In the quest for an unlimited source of energy, man has turned to one of the earth's most plentiful resources—wind. The American Wind Energy Association envisions wind energy supplying 20% of America's electricity needs by 2030. That's a big leap forward, as wind presently accounts for less than 1% of the total U.S. electricity generation.
Although wind is only a small part of today's energy sources, it's big in Texas. Recently surpassing California, the Lone Star State took the lead in wind capacity production, at 2768 megawatts (MW) for 2006. This is ¼ of the total U.S. capacity, or enough to power more than 700,000 average American homes. Almost 1/3 of the U.S. wind generating facilities are being built in Texas, with 30% growth proposed for construction there.
“The growing number of wind farm construction projects means big business for Texas construction, and every contractor wants in on the action,” says Frank Ontiveros, general manager at Action Concrete Pumping in Grand Prairie, Texas.
Producers are also benefiting from this source of energy. For example, Sweetwater Ready Mix Concrete Co. recently supplied concrete for the foundations of about 200 wind turbines, and that seems to be just the beginning. “There are thousands out here,” says plant manager Greg Berwick.
Wind farms need wide open spaces to operate best. They are often placed in the middle of nowhere and this one was no exception. Berwick's experience with wind turbines occurred when his plant supplied concrete to Phase IV of the Sweetwater Wind Farm electric generation facility development for Sweetwater Wind Power LLC. The producer, about 50 miles west of Abilene, found itself involved a project that was challenging and rewarding.
The general contractor was Mortenson Construction's Energy Group of Minneapolis. The firm has built more than 45 of these wind farms across the U.S. Even more projects are underway, including 10 wind farms in nine states.
For the Sweetwater project, Mortenson's staff managed three phases of the six-phase development. Overall, their project scope included erecting wind turbines (previously known as windmills) along with building roads, foundations, collection systems, a transmission line, and a substation.
For Phase IV, Mortenson was responsible for the infrastructure to support 135 69-meter Mitsubishi turbines. Each turbine is capable of producing one megawatt of power that can provide electricity for 250 to 300 average homes in the U.S.
The producer supplied concrete for the infrastructure and the wind turbines. Depending of the size, they supplied 175 to 460 yards per foundation, totaling tens of thousands of yards of 4000 psi to 5000 psi ready-mix concrete.
“All wind turbine construction requires a similar concrete placing approach,” says Rick Ortiz, Mortenson's project manager. “However, the concrete specs differ on each project, being dictated by the size and type of wind turbine, along with the seasonal temperatures during concrete placement.”
As heat can quickly cure the concrete and clog pipelines in this hot southern state, the mix specified was a “hot” 5000-psi mix with plasticizers.
The pedestal required the mix to meet air entrainment requirements, which further made the concrete difficult to pump. Typically, crews had 45 minutes to work with the concrete once it was placed. But with the air entrainment spec, this turned into a limited 15 minutes before the concrete started curing.