?We now treat waste shingles the same as RAP,? notes Roger Olson, research engineer for MnDOT. ?If we award a project that allows the mix to contain 30 percent RAP content, the contractor can place a mix that has 25 percent RAP and 5 percent waste shingles. As long as the performance characteristics meet our spec requirements, we consider shingles to be the same as RAP. I do think we?ll eventually develop similar specifications for using tear-offs (old shingles).?
For the Hwy 149 project, the equipment Bituminous? paving crew used to place the mix included a Weiler E650 windrow pickup machine, a Blaw Knox PF5510 paver equipped with a Smoothtrac sonic averaging ski and a Blaw Knox drag style ski, a Cat 634 84-inch vibratory breakdown roller, a Sakai SW 850 79-inch vibratory breakdown roller, a Sakai GW 759 vibratory pneumatic intermediate roller, and a Hypac 766 66-inch finish roller.
The paving crew used a Seaman nuclear gauge and a Transtech PQI non-nuclear gauge to monitor pavement density.
10 years of experience
Bituminous has been recycling waste shingles since 1996 and has produced over two million tons of HMA with shingles added since then, recycling over 100,000 tons of scrap shingles. A bulk of Bituminous? shingle supply comes from a local shingle manufacturer that generates 30,000 to 40,000 tons of rejected shingles annually.
?They (shingle manufacturer) were sending their product to another company that was stockpiling the waste shingles and the manufacturer wanted the material to be recycled, so they started sending their factory rejects to us 12 years ago,? Ordorff says. ?What we don?t use for our own production we give to an asphalt producer out of our market area.?
Bituminous Roadways operates three asphalt plants in the Twin Cities, producing over a half million tons of HMA annually.
Ninety percent of what the company produces is used to support its own paving crews.
As the company grew from a parking lot paving contractor to one that now paves city streets, county roads and state highways, Bituminous began to incorporate shingles into the mix it produced in the mid-1990s as a way to lower production costs and become more competitive in the market. The Minnesota Office of Environmental Assistance helped Bituminous to have the shingle content specified as part of the mix design it would supply road agency projects. The company processed 1,000 tons of waste shingle in 1996 and 27,000 tons in 2007.
?Until MnDOT changed the specification on shingle content about five years ago, we had to have approval from a project engineer in order to use shingles; and that was a major roadblock over the years in trying to increase usage,? Ordorff says. ?We did quite a few demo projects over the years, and Hennepin County has been a big supporter by executing some major test projects using a shingle mix.?
?We conducted our first test project using hot mix with shingles added in 2002 on a typical county road with medium traffic volume,? notes Steve Peterson, technical coordinator for Hennepin County?s road department. ?At the time we were interested in the cost savings (approximately $1 per ton) of buying mix with shingles to supply the projects we handle with our own paving crews. Since then we?ve purchased approximately 56,000 tons of asphalt mix that contains waste shingles and the projects have performed well. We award material contracts based on each individual project bid. We?ve been happy with the asphalt performance, we like the fact that it does save us some money, and we?re also happy that using shingles in hot mix does reduce the waste that?s sent to landfills.?
A recycling commitment
Ordorff admits it was not easy to convince project owners to allow a shingle mix design, since there was no historical experience to benchmark performance.
?MnDOT tweaked the specs a few years ago regarding shingle usage and now it?s treated like RAP,? Ordorff says. ?Shingles are a consistent product that contains valuable components used to produce HMA. Eighty-six percent of the mix we produce at our company now contains roof shingles. Pound per pound, a roof shingle is twice as valuable as RAP, and definitely saves money for us and our customers. I think you?re going to see more asphalt producers/contractors working to recycle shingles just as they do with RAP.