The Virginia Department of Transportation (VDOT), like other state DOTs, strives to hold the line on highway maintenance costs, especially for petroleum-based asphalt and binders. VDOT uses asphalt concrete to pave most of the roads in Virginia.
VDOT's research division, the Virginia Transportation Research Council (VTRC), is investigating several green technologies to help VDOT save money — and reduce waste — on this evermore costly material. One VTRC project analyzed a field installation using the asphalt from roofing shingles in the pavement binder, to good results.
A 4.1-mile, two-lane section of Route 671 in southeastern Virginia was paved using a surface mix containing 5-percent shingle waste as well as another surface mix with 10-percent recycled asphalt pavement for comparison. The Research Council conducted density tests on the pavement and various laboratory tests — permeability, fatigue, tensile strength ratio, rut, and binder recoveries — on samples collected during construction.
Both the field and lab test results indicated that the behavior and performance of the two mixes should be similar. In fact, the shingle mix is still performing well on the road after two years of service.
In the 1990s, state legislation directed VDOT to form a "Recycled Materials in Highway Construction Advisory Committee" to recommend how VDOT might use various recycled materials — glass, tires, plastics, aggregate fines, bituminous concrete, among others — in highway construction.
The committee also recommended research into the use of recycled roofing material. As a result, VDOT developed a draft specification for its trial use in asphalt concrete in 1999. The specification allowed either tear-offs — roofing removed from buildings — or manufacturing waste.
Manufactured shingle waste tends to be more consistent in material characteristics than tear-offs and contains no harmful materials such as asbestos. VDOT wanted to gain experience and verify that the process would produce mixes equal to or better than those without shingles. VDOT also hoped to use the draft specification to place trial sections upon request from contractors before providing blanket approval for a specific source and process.
Although there had been inquiries before 2006, no contractor had asked to place asphalt concrete containing roofing material. In 2006, a North Carolina contractor did request VDOT's approval to use asphalt concrete containing manufactured shingle waste. Although the source of the shingle waste was in North Carolina, there was a potential advantage in decreasing the cost of the asphalt concrete in VDOT's Hampton Roads District in southeast Virginia near the contractor's plant in nearby Gaston, NC.
With the considerable rise in the cost of asphalt binder and the fact that shingles contain an appreciable amount of asphalt binder, the future savings in the cost of such a mix binder could be substantial. It is likely that approximately 50,000 tons of hot-mix plant mix containing waste shingles could be supplied to VDOT's Hampton Roads District per year from this contractor. As much as $2.69 could be saved for every ton of asphalt that uses the waste shingles.
The study recommended that VDOT's Materials Division prepare a permanent special provision to allow the use of manufactured shingle waste in asphalt, which has been completed. Implementation of this special provision has the potential to save $134,500 per year in the Hampton Roads District alone.
When the report for this project was written in January 2008, binder was costing approximately $340 per liquid ton.
Following the success of this project, VDOT's Asphalt Research Advisory Committee has also recommended that the Research Council study the use of tear-off shingles both in the lab and in the field. The study is expected to begin later this year.
The Research Council report, Use of Manufactured Waste Shingles in a Hot-Mix Asphalt Field Project in Virginia, by G.W. (Bill) Maupin Jr., VTRC 08-R11, is available at http://vtrc.virginiadot.org/PUBDetails.aspx?Id=296357.