“The concrete was an especially tough mix with its 4-inch slump, and other brands of pumping equipment had difficulties placing it on various wind farm jobs throughout Texas,” says Ontiveros. The Putzmeister boom pump pumped the unforgiving mix without a problem, he adds.

“It's a learning curve and a timing issue with the specific concrete mix we engineered,” says Ortiz. “Everything has to be set up perfectly so we're ready to pump when the concrete arrives. If anything delays the process, the mix changes its slump, which then makes it tougher to pump. Since the specs don't allow us to add water, the pumping equipment is then forced to handle some rather difficult concrete.”

A Sweet market

Action pumped the structural concrete for each turbine's mud mat, foundation, and pedestal, relying on its Putzmeister BSF 32-meter truck-mounted boom pump. The octagonal foundation required concrete to be pumped at a shallow thickness along its sides, while increasing to a greater thickness at its center.

It resembled a shallow pyramid when viewed from its side. Centered atop the foundation was a wide pedestal, which required concrete to be placed within its tall, circular shape.

“It was critical that each foundation and pedestal support a giant 226-foot-tall turbine,” says Tony Baeza, Action's co-owner. “Everyone associated with the job was very particular about the concrete's strength and its precise placement.”

An incredible amount of reinforcing steel rebar was needed for each foundation and pedestal. “Although the center had a 9- to 12-inch rebar grid, the outer edges and pedestal had a lot less space between the steel bars, along with a bulkhead that we had to contend with,” says Ortiz. “These areas were more difficult to handle when placing and vibrating the concrete. Plus, any variation in concrete, such as larger aggregate size, would further complicate the project, making it difficult to even get a vibrator in these tight areas.”

The pumping company's 32-meter boom pump was needed for its 105-foot reach to easily access the pour within the rocky ground conditions. The machine was also specified for its rugged S-Valve, which could efficiently pump the unforgiving mix. However, the pump's high output capabilities were not put to use, as pumping was slow and methodical due to the precise concrete placement techniques required among the rebar.

As a result, each wind turbine foundation required three-and-a-half hours to pump, while it took a half-hour for each pedestal. Two foundations and two pedestals were completed per day.

Along with the jobsite challenges was delivery, as the secluded site made trucking the concrete a complex task. With a batch plant 35 miles away from the project's front gate and a jobsite covering another 37 miles, a ready-mix truck's journey to a pour could take up to one hour. A delay with any of the producer's 14 ready-mix trucks could disrupt the project.

Due to the critical mix design and the job's explicit requirements, Mortenson engineers assisted Sweetwater's batch plant personnel in updating to a computer system that would more precisely document its batch plant tickets.

“Sweetwater and Action did an outstanding job pumping the mix and meeting the project's demands,” adds Rick Ortiz. “As a result, we finished the project on time and within budget.”

For more on Putzmeister concrete pumps, visit the manufacturer's Web site atwww.putzmeister.com.Also, visit Putzmeister at World of Concrete booth #C5737.