Wind Farms Fill the Sails Of A Minnesota Concrete Pumper
A Minnesota concrete pumper is riding a wave of business with wind turbine construction that began with a relationship built nearly twenty years ago. Bob Swenson, owner of Bob’s Concrete Pumping, Parkers Prairie, and MN began pumping for Wanzek Construction, Fargo, ND when he was employed by a pumper in the early 1990s. Since starting his own pumping business two and a half years ago, Bob’s and Wanzek have collaborated on ethanol plant construction and most recently, wind turbine farms throughout the Midwest and as far south as Texas. The relationship must be working, as Wanzek has vaulted from No. 345 on Engineering News Record Magazine’s Top 400 US Contractors list in 2008 to No.145 in 2009. Their latest venture is a 105 turbine wind farm being constructed near Brookings, South Dakota. The key to their success? “It’s our working relationship. We have helped each other out and together we do a better job than anyone else,” according to Swenson.
Preparation by Wanzek for the Brookings project called Buffalo Ridge II has included construction of wind farms in Iowa, Texas and Nevada with pumping by Bob’s. The future for wind farms looks bright in South Dakota because the state ranks fourth nationally for potential wind capacity but is 18th in existing capacity, according to the American Wind Energy Association. Buffalo Ridge II will take the state’s wind-generated power capacity from the current 187 megawatts to 493 megawatts. One megawatt provides enough electricity for about 300 homes.
The area is ripe for wind farm development. Buffalo Ridge is a large expanse of rolling hills in the southeastern part of the larger Coteau des Prairies plateau which is approximately 200 miles in length and 100 miles in width rising from the prairie flatlands in eastern South Dakota, southwestern Minnesota, and Northwestern Iowa and is the second-highest point in Minnesota. It stands 1,995 feet (608 m) above sea level.
Because of its high altitude and high average wind speed, Buffalo Ridge has been transformed into a place for creating alternative energy. Currently, over 200 wind turbines stand in the area. Buffalo Ridge is also the first wind farm created in any of the states surrounding Minnesota. The project also includes a 13-mile, 115-kilovolt overhead transmission line that would connect to an existing collection substation near Brookings. Bob’s will be pumping a 500-yard slab for an intermediate substation used for power transmission and routing in addition to the tower bases.
Wanzek graded more than fifty miles of roads to reach the sites where towers will be erected. A wet autumn has required cement dusting of these rough graded roads to turn mud into a surface that can support pumping equipment. Eventually, Wanzek’s 650-ton crane will have to navigate to each pad site to erect the 150,000-pound towers and turbines.
Bases for the 250-foot tall towers are approximately 54-feet in diameter and excavated to a nine-foot depth. Bob’s utilizes a Schwing KVM 39X with horizontal reach of 114-feet to reach the pour area from one set-up. The 4-section Roll and Fold Boom unfolds quickly and the X-style outriggers provide fast set-up to move between multiple tower bases in a day.
The sequence of constructing the tower bases includes pumping of a circular footing followed by a 3.5-inch thick, 2,000 psi concrete mud slab to allow erection of 40-tons of reinforcing steel and the bolt cage. A 4.5-foot thick pedestal is poured around the rebar and the 120 bolts set in place to secure the tower. The resulting base consumes approximately 400-cubic yards of concrete. The mass concrete is 5,000 psi pumped at a 3-4-inch slump. Concrete is provided by an on-site portable plant. “The pump acts as a quality control device because the grading of the rock can vary,” explains Swenson, “If it doesn’t pump, often it’s because the gradation is off. Other placement methods such as conveyors throw whatever the plant provides, which does not protect the general contractor who is responsible for the structural integrity of the base.” Typically only 20-percent of the concrete is tested.
Swenson’s Schwing 39X is equipped with the 213 cubic yard per hour 2525-6 pump kit. “The plant only puts out 130 cubic yards per hour, “explains Bob, “So there is no problem keeping up.” The pump kit utilizes a slow-stroking design with 10-inch diameter, 98-inch stroke material cylinders. “It provides smooth output and reduces the number of strokes which reduces wear, “Swenson states. He also appreciates the low fuel consumption provided by the open loop design when far from diesel sources in the middle of the vast areas that accommodate wind farms. Wash out is expedited by the pump’s Rock Valve which cleans up faster and uses less water – another valuable commodity in rural areas.
Wanzek requires a back-up pump on-site which Bob has pressed into service. A Schwing KVM34X backs up the KVM39X with 98-feet of horizontal reach. It also serves as an excellent pump for placing the tower bases with a 2025-5 pump kit and 178 cubic yard per hour output. “We started the company with our 34 purchased new from Schwing,” explains Swenson, “We bought the 39 used from a ready-mix producer and then purchased two reconditioned Schwing 47s from Concrete Pump Repair (CPR).” Bob’s supplements the wind tower construction by using their longer booms for slip form silo construction and agricultural projects like hog confinement structures. “The 47s get us additional work we otherwise could not bid and with CPR we get a warranty on the used equipment which is our peace-of-mind,” Swenson added.
“On Buffalo Ridge II we are completing four bases a day with two pumps, so why leave one sitting? We send the operators out with the usual spare hoses, mud cups, fan belts and the small stuff that can kill you if you are not smart,” according to Swenson, “I appreciate the quality of the equipment. We have never missed a stroke.”
Many ACPA Members across the country are tackling wind farm projects. And Swenson has learned that equipment reliability and operator performance are two keys to success on these high yardage, remote projects. The future of wind farm construction is strong. While Texas, Oregon and Illinois are the top states in 2009 for new wind farms, the AWEA reports the fastest growth in the third quarter took place in Arizona, Pennsylvania, Illinois, Wyoming, and New Mexico.
Project: Buffalo Ridge II wind farm, Brookings, South Dakota
General Contractor: Wanzek Construction, Fargo, North Dakota
Pumping Contractor: Bob’s Concrete Pumping, Parkers Prairie, Minnesota
Equipment: Schwing KVM 39X truck-mounted concrete pump with placing boom, Schwing KVM 34X truck-mounted concrete pump with placing boom