P&S Paving completed the installation of a 300 TPH (272 MTPH) 8 ft x 40 ft (2.44 m x 12.19 m) Double Barrel® XHR asphalt facility in Daytona, Florida, near the end of 2015 to run up to 60 percent recycle.
Recycled asphalt pavement (RAP) is important for any asphalt business. It not only saves the planet by recycling, but it also saves your bank account. Astec has a variety of products that have changed how to use RAP. Let’s take a closer look at the options to incorporate recycle into the mix.
“The Double Barrel® has been our bread and butter dryer/mixer since 1988,” stated Greg Renegar, senior vice president engineering at Astec, Inc. It’s the mixer chosen over any other. The sequential mixing allows better temperature equalization throughout the mix and it features Astec V-flights for the veiling of material over a wide range of tonnages. The virgin aggregate temperature is measured to automatically adjust to the burner.
“If you want to recycle up to 50 percent, the Double Barrel® is the solution. If state DOT’s allow more than 50 percent RAP, Astec has alternative options,” said John Irvine, executive vice president of Astec, Inc.
Double Barrel® XHR
The Double Barrel® XHR is a high RAP drum mixer with an external mixer. This system uses V-flights and a drum VFD (variable frequency drive) to help facilitate producing many different types of mixes, while controlling the temperature. It cuts the added cost and the lost time of flight changes, because its wider veil increases its effectiveness by exposing more material to hot gases. The Double Barrel® XHR keeps operating costs down while making use of stockpiles of reclaimed asphalt pavement, running mix from 0 percent up to 65 percent RAP. It creates a high-quality mix with high RAP by employing two mixing technologies that have been around for a quarter of a century in the HMA (hot-mix asphalt) industry by using an outer chamber on the drum and an external mixer. The stainless steel drum and combustion flighting withstand the higher temperatures associated with running high RAP.
Astec offers innovative solutions for calculating and using recycle in asphalt mixes.
Double Barrel® XHR with RAP Pre-Dryer
Astec is developing new technologies that will improve the amount of RAP that can be used in mixes. The latest project is the external RAP heat recovery pre-dryer. It uses the existing gas stream coming off the Double Barrel® drum and runs it through another dryer either adjacent to or on top of the Double Barrel®. The RAP is preheated before it enters the mixing chamber of the Double Barrel®.
Irvine continued: “We’ll run it through another dryer and use it to preheat the RAP before we drop the RAP into the main dryer. Our hope is that this new technology will help the Double Barrel® XHR be able to run up to 80 percent RAP.”
Benefits of RAP
The number one benefit of using RAP is cost. The aggregate itself hasn’t really aged. It has the same physical properties as it did the day it was originally crushed and used to make a road.
“The return on investment is high,” said Michael Varner, Astec chief engineer. “If you look at the evaluation of recycle, it adds anywhere from 34 to 44 cents per percent per mixed ton. That number comes from the value that is inherent in the materials that makes up RAP—the liquid that is in the RAP, the asphalt cement or the binder, and the rock.
Recycle is worth the material it’s replacing. Some areas have more asphalt pavement to be reclaimed than other areas. Using recycled aggregate saves money that would’ve been spent on virgin aggregate.”
There are many asphalt plants in the U.S. that are taking advantage of this new innovation; one such operation is P&S Paving in Daytona, Florida. P&S Paving’s facility has an Astec Double Barrel® XHR, operating since the first week of March 2015.
Tim Phillips, president of P&S Paving noted: “With Astec, we have the best available equipment in the industry. We have all the tools, so now it’s just up to us to make good mix.”
New Online Tool
Astec has a new tool that can help customers decide which equipment is best for them. “It’s an online analysis spreadsheet.
Any contractor could visit the website, access the spreadsheet, and enter data such as the cost of aggregate; cost of the liquid asphalt (AC); the RAP crushing, screening, and trucking cost; the tons per year; and the percent RAP usages.
The tool will calculate a payback analysis of purchasing a new plant (Double Barrel®, Double Barrel® XHR, Double Barrel® XHR with RAP pre-dryer),” said Irvine.
The tool is essentially a RAP calculator that helps customers determine how high a percentage of RAP they can use and whether or not it would be cost-effective in the long run. This is based on the information entered into the spreadsheet. Check out the RAP calculator: astecinc.com/rap-roi
Varner uses the following analogy when explaining the use of recycle to customers: “Running 30 percent RAP is like balancing an elephant on one of those little cones at the circus. When running 45 to 50 percent RAP, you’ve now put your elephant on a post. When you go beyond that running 60 percent, 65 percent, and 70 percent, you’re really getting to the point where your elephant becomes precariously balanced. The equipment must incorporate technologies and configurations to keep the elephant as stable as possible.”
P&S Paving chose the Astec Double Barrel® XHR, a high RAP Double Barrel® drum with an external mixer, for its new facility.
P&S Paving’s Double Barrel® XHR keeps operating costs down while making use of RAP stockpiles.
P&S Paving’s asphalt plant has a 10 ft x 14 ft (3.05 m x 4.27 m) five-compartment cold feed system.
P&S Paving’s asphalt plant has a 85,242 CFM Pulse Jet baghouse.