At the Marine Corps Air Station, Miramar, Calif., several concrete forming and finishing challenges were part of the design/build Osprey MV-22 taxiway expansion, parking apron additions, and hangar construction. The project is an $85 million joint venture between Hensel Phelps Construction and Granite Construction.
The Osprey MV-22 is a Short Take-Off and Vertical Landing (STOVL) aircraft that generates high exhaust temperatures so great that conventional portland cement concrete (PCC) cannot withstand the extreme thermal loads. The development of high-temperature concrete solved the problem of deteriorating PCC pavements caused by STOVL aircraft. The high-temperature concrete used on the project incorporates an aggregate known as trap rock, which is naturally fire-resistant and combines firmness with an ability to bend instead of breaking when under pressure.
According to Granite engineer Justin Seichter, “The slump was around 2 inches for the project and the specs require a zero edge slump. With this special mix, there were concerns about meeting that spec while slipforming, so we set steel forms to control and ensure a vertical edge.” About 6,000 lineal feet of ¼-inch DUAL Paving Forms (14x12-inch and 14x11-inch) were provided by Metal Forms Corp. to place the 14-inch-thick pavements.
Using forms did not prevent Granite from using its slipform crews and equipment. The company’s G & Z slipform paver was first used to place the high-temperature concrete by straddling the forms and placing separate pavements that were either 30 feet or 34 feet apart. Once the original slabs were set and cured, the slipformer traveled on the existing pavements to place and finish the 30-foot and 34-foot gap sections.
The Miramar project was completed in the fall of 2013. Some of its most sustainable features include 1.3 million square feet of recycled concrete and asphalt, which will generate 73,000 tons of aggregate used in the base support of the new high-temperature concrete aprons.