The ground near Colstrip, Montana, often shakes without causing alarm to the local residents. The ground movement is the result of dynamite blasts at Western Energy Company’s Rosebud Mine, a 25,000 acre (10,117 ha) surface mine complex with three active pits. Almost all of the coal is supplied to the 2200 megawatt Colstrip Power Station, which is located close to the mine and was built to burn the Rosebud coal.
The Colstrip Steam Electric Station, operated by PPL Montana, produces enough electricity to supply approximately 1.5 million homes. The plant burns the coal to heat water into steam, which powers the turbine generator creating electricity. A large system of concrete drainage channels carry the excess water to a retention pond at the facility.
Total Asphalt Repair Inc., in Billings, Montana, won a contract that originally called for the handforming of nearly 5000 feet (1524 m) of drainage channel at the electric station. The profile called for a channel with a seven foot (2.1 m) wide and 10 inch (254 mm) thick floor, and 40 inch (1016 mm) tall side walls. The channel has to be built strong enough to withstand the constant dynamite blasting and subsequent earth movement.
“When we first started on this project, we handformed 400 feet (122 m) of the channel which took six weeks to accomplish,” Matt Costello, owner of Total Asphalt, said. “Then, one night I looked at my superintendent, Del Aparicio, and we were both exhausted from handforming all day, and I told him there has got to be an easier way to do this.”
Their search for an easier way led them to the World of Concrete trade show in Las Vegas, Nevada, and into the GOMACO booth where they were introduced to Jim Hayward, GOMACO’s Western District Manager.
“I’ve known the GOMACO name since way back,” Costello said. “That’s all I’ve heard is GOMACO. I know there are other brands out there, but when Jim Hayward gave us the service we needed, that cinched it right there. He spent a lot of time with myself and the engineer with the power plant making sure everything was just right.”
Total Asphalt went about purchasing a reconditioned machine from Godbersen Equipment Company (GEC) and special channel mold even though slipform paving at the power plant was not yet approved. The only way to gain approval was to slipform a test section, allowing plant officials to see the slipform paver work and then test the results. The plant agreed to an approximately 250 foot (76 m) long test run. The results would determine if Total Asphalt would be able to slipform the rest of the project, or go back to handforming.
The days leading up to the test pour were busy ones for Total Asphalt. Costello traveled to Ida Grove, Iowa, for a final inspection of his GT-6300 with channel mold attached. As that was accomplished, an 18 foot (5.5 m) wide trench was being excavated at the power plant to accommodate the GT-6300. The trench was dug as an extension of an existing channel. Then, the GT-6300 was moved into position and the test could begin.
“The feeling of butterflies in my stomach just kept building and building up to the day of the pour,” Aparicio said. “Finally, the day of the pour arrived and it was good, and we knew the second day would only get better. And then we were able to breath again.”
The company didn’t conduct any test pours before taking the machine on site. They simply drove the GT-6300 into the trench, ordered the concrete, and started slipforming for the first time in the history of Total Asphalt Repair Inc. Hayward, from GOMACO, was on hand during the pour as well, to help with any potential issues.
“We were learning fast and hard,” Costello said. “We had a bit of a learning curve with the slump of the concrete and getting the mix to feed out of the ready-mix trucks. We poured a 4000 psi (30 MPa) concrete, which is a six sack mud in Montana."
The water channel is slipformed over steel reinforcing, with three rebar inserted into the wall of the channel on each side of the profile. Behind the GT-6300, finishers work with hand floats and then apply a light broom finish to the surface.
“We just had to get past the fear of slipforming and using the machine for the first time,” Costello explained. “After that, it was really a rather simple process. The machine does the work for you and you just ride along. It is really impressive to watch this machine work and do as good of a job as it does.”
Officials and engineers at the power plant were impressed, too. So impressed, that they are allowing Total Asphalt to slipform the rest of the water channel for the contract, as well as more channel projects in the future. Not only will they be busy at the power plant, but they are also considering other applications for their GT-6300.
“We’re going to start changing from asphalt over to concrete and are looking into different applications,” Costello said. “They’ve got a lot of bike trail around the city of Colstrip that would be great for slipforming. There’s also a lot more canal work to be done and by investing in this machine and mold, we’ve put the company in a good position to acquire that work.”
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The water channel’s large profile was designed to withstand ground movement caused by dynamite blasting from a nearby surface coal mine complex.
Matt Costello met with Jim Hayward at GEC in Ida Grove, Iowa, to inspect the channel mold and to review final details of the project before delivery.
Three strands of rebar are inserted into each of the sidewalls through the front of the mold.
After the pour, the GT-6300 is lifted by crane out of the trench dug for the new water channel.