The Biggest Shotcrete Job in America August 1999

With more than 7,000 cubic yards (5,352 m3) of shotcrete to be used for slope reinforcement in the Mesa-Payson Highway expansion in Arizona, it may be the biggest shotcrete application in the country, said Shotcrete Specialties.

The project consists of shotcreting 13 freshly cut mountainsides in the Kitty Joe Canyon of the Matazel Mountain Range on Highway 87 between the cities of Mesa and Payson. The total cost of the 17-mile (27.4 km) road expansion is $55 million.

"The entire project will take more than seven months to complete," said Mickey Garner, president of Shotcrete Specialties, the sub-contractor. "And we'd be done if it hadn't been for a freak late spring snow," she said. The area had about 3 feet (0.9 m) of snow just as the company was starting the project.

She said another reason the project is taking so long is that they have to follow other contractors who are doing the blasting and dirt removal. "The terrain in that area is a mixture of loose rock and dirt, which can cause unstable conditions for the construction crews." She said they had some dirt and rockslides already, and although no one was injured, it has slowed down the project.

After a mountainside is cut away, Shotcrete Specialties' crews place a drainage fabric against the rock wall to prohibit water build-up. Then wire mesh is placed over the surface. This is held in place by anchor plates, which are secured by soil nails. The soil nails are usually bolts that can go into the soil or rock up to a depth of 3 feet (0.9 m).

A 12-inch (7.6 cm) coat of shotcrete is then pumped onto the wire mesh at the rate of 60 to 70 cubic yards (46 to 54 m3) a day. The shotcrete mix used is 4,000-pound strength, specified by Arizona Department of Transportation (ADOT), but there are no special additives required.

Garner said they primarily use a Putzmeister Katt-Kreter™ pump, but they occasionally switch to the smaller Putzmeister Thom-Katt® TS 2040 trailer pump. "It depends on how long the run is," she said. "If we're pumping mud for a distance of 200 to 300 feet, we'll use the Katt-Kreter because of its greater pumping power. In areas where the run is less than 200 feet, we'll probably go with the Thom-Katt." She estimated the Katt-Kreter will be used about 60 percent of the time and moved to other difficult jobs when not needed on this project.

The Putzmeister Katt-Kreter is powered by a 101-horsepower (75 kW) engine and can pump up to 50 cubic yards (38 m3) an hour. Garner said the crews also like the Katt-Kreter because of its twin-shifting cylinders, which allow the pump to cycle smoothly. "A smooth operation makes a long day shorter for the nozzleman."

Even though the shotcrete is pre-colored a reddish brown to match the rock, ADOT wanted it to look authentic. "We carve it using knives and trowels to give it the appearance of a natural rock surface," she said.

While it takes only a crew of six to apply the shotcrete, it takes 12 people to carve it. "They have to do it when it's still moist and workable," said Garner, "and then still work fairly fast before the mixture sets." Shotcrete Specialties hopes to complete the enormous shotcrete job in November. ADOT said the entire divided four-lane highway project would be completed in the spring of 2001.

Customer: Arizona Department of Transportation General contractor: Joint venture between Meadow Valley Contracting, Phoenix, and R.E. Monks Construction Company, Fountain Hills, Ariz. Subcontractor: Shotcrete Specialties, Gilbert, Ariz. Equipment: Putzmeister Katt-Kreter™, Thom-Katt® TS 2040