Plan Ahead: Where’s That Recycle Gonna Go?
When the most costly product in an asphalt mix is one that can be created on-site using recycled materials, the savvy producer will find many ways to work with it. Invest in the equipment you need to fractionate your millings, crush to size those chunks of recycled pavement, etc. Fractionating the product makes sense, but have you thought about where the product goes once you have it down to size?
Let’s start a discussion of metering and controlling ingredients such as recycled asphalt shingles (RAS) with tips for handling the material. Mitch Duncklee is a software engineer for Systems Equipment in Waukon, Iowa. He suggested producers could get more consistent feeding results if recycling operations stayed up to date with their practices.
“Pre-processing the shingles differently can make a large difference in how the RAS feeds,” Duncklee said. “While making mix, good feedback control in the blend computer can help smooth out the AC content, but any chance to prevent manic speed changes because of poor feeding should be looked into.”
He sees pre-processing as a positive step for future innovations. “Pre-processing and storage would go a long way to make RAS behave like a typical ingredient. It wouldn’t surprise me to see more buildings or shelters to store the more sensitive materials. A lot of money gets spent removing moisture and clumping in process. Why not eliminate it before it even gets to the bin?”
While a recycler will look at pre-processing as sorting the deleterious materials out of the shingle pile prior to grinding shingles to produce RAS, the asphalt plant owner can look at pre-processing at his site as declumping the RAS prior to feeding it into his drum. Preston McIntyre, a sales representative for Rotochopper, once explained that clumping or compacting of RAS usually occurs in one of two ways.
“When material is run over by a loader or similar piece of heavy equipment, it compacts,” McIntyre said. “Another clumping occurrence can happen if a pile of RAS sits for an extended period of time; it can conglomerate due to the heat of the sun and its own weight if the pile is quite high. The outer layer of the pile is typically the only area affected by the sun.”
McIntyre suggested if either the problem of agglomeration or clumping occurs, send the effected RAS through the grinder for a quick, second pass to bring the RAS back to usable form. He also reminded readers they can use simple additives to prevent clumping.
When stockpiling or feeding RAS, time, temperature and moisture can cause agglomeration of the particles into clumps that negatively influence quality control. While using sand in the RAS stockpile has the secondary benefit of shining some plant components by preventing RAS from sticking as it goes through production, it can have a negative influence on QC, depending on the cleanliness of the sand. Clean sand can be costly. Dirty sand can throw a good mix off kilter. Check with additive suppliers for solutions they have to this problem.
Along with fractionating RAP and declumping RAS, producers will want to prep stockpile areas when considering where the recycle material goes. Everyone knows by now to pave beneath stockpile areas. Put berms between stockpiles of differing materials or sizes. Put signs at the edge of stockpile locations to let truck drivers and loader operators know exactly what is in each bay. And then match up those signs to the cold feed bins nearer the plant.
Argo Industries, Inc., Brookfield, Wis., offers a bin designed specifically for RAS. “We use a vertical front wall and steeply sloped side and end walls along with a cleated belt to improve flow ability,” Paul Vandermolen of Argo said. “What we have found with our users is that when this material is being processed in bins with flatter slope angles, the material tends to pack.”
To get material ready, try these steps that Preston McIntyre suggested for basic grinding:
Step 1. Single-pass grinding through a small screen hole size
Step 2. Double-pass grinding through a larger screen, and then a smaller screen
Step 3. Grind, screen and then regrind the overs
In the end, the purpose of taking so much time with your recycle material is to get a bonus-worthy mix design. Give quality control your full attention from the moment millings and other recycle material reaches your facility until the final product is in the mix and you’ll know where your recycled product is headed: it’s headed to the bank.
Take a Class with ARTBA
The American Road & Transportation Builders Association Foundation will host two professional development courses this March. The Project Management Academy (PMA) and P6® Scheduling Academy are designed to help both new and experienced transportation construction industry professionals better manage their firms’ projects.
- PMA = March 9 through 11; $1,999 for ARTBA members ($2,499 for non-members)
- P6 Scheduling Academy = March 11 through 13; $1,700 for ARTBA members ($1,999 for non-members)
The highly-acclaimed PMA is built around an acknowledged adult learning model of instruction supported by peer-to-peer knowledge sharing. It offers both tools and critical thinking skills in these core subjects: Planning & Scheduling; Industry Ethics; Client Relations; Construction Documentation; Management/Leadership & Resource Management; and the Economics of Safety. The P6® Scheduling Academy will provide in-depth instruction on Primavera Project Planner (P6®) software and other “tricks of the trade” to help efficiently track key project aspects, such as people, materials, operational benchmarks and payment schedules. This unique program uses hands-on training designed specifically to help industry professionals adapt the P6® software to their own needs. Dr. Newitt will also guide students through the complex principles of Critical Path Method scheduling, which can help with timing and resource allocation during the delivery of complex transportation construction projects.
Both academies provide attendees an opportunity to earn up to 32 Professional Development Hours. Visit www.artbatdf.org to register, or contact ARTBA’s Kashae Williams at (202) 289-4434, ext. 109.