290 likes | 454 Views
RAS Best Practices. PAPA 54th Annual Paving Conference Hershey, PA January, 30th 2014. RAS Best Practices. What is RAS?. RAS Best Practices. Recycled Asphalt Shingles. Types. 2 types of roofing shingle scraps:
E N D
RAS Best Practices PAPA 54th Annual Paving Conference Hershey, PA January, 30th 2014
RAS Best Practices What is RAS?
RAS Best Practices Recycled Asphalt Shingles
Types • 2 types of roofing shingle scraps: • Tear-offs generated during the demolition or replacement of existing roofs • Manufactured waste generated when new asphalt shingles are trimmed during production to the required physical dimensions or from "out-of-spec" shingles
Composition Shingles typically contain: • Asphalt binder • Tear-offs contain 20 – 40% binder • Manufacturer waste 18 – 22% binder • 40 to 60% hard rock granules and fillers • 1 to 12 % fiber, felt, and miscellaneous materials
Industry Guidance NAPA IS 136: Guidelines for the Use of Reclaimed Asphalt Shingles in Asphalt Pavements
Experience • Incorporating RAS into HMA began more than 30 years ago • Pennsy Supply began using shingles in PA in 2002 • PennDOT currently only allows Manufactured RAS, but may be considering allowing use of Tear-Offs
Environmental Concerns • Similar concerns as for aggregate crushing, RAP processing/crushing & HMA production • Asbestos screening (if using tear-offs) • Must comply with local agency requirements, which vary from state to state
Environmental Benefits • HMA mixtures produced with shingles are 100% recyclable • Saves natural resources • Saves landfill space
Processing Shingles • Various types of industrial grinders can be used to grind the Shingles into a usable product • Most use shredding approach • Water is used during processing for dust suppression and to aid in shredding, but must be controlled
Processing Shingles • Separate out the non-shingle debris before incorporating into HMA • Keep all non-shingle debris separated
Processing Shingles • Ensure proper sizing of the ground Shingle particles • Finer is better • Oversized Shingle particles impact: • Contribution to Pbe • Mat texture
Processing Shingles • Test RAS for gradation & AC Content frequently as they are being shredded • Keep RAS of different AC contents in separate stockpiles
Processing Shingles Pre-Processing Post-Processing
Processing Shingles • In some cases RAS is blended with a carrier aggregate: • Used to keep Shingles from conglomerating & allows for more efficient flow through cold feed bin • RAP, 3/8” Stone, washed screenings, Natural Sand can be used
Storage • Store RAS in covered environment to control moisture • Shingles left exposed to rain can have very high moisture contents (12%+) • RAS holds more moisture than RAP
Plant • Not always a best practice to keep the shingles bin full • Best practice to empty the shingles bin when production complete or production is stopped for extended period Photo courtesy of Astec Industries
Plant • Ensure the RAS feed system is calibrated and maintained Photo courtesy of Astec Industries
Plant • Load cells or weigh belts measure the amount of RAS as it is metered into plant Photo courtesy of Gencor Industries
Plant • Watch for build-up at the RAP collar, especially for plants with smaller throats
Plant • Consider covering conveyors and transfer points
Plant • Test moisture content of RAS often while incorporating into mix – even more frequently if RAS stockpiles are not covered
Plant • RAS has been used successfully in batch and drum facilities • May need to increase dry & wet mix time in batch plants
Temperatures Higher plant production temperatures may be needed to ensure all moisture is removed from RAS & to maximize blending of RAS binder with virgin binder
Temperatures Higher plant production temperatures may be needed to ensure all moisture is removed from RAS & to maximize blending of RAS binder with virgin binder
Field • RAS mixtures can behave differently than virgin mixtures or RAP mixtures, which doesn’t necessarily make them bad: • RAS mixtures tend to be more sensitive to fluctuations in production temperatures • RAS mixtures are typically stiffer so may require additional effort to compact • RAS mixtures may make hand-work more difficult , so think through paving sequence before you begin paving
Summary • Shingles require processing • Need consistent stockpiles of RAS • Should cover stockpiles of RAS • Test gradation & moisture content of RAS often • RAS feed must be calibrated & controlled • Higher production temperatures may be needed • Be prepared to manage deltas in mix characteristics when placing RAS mixtures