For example, a coarse mix with a lower percentage of sands and fines will require less heat because it will have less moisture in comparison to a finer mix, which is dense employing higher amounts of sands and fines, therefore more moisture. “When you combine the mix type and increased recycled materials, which innately have higher amounts of moisture, you’ll have to adjust your burner accordingly,” says Bartoszek.
Once the burner is set, double-check the temperature of what your mixing is very close to what is getting loaded out. “The quickest correlation anyone can use to ensure that you don’t have moisture in the mix is to check the temperature of the product you’re shipping out,” says Bartoszek.
For example, if you have a mix that is produced at 330 degrees, ensure the moisture is out of the mix and optimize the flame so you’re not producing at 340 degrees. When the material is loaded in the truck, make sure there hasn’t been a 15- to 20-degree drop. “If there’s a large temperature drop between production and load out, you probably have moisture in your mix, your plant is not running efficiently or the materials are too wet,” says Bartoszek. “You might have to slow the plant down. If it’s running too fast or not hot enough, you’ll have moisture in the mix and you’ll see the change in the temperature.”
Communication between plant operators and paving crews is another way to keep an eye on your mix temperature. “There are intangibles that happen out in the field, and there’s no gauge we can put out there that says this material is dropping too fast,” says Bartoszek. “That kind of temperature drop would mean there is a severe problem, but points out that paving crews and plant operators have to communicate effectively. Are the temperatures correct once the material arrives in the field? Constant communication is as critical to optimizing your plant as the components you’re installing to ensure accuracy.”
There are a few components and technologies that Bartoszek says are “must haves” when it comes to running an efficient asphalt plant.
RAP crushers. “Correct flow is crucial to an efficient production process,” he says. “A lot of suppliers offer a RAP crusher or nugget cruncher that handles the oversize pieces that sometimes come from recycled materials.”
RAP crushers crunch the material so there are no oversize pieces restricting or stopping material flow to the drum. Installing this type of component is a great process control technique, says Bartoszek. “RAP crushers really ensure oversized or large pieces of conglomerate are not entering into the plant,” he says. “If these pieces end up in the mix, it can really affect paving quality. Oversize chunks in RAP will create a bump in the mat, and smooth pavements are extremely important to paving contractors.”
Bins are another component to pay close attention to. Multiple RAP bins help with versatility, and RAS bins should have steeper slopes and wider throats to ensure the material flows and isn’t clumping during the feed production process.
Reverse weigh bridges. An asphalt plant can install load cells or a weigh bridge directly on the belt to make sure the weight is accurate. This also helps you receive real-time feedback that you have the correct amount of materials going into the process. “With recycled materials, you have a tighter tolerance than you would have with virgin aggregates, so the weigh bridge helps with accuracy,” says Bartoszek.
Longer drums. Counter-flow drums with extended mixing zones is something the industry is moving toward, says Bartoszek, because of the increased amount of recycled products now being used. “For producers using high amounts of RAP and RAS, we’re already seeing and using this trend at our plants,” he says.
“We don’t want to waste fuel by superheating aggregates,” he explains. “Right now, we superheat the aggregate to aid in the drying of the RAP and RAS, but superheating those aggregates is wasting a certain amount of energy. By lengthening the drum, you don’t have to superheat the aggregate as much because the materials have a longer drying time.”
A longer drum can also give the plant better capacity.