Shingles - a valuable paving resource

With the ?green? movement starting to build momentum in the asphalt industry as an environmentally sustainable approach to serving the road paving needs of this country, a Minnesota asphalt producer/contractor continues to promote that concept by incorporating waste roofing shingles into the hot mix it produces and places.

Bituminous Roadways Inc., based in Inver Grove Heights, MN, recently completed a 2.7-mile stretch of Trunk Highway 149 in Eagan, MN, using a mix design containing a low percentage of roofing shingles.

The project consisted of reconstructing an existing two-lane road into a four-lane divided highway with upgraded controlled intersections and an additional controlled intersection.

The City of Eagan, in partnership with the Minnesota Department of Transportation, wanted to improve traffic flow and increase safety along this project. The original project scope included approximately 105,000 cubic yards of common excavation, 63,000 tons of Class 6 aggregate base and 70,000 tons of bituminous pavement. Park Construction Co. of Hampton, MN served as the general contractor of the $9.1-million project, with Bituminous Roadways serving as the asphalt paving subcontractor. Bituminous? portion of the project represented $3.4 million of the contract.

Some of the more notable benefits of the shingle mix design used on the 149 project included:

• BRI achieved an average International Roughness Index of 34.18 inches per mile.

For MnDOT new construction projects consisting of three or more lifts of HMA, full bonus incentives are awarded when the IRI does not exceed 30 inches per mile. BRI received a ride bonus of $21,000 on this project.

• The project owner saved an additional $100,000 by allowing shingles to be used in the mix versus only allowing recycled asphalt pavement (RAP). Using five percent shingle content generated $1.43 per ton savings.
• BRI also received a density incentive of approximately $50,000 determined by core samples pulled from the project.
• The composition of the waste shingles used on the project consisted of approximately 20 percent asphalt, 70 percent granular material (mineral filler and high quality aggregate), and 10 percent backing (cellulose or fiberglass).

Project challenge

Since Hwy. 149 serves as a major connection between State Hwy. 55 and State Hwy. 3, providing access to several major businesses, the road needed to remain open to traffic during construction.

?Since the project called for converting and existing two-lane road into a divided four-lane highway with controlled intersections, it was basically a total full-depth reconstruction requiring reclamation of the surface asphalt and removal of some of the concrete roadway,? notes Dusty Ordorff, quality control and materials manager for Bituminous Roadways.

?Our portion of the project (asphalt placement) required us to place four 2-inch lifts of Traffic Level 4 Superpave (four inches of non-wearing base and four inches of wearing course),? he continues. ?The mix design is what MnDOT specifies for high-volume roads (over three million ESALs).?

The non-wearing course consisted of a PG 58-28 binder with 12.5mm nominal aggregate size and 3 percent air void. The wearing course consisted of a polymer modified PG 64-34 binder, 12.5mm nominal aggregate size and 4 percent air void when compacted.

?On the non-wearing mix design we were allowed to use 15 percent reclaimed asphalt pavement (RAP) content and 5 percent recycled roofing shingles,? Ordorff notes. ?On the wearing course mix design we had to limit the RAP content to 5 percent, but we were still allowed to use 5 percent shingle content ground to 5/16-inch minus and ground just-in-time to avoid re-agglomeration.

?A year ago, MnDOT changed the specs for mix designs containing recycled shingles, stating that 70 percent of the asphalt cement binder in a mix had to be new,? he continues. ?That restricts the amount of RAP in shingle mixes.?