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Set in Concrete
Posted By admin On September 1, 2012 @ 7:00 am In Articles,Featured Articles,Features,Plant Profile | No Comments
Arrowood Quarry was a standout, in more ways than one, during AGG1 this year.
By Kerry Clines, Senior Editor
Martin Marietta Materials’ Arrowood Quarry located in Charlotte, N.C., started out as a portable plant in 1965. The permanent plant was built soon after in 1968.
During AGG1, Arrowood Quarry opened its gates to interested show attendees. A bus tour took visitors through the entire operation, from the pit to the processing plant to the loadout, and everyone was treated to viewing a blast. Those who were unable to attend the tour missed getting a glimpse of what makes this operation unique.
Plant personnel spent many hours sprucing up the quarry for the AGG1 tour. “We started in September and painted about 80 percent of the process plant,” says John Smith, plant manager at Arrowood Quarry. “It took 3,000 gallons of paint and 10 tractor-trailer loads of sand-blasting sand. It hadn’t been painted in about 15 years.”
“The crew did a great job getting ready for the AGG1 tour,” adds Bill Podrazik, operations manager for the Carolina West Region, Martin Marietta Materials. “They’re as proud of this place as we are.”
Quarry visitors were greeted with some fairly unusual features. “The plant is kind of unique,” Podrazik says. “It’s a wet, fractionated plant. When the material hits the screen tower, it actually goes into the fractionated blending tunnel wet. Then we pull it back out and rewash it. It’s nice from the dust-control perspective.”
One of the most interesting and unique features of the plant is the loadout bin structure. It contains nine 250-ton bins — all concrete. “You probably won’t ever see concrete bins again,” Smith says. “It cost a lot of money back in 1968, and if you were to do something like that today, it would probably cost several million dollars. Steel is a whole lot easier to erect, but it won’t last. That concrete’s not going anywhere. They just don’t build structures like this anymore.”
Arrowood Quarry is located right along the border between North Carolina and South Carolina. The property covers a total of about 450 acres. Most of the acreage is in North Carolina, but part of the property is located across the border in South Carolina. “We don’t have our permit to mine there [South Carolina] yet,” Podrazik explains, “but we will have mine permits from two different states when it’s all said and done. We serve both DOTs.”
Arrowood’s pit is a little over 300 feet deep. It has been worked in benches with each bench averaging a height of 42 feet, but there’s still room to go down a couple more benches, if desired.
The geologic deposit is said to go 10,000 to 15,000 feet down and is mainly made up of a type of rock called gabbro. “The rock is somewhat unique,” Podrazik says. “Most of us call it granite, but it’s a little bit denser than granite. Specific gravity averages right at about 2.96, so it’s a pretty heavy material.”
Most of the quarry’s haul trucks have 4- to 6-inch-thick, heavy-duty rubber bedliners, which provide protection for the truck beds, extending their service life between 15,000 and 20,000 hours, Podrazik says. “We try to maintain an 80-foot-wide haul road,” he adds. “It takes up a bit of reserve space, but trucks are just getting bigger, and we don’t want the trucks held up because there’s not enough space.”
Material is hauled from the pit up to the primary crusher, which is a gyratory located above the pit. It consists of a single-sided dump hopper with a rock breaker on one side. “This is a pit gyratory,” Podrazik explains. “It’s buried in the ground. They shot around it. There’s a tunnel that comes up underneath. Housekeeping is a challenge because you have to take a spiral staircase or the tunnel to get in and out of it. Access to motors and lube systems is a bit tight, but they manage.”
Right now, the haul distance from the pit to the gyratory crusher is more than a mile because of the depth of the pit and the number of benches, but work is being done on some of the benches to shorten the haul route, which will reduce fuel usage and improve cycle times.
A 42-inch-wide belt with a 400-horsepower motor carries material from the gyratory to the surge pile. Two 900-foot-long, clean-stone blending tunnels have 36-inch-wide conveyors that run through them. One conveyor feeds the wash screen on top of the bin tower. A quaternary crusher recrushes the material into half-inch and larger, all the way up to 3s, which are ballast stones.
At the south end of the plant, a 500-foot tunnel joins the two blending tunnels underground. “Back in the day, they did some blending between the two, but the tunnel was difficult to clean, so we pulled the conveyor out,” Podrazik says. “It’s an access way and escape tunnel now.”
Only two wheel loaders are used in the plant. One operates on the yard and the other is used for stockpiling.
The plant is not totally automated as many are today. One person in the loadout control tower monitors cameras in the tunnels and brings product up from the stockpiles. A conveyor on top of the bins runs on a rail-type system that allows it to reverse and move from one bin to another. Only the pressure circuit with the bins is automated.
“That’s one of the things we’d like to do,” Podrazik says, “get this plant more automated. But automating a plant from the ’60s isn’t the easiest thing in the world.”
The primary plant can handle about 1,400 tons per hour; the secondary handles about 750 to 800 tons per hour. The primary plant has one conveyor. The secondary plant has 45 conveyors, 10 screens, and 45 feeders — 35 of which are vibrating or belt-type screens and 10 of which are gate feeders. The last major upgrade done to the secondary plant was the addition of a recrushing circuit and screen that were added in 1988.
Between the primary and secondary plants, there are more than 16 motors of 250 horsepower or greater. Nine pumps in the wash circuit — pit dewatering and slurry circuit — pull out all the wash water and recirculate it through seven settling ponds on the property.
The plant has cable-suspended stackers. They have to be inspected regularly, but they allow more room for other equipment. “You don’t have to worry about loaders banging into towers,” Podrazik says. “They give you plenty of room to stockpile in just one bin.”
Contract blasting is provided by Austin Powder Co. “They do a good job for us,” Podrazik says. “We use a down-the-hole hammer drill to drill a 6-inch hole in a 13 by 17 pattern. Average shot size is between 30,000 and 40,000 tons. The drill is used by two or three different locations, so when it gets through drilling here, it moves to another plant. We shoot electronics now, but historically, the blasts have been non-electric.”
Smith says the quarry does have rail service, but that it hasn’t been used much lately. “We don’t load a lot out by rail currently,” he says, “but we have that potential.”
Stress on safety
“Martin Marietta prides itself on safety,” Podrazik says. “In our industry, everyone is improving on it every day. At this location, the last lost-time incident we had was 600,000 man-hours ago in 2001. The last reportable we had at this location was in 2006.”
Arrowood Quarry has an internal safety center that is used by everyone at the plant. The center features an overhead projector in each room, allowing easy access to safety information for all its employees.
“The hourly folks use it for doing their safety observations, putting in near misses, and for access to any kind of safety information,” Podrazik says. “It’s readily available and is online. We’ve got an internal safety computer system within our division that can be accessed, as well, to see what’s going on around the division and the industry. With technology being the way it is, the more information they have, the better off they’ll be, especially from a safety standpoint. We all know that if it has happened here, it has probably happened somewhere else. If we can learn from someone else’s near miss, we try to take advantage of that.”
Dealing with the slow economy
Arrowood currently employs 18 hourly and four salaried employees. “This year, we’ll probably do just short of 1 million tons, which is actually an improvement over where we’ve been recently,” Podrazik says. “During the peak in 2007, it was just below 2 million tons.”
Last year, the plant only ran for about five months out of the year. “We didn’t lay anyone off,” Smith says, “we farmed them out to different places. They had to drive a bit further, but we paid their mileage, and they, at least, got to work. The only market we have right now is a concrete stone and asphalt stone. There’s lots of resurfacing and concrete work going on, but no new road construction for our base stone.
“Business is better than last year, but not by much,” Smith adds. “The forecast for 2013 is looking better than this year, so business is changing to the positive side. The new transportation bill has not made an impact on this operation yet, but several big projects are coming up for bid.”
Kawasaki 135Z4 wheel loader
Caterpillar 988H wheel loader
Caterpillar 773B haul truck
Caterpillar 775E haul truck
Caterpillar 775F haul trucks (2)
Komatsu PC-300HD excavator with NPK G18 hammer
Atlas Copco L6H down-the-hole drill
Volvo G710 VPH motorgrader
Allis Chalmers 42 x65 gyratory crusher with
NPK GH10 B6500 pedestal breaker
Nordberg 7-foot standard crusher
Nordberg 7-foot shorthead crusher
Excel Raptor 400 shorthead cone crusher
Nordberg HP-300 fine cone crusher
Deister 6 x 16 three-deck wash screens (4)
Deister 6 x 16 three-deck dry screens (3)
Deister 6 x 16 two-deck dry screen
Deister 6 x 20 two-deck rinse screen
Deister 4 x 10 single-deck wet sand screen
GIW 6- x 8-inch LSA25 slurry pump
GIW 6- x 8-inch slurry pump
Eagle 54-inch twin sand screw
Plant support equipment:
JLG 80-foot manlift
John Deere 310SJ backhoe
Terex BT4792 boom truck crane
Caterpillar 980G wheel loader
Caterpillar 980H wheel loader
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