By: Prithvi "Ken" Kandhal, P.E.
Roofing shingles reduce cost of HMA It is estimated that 11 million tons
of waste roofing material are generated annually in the U.S. This is more
than four times the 2.5 million tons of scrap tires generated each year.
However, during the last five years, considerable time and resources have
been devoted to researching the use of scrap-tire rubber in hot mix asphalt
(HMA) pavements, whereas almost negligible research effort has been directed
at the use of waste-roofing material (shingles) in HMA.
Unlike the use of crumb rubber from scrap tires, the use of roofing shingles
is both technically feasible and has the potential of providing significant
economic benefits by reducing overall cost of HMA mixtures . Such a use also
eliminates the environmental concerns and costs associated with the disposal
of roofing shingles in landfills.
Of the estimated 11 million tons of waste-roofing material, about 10 million
tons come from roofing replacements or "tear-offs". The remaining
million tons is generated as a waste (seconds or factory scrap) from new
roofing-shingle manufacturing. Most of the waste-roofing material is currently
disposed of in landfills at a cost ranging from $18p;$45 per ton.
Roofing shingles contain a substantial amount of asphalt cement binder (about
30% in organic shingles and 20% in fiberglass shingles). Therefore, the
use of roofing shingles in HMA will reduce the amount of required virgin
asphalt binder. Moreover, asphalt roofing shingles contain high grade mineral
filler and cellulose fiber, which are very likely to enhance the engineering
properties of the HMA.
Field trails in Florida, Indiana and Minnesota, states which generally use
5% roofing shingles in HMA, have shown encouraging pavement-performance
results. The commercially available, shingle-shredding equipment, has been
developed and modified based on the experience gained in the field trails.
It has been estimated that by introducing 5% organic shingles, the HMA cost
can be reduced by $2.79 per ton, which is economically very attractive.
There is a need for a concerted research effort (similar to the efforts
devoted to scrap-tire rubber) by the highway agencies and the industry for
utilizing waste-roofing shingles in HMA. Mix design procedures should be
developed for HMA containing both "tear-offs" and scrap waste
from the manufacturing process. Construction of field demonstration projects
also should be encouraged by state highway agencies. The use of roofing
shingles in HMA is very likely to provide an excellent opportunity for reducing
the overall costs of HMA and enhancing its engineering properties, while
eliminating a major environmental problem.
About The Author: Kandhal is the Associate Director at the National Center for Asphalt Technology at Auburn University. You may write him in care of the editor.
