Crushing fleet generating added revenue for construction company

In the foothills of the Great Smoky Mountains, a major asphalt and concrete contractor is using impact crushers to accelerate production of processed reclaimed asphalt pavement (RAP) and recycled concrete aggregate (RCA), while using jaw crushers to process virgin aggregate.

With these crushers – all of which are Kleemann made – Harrison Construction Co. is realizing gains in productivity and ease of mobility.

Harrison Construction, which is a division of APAC-Atlantic, has provided ground-level site construction throughout eastern Tennessee and western North Carolina since 1947. The Harrison Asphalt Division specializes in private, residential and commercial asphalt paving, with a total of 22 asphalt plants that manufacture mixes for highways, streets, driveways, parking lots and bicycle paths.

The Harrison Quarry Division operates seven quarries, plus a sand plant and aggregate sales yard, all of which provide crushed stone and aggregate products. It also operates 12 concrete plants and a fleet of 60 ready-mix trucks.

“I look for new avenues of revenue for Harrison,” says Cale Cameron, specialty materials manager at Harrison APAC-Atlantic who is responsible for mobile crushing, landscape materials and free-on-board sales of hot mix asphalt for eastern Tennessee and western North Carolina.

Twelve asphalt plants in this territory own and rent Kleemann Mobirex impact crushers that process RAP. Asphalt plants that don’t run continuously also exist, and Cameron moves his MR 110 Z EVO crushers around these plants as needed.

In a year, Harrison crushes about 350,000 tons of RAP and 60,000 tons of RCA.

“Kleemanns are the only crushers we have,” Cameron says. “We move them from plant to plant. In Tennessee we crush RAP and reclaimed concrete aggregate from demolition concrete. And we have quarries in North Carolina where we crush virgin aggregate, but also crush asphalt there.”

Varying applications

Late in 2015, Harrison was crushing RAP at two locations, using a Mobirex MR 110 Z EVO crusher paired with an MS 19 Mobiscreen to process RCA at its Spring Hill location outside Knoxville, Tennessee. Harrison was also using an MR 110 ZS EVO to crush RAP at its Hendersonville, North Carolina, plant.

“At Spring Hill, we are taking demo material from the University of Tennessee-Knoxville campus – where they are tearing down a lot of buildings – and using a Mobirex impactor with a Mobiscreen to crush and screen recycled aggregate,” Cameron says.

These units were sold or rented from Bramco-MPS in Louisville, Kentucky.

“Other brands of machines were closer,” Cameron says. “But we are partial to the Kleemann machines because of their superior uptime.”

To crush concrete there, the standalone mobile screen was used instead of the attached screening unit seen on Kleemann “S” models.

“We found that with concrete from a demolished building, including all the aluminum and wood – anything nonmagnetic – the separate screen works better than an attached screen, because the pieces may get snagged inside its twists and turns,” Cameron says. “This applies to all makes of crushers. But if your concrete is very clean, or if you are crushing RAP, the attached screen is no problem at all.”

Harrison also uses Kleemann mobile crushers for primary crushing of virgin aggregate.

“In our Waynesville Quarry we recently crushed granite with an MC 110 (jaw) crusher, in the cut,” Cameron says. “We backed it up against the shot highwall and crushed the stone. That crusher-run aggregate was dumped in a hopper and slid down an HDPE (high-density polyethylene) pipe to a stationary plant where it was processed further.”

Abandoned in-line crushers

In Hendersonville, Harrison used its new MR 110 ZS EVO mobile impactor to process RAP instead of an in-line crusher.

“With Tennessee DOT (Department of Transportation), if we process the RAP to the right size and spec, we can return a higher percentage of RAP back into the mixes,” Cameron says. “We’ve tried in-line crushers in our plants, but nowadays, the DOT allows more and more recycled asphalt into the mixes, and in-line crushers just can’t keep up. But if we run mobile impact crushers instead we can get better production at a lower per-ton cost.”

The DOT accepts up to 15 percent RAP in surface mixes, and up to 30 percent in base mixes, Cameron says.

“In Tennessee we crush a 5/8-in.-minus RAP particle, and in North Carolina we do 5/8-in.-minus and some 3/4-in.-minus for base mixes,” he says.

With a crusher inlet opening of 44 in., the MR 110 can take nearly anything thrown at it, Cameron adds, and that’s great for productivity.

“If there is waste material at the plant, or the customer brings in large slabs of asphalt, you could not do anything with them with the in-line crusher,” he says. “You’d have to pre-crush it anyway, so we might as well have the bigger crusher to start.”

Both of Harrison’s MR 110 Z impactors incorporate effective primary prescreening by means of a double-deck screen incorporated in the feed system. This prescreen removes fines ahead of the crushing circuit and either sorts them off to the side or reintroduces them to the crushed material where they become part of the final product.

“The prescreen is a significant advantage for us,” Cameron says. “Anything that doesn’t go into the crushing chamber reduces wear inside the chamber, and that’s a huge bonus. On top of that, the material doesn’t take up space on your primary screen deck. We like to pull all the fines out ahead of the crusher, because we see the fines producing a lot of wear, on the blow bars and the bottom of the toggle plate.

“At one of our plants, we ran a tracked stacker right next to the prescreen, and the screened fines went into the tracked stacker, bypassing the whole crusher,” Cameron says. “The stacker put those fines back onto the main belt, blending it with what had gone through the crusher, and saw a 15 percent increase in production while keeping 80 to 100 tph out of the crushing chamber.”

Zero-gap setting

Whether equipment is owned or rented, Harrison settled on the Kleemann platform for its crushing needs because it works for them.

“We looked at three or four different brands of crushers, and stumbled on Kleemann,” Cameron says. “I visited the facility in Nashville and my first impression was the professionalism of the people I met. I was overwhelmed by the way the machine looked.

One of the biggest Kleemann advantages is in its electronics, he says.

“If a piece of rebar gets hung up, the machine shuts itself down instead of tearing itself up,” Cameron says. “You don’t have hydraulic pumps trying to keep working with the rest of the machine stopped. And the Kleemann tells you what’s wrong; you don’t spend 30 minutes looking at it trying to figure out why it stopped. You open the two doors, and look at the code on the panel.”

A case in point of the advanced technology of Kleemann’s impact crushers is the fully automated hydraulic adjustment capability of the crushing gap, which permits greater plant uptime, while improving quality of end product, according to Kleemann.

Not only can the crushing gap be completely adjusted via the touch panel electronic control unit, but the calculation of the zero-point is possible while the rotor is running. This ability to accurately set the crusher apron from the control panel with automatic detection of zero point and target value setting saves time and improves the overall efficiency and handling of the crusher.

“An example of the controls is adjusting the gap setting of the impact crusher,” Cameron says. “We used to spend at least 30 minutes a day adjusting our old crusher, dragging out tools, turning bolts and beating the thing and sweating. Now there is no problem dropping in whatever they want the setting to be. We don’t have to use shims as gauges, and we don’t have to open the side inspection door and measure that setting each time. It would be difficult and time consuming and frustrating.

“If the gap opened up to an inch and a half, and we were crushing 5/8 [in.] we would have to make the decision whether it was worth being down for 30 minutes or an hour to readjust, or just let it run with less production,” Cameron adds.

Now the setting is automatic, quick and precise.

“In the mornings, while the machine is going through the gap-setting process, the guys can be moving around the machine inspecting and greasing,” Cameron says. “If you want the gap setting to be a half-inch, you set it a half-inch. If you want 11/16 [in.], you get 11/16 [in.]. With the old machine, an inch might be as precise as we could get. This alone saves us two hours a week, and depending on what size screen cloth we’re running, easily 400 tons.”

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Tom Kuennen is a freelance writer specializing in the construction, energy and mining fields.