For one reason, the plant won a National Asphalt Pavement Association (NAPA) Ecological Award for New HMA Facilities. "We're very pleased," says Kelly, executive vice president of Walsh & Kelly Inc., a paving contractor based in Griffith, Ind.
"Credit goes especially to Rich Wise, our plant superintendent, and to the people at CMI Corp., the manufacturer. It's a well designed plant, and we've all given the attention to details it takes to make the facility a winner."
And, as Wise says, the new plant gives Walsh & Kelly a definite edge in making hot-mix asphalt (HMA) under the Superpave design system.
Good thing, because through 1996, Indiana had placed the nation's second highest number of Superpave tonnages-494 tons-behind only Colorado. Last year Indiana switched entirely to PG binder grades and is in the process of specifying all HMA with Superpave.
Not only is the South Bend facility built for high production, its four vertical AC tanks and eight cold feed bins give the plant quick-change versatility unmatched in northern Indiana. The plant is a CMI STD-400 Triple-Drum Counterflow Drum Mixer with 400-tph capacity.
Included are three 300-ton HMA storage silos; eight 32-ton cold-feed bins, four 20,000-gal vertical AC tanks and pumps to match; one 32-ton RAP bin; and an RA-320 Roto-Aire bag house.
The new plant opens
Plant mix first hit the trucks last August, when the facility replaced an aging 200-tph batch plant. Richard D. Vick, Walsh & Kelly president states, "This new plant runs an excellent quality of mix. It emits less dust and runs much more efficiently than our old plant."
As for NAPA's opinion, the following are some factors the judges used to name the plant a winner:
- Use of a gas analyzer to control combustion efficiency;
- A water pit to control dust from aggregate stockpiles, pavement over the site, and water hydrants for facility wash-downs;
- plan to prevent or counterattack spills of fuel or AC products; and
- Use of approved truck-bed release agents.
Kelly expects the new plant to provide a substantial production increase. Much of the company's HMA tonnage from the new plant goes for street and highway construction. The company also sells HMA for commercial and industrial developments.
This year, the new plant will provide the capacity for Walsh & Kelly to add one or two paving crews based at South Bend. "We now have double the available capacity-and the flexibility to make more mixes on demand-than we had with the old plant," says Kelly. "In 1998 we expect a good amount of work from the government agencies and continued growth from the private sector," Kelly added.
Handles Superpave
Unlike dense-graded Marshall mixes, asphalt designed with Superpave relies heavily upon one's control over the volumes of aggregate going into the mixture. Success with Superpave depends on meeting specifications such as voids in the mineral aggregate and voids in the total mix. "Being able to handle the fines more accurately is an issue," says Wise. "If you can't get a good handle on fines, your mixes will not meet spec."
Fine control is one reason Wise says he likes the new plant. "We used to run fines in the 3% to 4% range. Now we're usually running fines at 5% to 6%." The amount of fines plays a basic role in controlling voids in the total mix. And that is trickier with Superpave, because such mixes run leaner on the sands and mid-sized aggregates that used to fill up the voids.
"That's why we went with a dust silo and weigh pod under it. We actually weigh the fines back into the mix. It's called a negative weigh system," says Wise. "The silo fills the weigh pod and the plant's Impulse system monitors the weight of the pod as it feeds fines into the mix. By weighing the amount left in the pod, the system calculates the amount going to the mix, and we get a read-out of that in the control house."
The plant's ability to control the fines in HMA mixes is not its only Superpave advantage, says Rich Wise. With four AC tanks, the company can store four different PG grades of asphalt cement, and be ready to use them at a moment's notice. Plus the eight cold feed bins, 32 tons each, add to the plant's flexibility. "We were always limited to two kinds of mixes, because of our storage and asphalt tanks," says Kelly. "Plus we can greatly reduce our operator time for the same production. Before, we would have had to start at 3:00 or 4:00 in the morning for a big production day. Now we can hit the ground running in the morning and stay with the pavers all day."
"I like the RAP system on the plant," says Wise. "I'm real fond of the variable frequency controllers on the electric motors that drive the RAP cold feed conveyors. And the AC system is driven by variable frequency power, it's not like the old eddy current driver.
"We've really not had any segregation. With the controls we can vary the times when the batches empty at the top of the silos, and that pretty well defeats segregation."
