The use of recycled materials is at an all-time high; largely because of the savings in materials costs available to asphalt mix producers. Given the successful performance of most of these mixtures, the use of recycled materials will likely continue to grow.
In order for these hybrid mixtures to perform well, there are some important points to recognize. Mike Anderson, AI’s Director of Research and Laboratory Services, and I have written an article on using RAP (recycled or reclaimed asphalt pavement) for the summer issue of “Asphalt” magazine. That article summarizes some of the key points that need to be understood in order to best include RAP in asphalt mixes.
Asphalt roofing shingles are another recycled material that is becoming more attractive to asphalt mix producers. Approximately 11 million tons of shingle waste is generated in the U.S. each year. 10 million tons of this total are old (post-consumer) or tear-off shingles. New (or manufacturers’ waste) shingle pieces make up another one million tons.
As with RAP, there are some key points to recognize in order to get good performance when using RAS (recycled asphalt shingles). One of the most important considerations with RAS is to recognize the significant difference between old and new shingles. Because of these differences, some agencies have restricted shingle recycling in asphalt to manufacturers? waste.
Old, tear-off shingles generally have more and harder asphalt than new shingle material. Old shingles were typically made with a higher asphalt content than modern shingles and have lost some of the aggregate granules during their service life, resulting in the asphalt making up a higher percentage of the total weight.
Old shingles, typically made with a felt base, have an asphalt content of 30 to 35 percent; new shingles, made with a fiberglass mat base, more typically contain about 20 percent asphalt.
Old shingles have undergone additional oxidation (hardening) of the asphalt while in service. And modern shingles may contain some polymer-modified asphalt, which is considerably different than the asphalt in old shingles.
Another difference is the cleanliness of, or amount of contamination within the shingles. Old shingles tend to have pieces of wood, nails and other deleterious materials, while manufacturers? waste shingles should be clean.
Another potential concern with tear-off shingles is the possibility of asbestos fibers within the shingle. Older shingles, especially those removed from multiple layers of in-place shingles, could contain asbestos. Encountering asbestos in residential shingles is an extremely rare problem; it is slightly more likely to be found in old commercial roofing waste, mastic, caulking, etc.
With about 15 years of experience using reclaimed shingles, most agencies report satisfactory performance from RAS mixtures. By understanding some of the unique properties of these materials, this positive performance can continue.