photos by William Weaver
Dave Nall, Quality Control Manager for the asphalt side of the Galesburg, IL asphalt and concrete recycling Gunther Plant, a division of United Contractors Midwest (UCM), has this sign on the wall of his office: “Quality Control always costs less than Remove-Replace.” Nall and the rest of his crew are firm believers in that statement.
For Nall, quality control involves many steps. “We design our own mixes,” he explained. Up until about 20 years ago, the State of Illinois handled all the quality control. Since then, contractors have been responsible for quality control within their own company. This allows companies more leeway in finding and using less-expensive material. All materials used at the plant come from within the state, except for a small amount of material that comes from just across the river in Iowa. “We’re not locked in to a given supplier,” he said.
“The first step in quality control is checking the gradations of the material we receive from the quarries to make sure they’re the same gradations we used when we originally designed the mix,” continued Nall. “We check the gradations with a set of small screens and a small vibrator. Our aggregate is mostly dolomite, and ranges in size from ¾” to a coarse 3/8 inch. The main problem we find is too many ‘fines’ in the aggregate mix. The quarries all have quality control in place, so 9 times out of 10, they meet the specs.”
A typical design might be 60% aggregate, 35% sand and recycled asphalt product, (the per cent of that varies with the mixes), and 5% oil.
Recycling takes a powerful crusher, and they do it on site. “Our main machine is a JW Jones Impact Crusher. That machine has taken tremendous punishment over the years, crushing both asphalt and cement, and it just keeps on running.”
Since cleaning out the impactor is time-consuming when there is a change in materials from concrete to asphalt and back again, a Prosizer, is brought in to crush the asphalt to avoid downtime for crusher cleaning. From the crusher, the recycled asphalt is conveyed onto a shaker screen to size it.
Manufactured sand is the preferred type of sand at the Galesburg plant. Rock is crushed for sand rather than using natural sand. “Manufactured sand is angular, not round-grained like natural sand. Angularity is very important for asphalt. The angular-shaped pieces lock together and stay in place better than round sand grains would.”
The oil is the one ingredient in the asphalt mix that is not tested at the plant. ”We don’t test it because we don’t have the right lab equipment. Asphalt cement samples are taken from our storage tanks and sent to IDOT for testing.”
“In Illinois, to minimize cracking in road asphalt under extreme weather conditions, we use oil that has synthetic polymer additives incorporated into it to give the mixture more elasticity. Several different polymers can be used, depending on the average temperature highs and lows of the area in which the asphalt will be applied. The polymer additives will be different, for example, in northern Illinois from those used in southern Illinois. We can get extreme temperature changes. In the summer, the asphalt really absorbs the sun’s heat, and in winter, temperatures can plummet. The elasticity the synthetic polymer additives give to the oil to make it more pliable is very useful under these conditions.
Although each company designs its own asphalt mixes, the state of Illinois checks the results. “IDOT tests at least 20% of our samples. When we take a sample, we split it in half. We check one-half and save the other half for the state. We have parameters for how close our results have to be to the state’s, or it will raise a red flag.
“In actual practice, we often sample 2 to 4 times daily to make sure we’re getting the results we need. If the results are good, we keep running that mix. But it’s like life. It’s not going to be perfect every time. When we run into problems, we make adjustments as we go. We’ve been trained in spotting problems and heading them off.”
“Our most common problem is too many fines in the mix. If we don’t correct that, it usually leads to rutting in the asphalt road bed after a few years. A trench will develop from tire wear, and will collect water when it rains. This can result in hydroplaning.”
“If we run into real bad problems, we shut down for the day and keep on troubleshooting, but 90% of the time, all we need to do is make minor tweaks in the mixture. Sometimes the gradations change unexpectedly. Most of the time, though, we can adjust by adding different materials.
“Our asphalt plants are all computerized, and set up to add a certain percentage of each material. The first thing we do when we get ready to fire up each April is calibrate the plant, so when we program it to put in 15% of a given ingredient, it will actually be putting in 15%. We calibrate once a year. (The plant closes for the winter at the end of November.) Most of the time, the calibrated plant is ‘dead on the money.’”
“Problems with the computer system don’t happen often, but we sometimes find that a minor part is not working correctly, or there might be a short in a wire so a signal from the yard is not getting relayed properly. The guys who run our plant know the plant from head to toe. We know how each individual component is supposed to function. With minor computer problems, any one of us can make the correction. The only time we’d need to call in outside help is if something would go wrong with the central computer.”
The Galesburg plant is a continuous flow drum plant. After the aggregate, sand, and recycled asphalt weighed, mixed and dried, a flame shoots through the big burner and heats the material. Then oil is injected into the mix, and it is stored in two heated and insulated silos. “We can hold finished asphalt through the day, but we don’t store it overnight.”
The final quality control step takes place at the job site. “We monitor how the asphalt runs through the paver and monitor the rolling and compacting.” Nuclear density gauges are used to check the compaction. There are certain standards we’re shooting for on the amount of compaction with the mixes. This is a big quality control parameter.”
The Galesburg plant has been fueled by natural gas for the past 5 years. “We used waste oil as our fuel for a while. However the cost of waste oil kept rising, and there was a lot of variability in quality from shipment to shipment. It was a temperamental product that couldn’t be counted on to give an even flame. We’ve found there are a lot of advantages with natural gas.”
The last couple of years, the asphalt industry has been down in Nall’s area. In a normal year, the Galesburg plant produces about 60,000 tons of asphalt, and about 15% of that uses RAP. The day we visited the plant last winter, there were large piles of broken asphalt waiting to be recycled.
United Contractors Midwest (UCM) has 16 asphalt plants, from Bloomington to Decatur in the southern part of the state. They also have a division in Missouri.
In recent years, recycled concrete has probably been the Galesburg plant’s biggest sellers, with about 25,000 tons of 100% recycled product produced each year. The plant employs six to eight people in-season, and a small staff, including Nall, through the winter.
What kind of savings are realized by using the recycled asphalt in the mix? “The savings depend on the particular mix you are running at the time and the total volume of recycled product you’re using. The average savings at this plant are probably in the ball park of 15 to 20 %,” estimated Nall.