipment.

In addition to these measures, where excessive wet bulb temperatures are encountered (combined heat and relative humidity), it is also necessary to further cool the resulting concrete produced. Dry flake ice was the choice of Dragados-USA and Plant Architect’s specialty construction division, Concrete Temperature Control (CTC). Dry flake ice was chosen over liquefied nitrogen due to the remote location of the site and the owner’s specification that several days' production materials be kept in inventory onsite. CTC designed and built a large-scale dry flake ice factory producing 150 tons per hour and storing 400 tons of ready-made dry flake ice in a refrigerated enclosure with automated reclaim by live-bottomed floor devices to a pneumatic transfer to insulated ice storage tanks fixed on each of the dual batching plants.

Dual Plants, Twin-Shaft Mixers
For the multipurpose mixing of grouts, slurries, structural concrete, and of course the large quantities of RCC, Dragados chose to equip the two batching plants with two 6-cu.-yd. output, twin-shaft, high-intensity, low-shear batch style mixers from OMG-Sicoma. The mixers received a factory refit with Plant Architects-designed PneuSeal air-type shaft seals patented by Inpro-Seal to avoid undue shaft seal issues.

Each mixer provides 150 cu. yd. of concrete per hour, and operates independently of the other. The mixer structures are a Plant Architects collapsible tubular design, which use no bolts, but rather pins and turnbuckles for fast assembly, all erected on skid bases.

Further information on this project can be found at the U.S. Army Corps of Engineers, Jacksonville District website: www.saj.usace.army.mil, and click on the “Portugués Dam, Puerto Rico” link. More information on the design-build offerings of Plant Architects + Plant Outfitters, or CTC concrete cooling and dry flake ice plants visit can be found at www.robertober.com. Information on Dragados-USA is available at www.grupoacs.com