Pumpable fill speeds construction of a solar panel plant.

A second solar panel fabrication facility nearing completion in Fremont, Calif., symbolizes the trend toward clean energy technology serving both environmental responsibility and economic recovery. The new plant, called Fab 2, will add more than 600,000 square feet of production and office area, allowing Solyndra Inc. to meet the rising demand for its products while creating more than 1000 new jobs. Efficient management of the extensive concrete foundation and slab placement has helped to keep the project on track.

Site conditions influenced both the design and execution of the concrete work. Because the plant is located in a seismic area on top of underground warm springs, San Francisco-based Degenkolb Engineers designed a concrete mat and keyway foundation system tied deeply into the ground. Custom forms were used to provide keyways up to 10 feet deep that serve to interlock the 12 mat slabs. The mat and keyway system takes the place of drilling and filling hundreds of piers for the foundation. Additionally, the urban site is hemmed in by freeways and other industrial development, therefore concrete contractor Joseph J. Albanese Inc., Santa Clara, Calif., placed much of the concrete at night, when ready-mix trucks could gain access more easily.

Albanese used its fleet of 16 Schwing boom pumps to place all of the concrete for the Solyndra plant. The work began with the pumping of 4-inch-thick "rat" slabs, on which the reinforcement was set for the mat slabs. The 12 mat slabs were poured one at a time, using four to six pumps to place up to 7000 yards per 12-hour shift. The mat slab concrete features a 4000-psi mixture with a 6-inch slump. Mike Aldrich, Albanese pump division manager, says his crews were working 24/7 when they began the project in September 2009. "The steel guys would set rebar during the day, and then we'd pump from 4 p.m. until 4 a.m. the next morning," he says.

Larger pours were done at night to facilitate access for ready-mix trucks.

CDF saves time and money

Once the foundation slabs were in place, the excavation had to be filled to elevate the grade for construction of the topping slabs. In some areas, the top of the mat slab was as much as 6 feet belowgrade. The initial plan was to backfill with earth topped with a course of pea gravel, but Albanese chose instead to use a cementitious controlled-density fill (CDF). A lean concrete mix with only fine aggregate, CDF offered several advantages. It is a pumpable, flowable liquid that is self-leveling without compaction and hardens within hours, typically reaching a compressive strength of about 300 psi.

Long booms were used to place concrete for foundation mat slabs and topping slabs. PHOTOS: JEFF BAYER

Albanese crews built walls belowgrade to serve as permanent forms for the CDF. Then they used 47-, 58-, and 61-meter boom pumps to place the fill material in 2-foot lifts and raise the grade. From November 2009 through February 2010, the contractor placed about 65,000 cubic yards of CDF, averaging 1000 yards per day per pump. The entire process took considerably less time and effort than earth backfill, and provides better support for the topping slabs as well. Aldrich says, "We've used CDF a lot to cover pipelines, so we're very familiar with it. It pours almost like water, so it's fast and easy to place."

Topping slabs

The 12-inch-thick topping slabs were formed and pumped in 10x190-foot sections, then machine-finished to meet an FF40 flatness specification. Work proceeded at a fast pace, so some of the steel framing for the second floor and roof deck already had been erected while later sections of the topping slabs were being placed. Experienced pumping crews working with articulating-boom pumps were able to maneuver the pump hoses wherever they needed to go on the congested site.

Federal financing intensifies safety

Solyndra designs and manufactures photovoltaic systems that use proprietary cylindrical modules and thin-film technology to produce high solar energy output at a low installed cost. The equipment produced at the new Fab 2 facility is expected to generate 500 megawatts per year, enough electricity to supply 150,000 homes. Solyndra reports that its two manufacturing facilities will produce enough solar panels over their lifetimes to cut 350 million tons of CO2 or 850 million barrels of oil. To help fund the Fab 2 project and support clean energy technology, the company received a $535 million loan from the U.S. Treasury, guaranteed by the Department of Energy under Title XVII of the Energy Policy Act of 2005.

This federal financing has resulted in additional inspections during construction and a more intense emphasis on safety. Aldrich believes that Albanese Inc.'s concern for safety and its commitment to American Concrete Pumping Association, Lewis Center, Ohio, certification for pump operators has helped the company compete successfully for major projects. ACPA has recently introduced a series of improvements to its certification program

Kenneth A. Hooker is a freelance writer based in Oak Park, Ill.