I. RESEARCH PROBLEM STATEMENT
The use of Recycled Asphalt Shingles (RAS) in Hot Mix Asphalt (HMA) and Warm Mix Asphalt (WMA) mixtures has increased dramatically over the last three years (approximately 700,00 tons in 2009 and 1.2 million tons in 2010). Over 15 states currently allow the use of RAS in their HMA and WMA paving materials. This increased use of both manufactured (manufactured shingle scrap byproduct) and post-consumer (tear-off shingles from re-roofing operations) is largely a result of paving industry economics and societies desire to recycle and conserve our natural materials. Since the introduction of WMA, additional initiatives to reduce energy consumption, reduce emissions and reduce green house gases, has also occurred.
The use of RAS has largely been advanced by the materials supplier and contracting industry. States have accepted the use of RAS in HMA and WMA with limited engineering and performance data. Typically quantities of RAS used in paving mixtures range from 3 to 5 percent by weight of HMA or WMA mixture. Since RAS has a relatively high asphalt binder content (20 to 30 plus percent by weight of the shingle), asphalt binder substitution ranges from 10 to 30 percent in the HMA and WMA. Many currently produced RAS mixtures contain RAP. These mixtures are produced with hot mix and warm mix processes.
RAS binders are very stiff with PG high temperature grades in the range of 110 to 140 C and low temperature grades in the range of 0 to 15 C. Recycled mixtures with RAS and with RAS/RAP may be prone to fatigue cracking, reflection cracking, low temperature cracking, aging and raveling which will reduce their service life. In addition, the use of high RAS and RAP mixtures may cause placement (workability) and compaction problems during construction.
Since RAS binders have very high softening points, their use in WMA mixtures may result in incomplete blending of the RAS asphalt binder and the virgin asphalt binder. Engineering and performance data needs to be obtained on a nation-wide basis to develop specifications for the use of RAS and RAS/RAP combinations.
II. LITERATURE REVIEW
A FHWA state pooled fund project is currently in progress at Iowa State University. Some states including Texas have HP&R research projects underway. Some technical papers have been presented at TRB in the past three years. These studies are limited geographically and in scope.
NCHRP is currently or has recently sponsored several projects on the use of RAP and WMA. None of these studies included or will include the use of RAP in the mixtures under study. A specific project addressing the use of RAS is warranted.
III. RESEARCH OBJECTIVE
The objective of the research project is to define the engineering properties of HMA and WMA mixtures containing RAS and RAS/RAP combinations. The following subtasks are proposed:
1. Characterize the asphalt binders extracted and recovered from RAS and RAP as well as HMA or WMA mixtures containing virgin materials and RAP/RAS combinations (representing 100 percent blending) and compare to predicted blending, based on measured mixture properties and predictive equations such as the Hirch Model.
2. Characterize the engineering properties of HMA and WMA mixtures containing RAS and RAS/RAP combinations
3. Predict performance of HMA and WMA mixtures containing RAS and RAS/RAP combinations
4. Establish field test sections to study the short term performance of HMA and WMA mixtures containing RAS and RAS/RAP combinations
5. Evaluate the short term performance of HMA and WMA mixtures containing RAS and RAS/RAP combinations
6. Update and propose revisions as necessary to AASHT provisional standards MP 15-09, “Use of Reclaimed asphalt Shingles as an Additive in Hot Mix Asphalt” and PP 53-09, “Design Considerations When Using Reclaimed Asphalt Shingles (RAS) in New Hot Mix Asphalt (HMA)”. The revisions should include the use of RAS and RAS/RAP combinations in HMA and WMA (include characterization of the asphalt binders, characterization of mixtures and mixture design methods)
7. Develop training/workshop materials including recommended practices based on the results of this project and deliver one workshop
It is anticipated that the majority of the engineering properties of the mixtures will be performed on plant mixed-lab compacted samples. The field test sections will be documented such that a long term performance study can be conducted using these sections on another research project.
IV. ESTIMATE OF THE PROBLEM FUNDING AND RESEARCH PERIOD
Research Period-40 months (Interim reports will be published during this period)
V. URGENCY AND PAYOFF POTENTIAL
Over 1.2 million tons of RAS were used in HMA and WMA mixtures in 2010. This quantity will increase in 2011 and beyond. Methods need to be developed to insure that the performance of HMA and WMA containing RAS and RAS/RAP combinations perform equal to or better than conventional HMA.
The use of RAS, RAP and WMA reduces the consumption of energy, reduces emissions, reduces green house gases and conserves or natural resources as well as reduces the cost of HMA. The proper design and utilization of these material combinations needs attention in the immediate future.