Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/282830
AGGREGATES MANAGER April 2014 12 most areas. Overburden is minimal, usu- ally no more than 3 feet. "We run two 10-hour shifts on all the plants," Snead says, noting the first shift begins at around 5 a.m., with a shift change between 2:30 and 3 p.m. "It's a full change out. We rotate everyone. The drivers and operators have to change. We've always shared the operating equip- ment between the two shifts because it is expensive, so two school buses make the rounds dropping off and picking up at shift change. The second shift works till about 1 a.m. So, we run, basically, 20 hour days with 100 hours of production a week." The quarry has approximately 112 employees, 40 of whom work nights. "We do a lot of loading and shipping during the day, but we don't do that at night," Snead says. "Maintenance is a big part of the business, so about 25 percent of our employees are doing maintenance. It's easier to do our maintenance during the day, because we can order parts and get answers to our questions. That's why we run at night." Blasting usually takes place one or two times per day. At the primary plant, the material is crushed, and base material is screened out and sent directly to a stock- pile. There, samples are tested for strength and gradation, and must be approved by the city of Austin. The oversize material is crushed again to produce graded aggre- gate, which is placed in stockpiles over a blending tunnel. Customer trucks are loaded from the stockpiles. The loaders are sized so they can load a trailer truck with two passes and a smaller dump truck with just one pass. Trucks move in and out of the quarry quickly. Once loaded, they proceed to the scalehouse located on the George- town side of the quarry. The scalehouse is elevated, providing a bird's eye view of customer trucks as they approach the three scales. Each truck pulls onto one of the scales to check its weight. If the weight is good, the truck will pull under the scale- house where a ticket is sent down a chute to the driver. If the truck is overloaded, it is sent to a Barko, which is a specific type of material handler. It is usually used in forestry work to pick up logs with a grapple, but in this case, it uses a bucket to remove excess aggregate. "We try to turn the trucks in and out in less than 15 minutes," Snead says. "The trucks are worth about $1 a minute, so the faster we can get them in and out, the bet- ter they like it. On any given day, we have a truck through the scales about every 12 seconds or so, up to about 2,000 trucks per day. The mornings are always busy with the first round of trucks. Then it kind of flows in groups after that." Rail transportation There are two separate loadout systems for railcars. One is for base material, which comes directly from the primary crushing plant. "The material is screened, blended with a certain amount of fines to control gradation, and then sent out to an over- head bin on a belt scale that weighs it as it moves along," Snead says. "We try to fill the overhead bin with enough material to fill three railcars at a time." The railroad track runs under the overhead bin, and the railcars are pushed along by a locomotive with an operator at its controls. After the railcars are loaded, they are weighed again by a vehicle-in-motion scale to make sure the weight is correct. The primary plant on the Round Rock side of the quarry is connected to the secondary plant on the Georgetown side via a 2-mile-long conveyor.