It's no secret that customers are wanting increased RAP (reclaimed asphalt pavement) usage in mixes and are in need of the equipment to give them the competitive edge, especially in large metro areas where RAP is in good supply. Coupled with diminished money available for projects, cities and states are trying to get the most out of the funds available by looking for ways to counter the high cost of asphalt and still maintain the quality of material.
Meeting The Need
Astec's innovative drum designs are able to provide customers with the equipment to meet their RAP needs. Whether it be zero or 100 percent RAP, Astec offers the following:
- Nomad: 0% RAP
- Voyager 120: 0 to 30% RAP
- Unidrum: 0 to 40% RAP
- Double RAP 120: 0 to 40% RAP
- Double Barrel: 0 to 50% RAP
- Double Barrel HR: 0 to 65% RAP
- RAP King: 100% RAP
According to Malcolm Swanson, president of Astec, Inc., the cost of asphalt is more likely to increase, rather than decrease, over time.
"There's a serious need to be able to use as much RAP as possible without sacrificing the quality of produced materials, Swanson said. "To be able to build a quality road using RAP (using high-RAP percentages) and still meet air pollution limits (that's one of the issues with using high-RAP percentages in mixes) are vital to being cost-effective on all fronts."
Astec is working on solutions in response to the situation concerning emissions by enhancing its equipment to be capable of using higher-RAP percentages, while maintaining production of quality materials.
The Astec Double Barrel® has been a key component in the production of material using RAP. Since its beginning, the Astec Double Barrel® has been capable of producing 50/50 RAP mixes. But with the need for increased RAP usage, Astec has answered the call by enhancing the Double Barrel® to use up to 65 percent RAP. A totally new drum, the RAP King, makes 100-percent RAP mix.
"Astec currently has a plant operating in the 60 to 70 percent RAP range," said Swanson. "It's a Double Barrel® that we have enhanced to use higher percentages of RAP."
According to Swanson, a key element of being able to run higher percentages of RAP is to be able to control the baghouse temperature.
"Over the last two to three years, Astec has developed a system that controls baghouse temperature and is able to do so with considerable independence from production rate, burner firing rate, and mix type," said Swanson. "This is accomplished by drum speed changes and V-flights; dubbed the patent-pending V-Pack™ Stack Temperature Control System."
Swanson continued: "Standard flights tend to produce a less-than uniform veil. Having holes in the veil can be an issue when running RAP due to less material in the drum. It's very important when running high percentages of RAP that the virgin aggregate be uniformly distributed in the drum to allow heat transfer. When this does not happen, the baghouse overheats."
The Perfect Laboratory
Astec has a host plant in service in New York City using the V-Pack system. The plant is the perfect laboratory for Astec's new system, making high-RAP mixes routinely. Using the Astec system, this plant has made mix with as much as 70 percent RAP.
"In the same plant in New York City, using the Astec system to control baghouse temperature, the operators are able to make 100-percent virgin mixes and high-RAP mixes without having to make any physical changes to the plant," noted Swanson. "The plant can handle the mix changes without difficulty. The patent-pending V-Pack™ Stack Temperature Control System is able to control the drum speed to control veiling."
The problem with running both types of mixes in a plant has always centered on flighting. The flighting for RAP mixes is designed to avoid overheating the baghouse. When using the same flighting for virgin mixes, condensation occurs in the baghouse. The end result of condensation in the baghouse is a buildup of mud, and replacing blinded bags is expensive.
"The V-Pack system has eliminated this problem," said Swanson. "The Astec system enables a plant to make both mixes, back to back, by changing drum speed to control veil density."
Another key element in the Astec V-Pack System is the special geometry of the combustion zone flighting. The new system is using a unique combustion zone flighting that varies from Astec's traditional design," said Swanson. "The combustion zone flights are also made of stainless steel to withstand higher temperatures associated with using higher-RAP percentages."
The RAP King will be the Astec system using 100-percent RAP in mixes. It will be a hot oil tube-based dryer. Still a rotary dryer, but instead of having direct exposure to hot gases, the RAP is tumbled over a heating element inside the dryer, keeping the RAP in a nearly oxygen-free atmosphere.
In summary, Swanson noted: "The need for more RAP usage in mixes is driving the Astec equipment evolution."
LL Pelling in Cedar Rapids, Iowa, uses Astec’s warm mix system. The Double Barrel® uses up to 50 percent RAP.
For no need of RAP, Dillman offers the portable hot-mix plant called the Nomad™.
The Astec Double RAP separates the drying and mixing process to provide reliable RAP recycling, effectively using up to 40 percent RAP.
Asphalt producer and seller Kelterite Corporation in Downey, California, stockpiles RAP.
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