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191 Best Practices for Processing Recycled Asphalt Shingles Introduction As a result of increasing prices for construction of asphalt pavements, contractors as well as state DOTs continue to look for ways to reduce asphalt production costs. One method to reduce costs that has shown promise and that has been adopted by many state DOTs and contractors is to use reclaimed asphalt shingles (RAS) as a component of the asphalt mix- ture. RAS contains a high amount of asphalt binder and can be used as partial replacement for the costly virgin asphalt binder. RAS has been used for many years in asphalt pavements, but it began to gain popularity during the early 2000s because of the continuing cost increases of asphalt binder. Improvements made in shingle processing and stockpiling techniques also helped to facilitate the use of RAS in asphalt mixtures. The use of RAS has increased much during recent years, and this use is expected to continue to increase in the future (Hansen and Copeland 2015). There are two general sources of RAS available for use in asphalt mixtures: manufacturersâ waste (MW) and post- consumer (PC) waste (often referred to as âtear offsâ). It is estimated that there are approximately 7 to 10 million tons of PC waste and 750,000 to 1 million tons of MW generated per year that has to be disposed into landfills if the RAS cannot be recycled (National Association of Home Builders 1999). MW is created during the production of asphalt shingles from material rejected for various reasons that typically do not affect the RAS components. MW has not been exposed to the sun and elements; therefore, the asphalt binder is much less stiff than the asphalt binder contained in PC waste. Expo- sure to sun and the elements will oxidize the asphalt binder, resulting in a significant increase in stiffness. MW does not contain the deleterious materialsâsuch as wood, metal par- ticles, and nailsâfound in PC waste. Because of deleterious materials, PC waste often requires a lot of cleanup to remove most of these deleterious materials before the processed RAS can be used as a component in asphalt mixtures. Table D-1 shows the percentage of materials that might be recovered from PCâRAS. Working with roofing contractors to empha- size the need for cleaner PC waste can result in much of these contaminating materials being removed prior to delivery to the asphalt contractor. For older shingles, the asphalt content in RAS can vary from just under 20% to over 35%, as shown in Table D-2 (National Association of Home Builders 1999). This high asphalt content has been reported to be typical in RAS; however, most test laboratories have reported measured asphalt content on the low end of this range. Using up to 5% of PCâRAS in an asphalt mixture can reduce the need for virgin asphalt binder by approximately 1% or more simply because of the addition of the RAS, which has high asphalt content. The asphalt binder content in newer shingles has been shown to generally range between 15% and 20%. Since the shingles available in current MW are new, the asphalt content in these shingles is typically in the range of 15% to 20%. The primary reason that recently produced asphalt shingles have less asphalt binder is because of the manufacturers taking steps to reduce the asphalt content of the shingles, since the cost of the asphalt binder is a signifi- cant part of the cost of the shingles. Modern shingles tend to use fiberglass mats, while in the past more cellulose mats were used. Cellulose shingles require more asphalt cement content than fiberglass shingles. Also, with the price of asphalt binder increasing, roofing manufacturers have taken steps to reduce the asphalt content in their shingles. Some of the older asphalt shingles that were produced in the 1970s and earlier often contained small amounts of asbestos. While the amount of asbestos was small, care must be taken to ensure compliance with federal laws when dealing with these old shingles. Since the late 1970s, asbestos has not been used in the production of shingles. The RAS contained in most PC waste was manufactured since the late 1970s and, hence, also does not contain asbestos. However, it is good practice to have the asphalt shingles to be used on a project tested for asbestos. A P P E N D I X D
192 Now that RAS is permitted by most state DOTs and used by many contractors in asphalt production, more guidance is needed for its use. This document provides best practices for processing and stockpiling the recycled asphalt shingles. Using these best practices will ensure better handling char- acteristics, improved mixing with other asphalt components, and better performance of the asphalt mixture. Regulations Those using RAS must make sure to follow best practices to ensure that the RAS can be safely handled prior to mixing with the mixture components and throughout the mixing and paving process. All local, state, and federal regulations must be followed when using RAS in asphalt mixtures. Some potential regulations to consider include (National Associa- tion of Home Builders 1999): â¢ Local zoning, â¢ Construction/operation permits, â¢ Solid waste/recycling permits, â¢ Occupational Safety and Health Administration requirements, â¢ Asbestos management regulations and other asbestos requirements, â¢ Stormwater requirements, and â¢ Air emission and dust control. Collection of RAS RAS can be collected from roofing contractors that remove old shingles from existing roofs (PC) or from MW during asphalt shingle production. Asphalt shingles from household roofs are the most common source of PC shingle waste. Tech- nology is not available to use built-up roofing as a source of RAS to be recycled in asphalt mixtures and, as a result, these materials should not be mixed with roofing from households. The quantity of PC shingles is far greater than the quantity of MW, as roughly 10 million tons are produced from PC waste and roughly 1 million tons from MW per year (Northeast Recycling Council 2012). Hence, states that allow the use of PC waste typically see a much larger quantity of this product being used compared to MW. PCâRAS has typically been exposed to sunlight and the envi- ronment for 20 to 40 years and has experienced a high degree of oxidation, making the asphalt binder in these shingles much stiffer than the asphalt binder contained in MW. As previously mentioned, PC shingles also contain significant amounts of deleterious material that must be removed before being fully processed for use in asphalt mixtures. Another potential issue with PCâRAS is the possibility of asbestos in the shingles. Asbestos was a component used in shingle production by some manufacturers until the mid to late 1970s, so it is possible that PC shingles may have a small amount of asbestos (Construc- tion and Demolition Recycling Association 2004â2018). Most shingles produced in the U.S. during this time did not use asbestos, and those shingles that did contain asbestos typically used less than 1%. It is not known what amount of foreign- produced shingles contained asbestos or the percentage of asbestos in these shingles. In 1993, the U.S. Environmental Pro- tection Agency developed the Method for the Determination of Asbestos in Bulk Building Materials (EPA/600/R-93/116), a test method using transmission electron microscopy to deter- mine the presence and amount of asbestos in a sample of RAS. Very few test results have shown any measurable amount of asbestos, but there have been a few tests that have shown some small amount of asbestos. For safety of employees and for liability reasons, it is recommended that some testing be performed on PCâRAS to ensure that there is no significant amount of asbestos in the materials. RAS from MW has not been exposed to the sunlight and climate. Therefore, the asphalt binder from these shingles is less stiff than the asphalt binder from PCâRAS. When using MW, there is no deleterious material that has to be removed. Asbestos is no longer used in asphalt shingles, so this is another issue that does not have to be addressed when using MW. It is easier to use MW in asphalt mixturesâif given a choiceâbut, as men- tioned earlier, the amount of PC waste is about 10 times as much as MW. Therefore, PC waste is much more widely used than MW, and steps have to be taken to process these materials so that they can be satisfactorily used in asphalt mixtures. These two sources of shingles act much differently when mixed with other components in an asphalt mixture. Hence, MW and PC waste should be maintained in separate stockpiles for best control of mixture quality. If both of these sources of Material Percent by Weight Tear-off waste shingles 85â90 Metal flashing/detailing 5â10 Wood sheathing <5 Tar paper <5 Paper packaging <1 Nails <1 Source: National Association of Home Builders,1999. Table D-1. Components of shingles removed from roofs. Material Percent by Weight Filler 8â40 Mineral granules 20â38 Asphalt cement 19â36 Felt backing 2â15 Source: National Association of Home Builders,1999. Table D-2. Typical asphalt shingle composition from PC waste.
193 RAS are used in the same mixture, their proportions should be maintained constant since the asphalt binders in these two products are much different and this can significantly affect the mixture properties. It is not recommended to interchange PC waste with MW during construction of a project. Inter- changing these materials can cause significant construction and performance problems. Collection Point for PCâRAS General The materials for MWâRAS are normally picked up by the paving contractor at the point of production. The asphalt contractor should obtain a material safety data sheet from the shingle manufacturer that describes the components of the shingles and any safety issues. These materials should gener- ally have no contamination and no asbestos, but they have to be processed by grinding and screening before being used in asphalt mixtures. The roofing contractor collects PCâRAS from local resi- dences that are being re-roofed. In the past these materials were discarded in landfills and in some cases are still being placed in landfills. The roofing contractor will welcome a reduction in cost to discard these materials at a collection point set up by an asphalt contractor. In most locations, contractors could initially charge the roofing contractor for accepting these materials, since this would still save the roofing contractor money compared to paying the landfill to allow these materi- als to be wasted. However, as more and more contractors have begun to use RAS, paving contractors often have to pay the roofing contractor to discard these materials at a point desig- nated by the paving contractor. The paving contractor needs to designate a drop-off point and negotiate a price for accept- ing these materials. A roofing contractor is generally willing to pay an asphalt contractor to allow disposal of the RAS at a designated location if there is not a lot of competition for these shingles. If the roofing contractor cannot get rid of these materials through someone who will recycle the shingles, the contractor most likely will have to pay to dump the material in a landfill. In many locations, competition between asphalt contractors for shingles has increased significantly, and as a result the paving contractor often has to pay for RAS to be dropped off at a collection point. Inspection of Deliveries Deliveries should be inspected to ensure that there is not too much contamination in the shingles. This contamination must be removed before processing. Having a fairly clean load of shingles will result in less work by the contractor and will ultimately result in a final product with less contaminants. Also, asphalt contractors can make note of roofing contrac- tors that deliver loads with higher amounts of contaminat- ing material and renegotiate their contract for future work. If a price for each load has been negotiated, it is important to keep track of the number of loads and either weigh these loads or ensure that each truck is fully loaded. Minimizing Deleterious Materials The RAS should be placed on a paved surface when pos- sible to help prevent contamination from underlying materials and to make it easier to handle the RAS. If a paved surface is not used, then care must be taken to ensure that underlying materials do not mix with the RAS during handling. Be sure to require that no hazardous material be included in the PC shingles; otherwise, this will create a significant problem for the paving contractor. RAS should not come from commercial properties where flat roofs are used, as components may be different and there is no guidance for using materials collected from flat roofs. It is much easier for the roofing contractor to clean up the PCâRAS as the material is being collected and loaded into a truck. Figure D-1 shows typical PCâRAS material that has not been cleaned of deleterious material. Much of the deleterious material can be easily removed at this point before the shingles are processed in the grinding equipment. After grinding, it is more difficult to remove the remaining deleterious material, since the particles will be much smaller and more difficult to identify and remove. Also, some deleterious material, if not removed, may damage the grinding equipment. An asphalt contractor can receive a much cleaner load of RAS by nego- tiating the price for the RAS with the roofing contractor. The price for accepting the RAS should be based on the material being cleaned of most of the debris before being delivered to Source: Wojahn 2014. Figure D-1. Asphalt roofing shingles with significant contamination.
194 the paving contractor. The effort to clean the material may cost the paving contractor a little more, but it is typically worth it to have the RAS partially cleaned when it is delivered to the paving contractor. Some paving contractors provide training programs for roofers to learn how to clean up the shingles before drop- ping off at the collection site. It is much easier for the roofing contractor to clean the RAS during removal from the home sites than for the paving contractor to clean it after it has been received. However, regardless of how well the roofing contractor cleans the stockpile, some additional removal of deleterious material will be required before the material can be used in asphalt mixtures. For example, there will certainly be a lot of nails, as well as other materials, in the RAS after the roofing contractor cleans the material, and these must be removed by magnets during the processing of the RAS. Sorting of RAS It is important to keep materials that are highly different in separate stockpiles. For example, PC waste should be handled separately from MW. The PC waste will have contamination and significant oxidation of the asphalt binder, while the MW will have very little or no contamination and very little oxi- dation of the binder. These materials should be stockpiled separately and should not be used interchangeably during production. It is not typically recommended, but both types of RAS can be used in a mix together as long as they are used in a constant proportion to maintain uniform mix proper- ties and a uniform surface during placement. In most cases, trying to use two different RAS materials will create so many issues with feeding two sources of RAS at very low percent- ages that it is not worth the effort to use more than one source of RAS at a time. Removal of Contaminants from PCâRAS Contaminants Removed by Roofer Roofing contractors can remove much of the contami- nants when the shingles are being removed from existing structures. At this time, one can place the shingles into one container and the deleterious materials into another con- tainer. Once the RAS has been processed through the grinder, it becomes more difficult for the paving contractor to remove the deleterious materials. Hence, it is recommended to clean as much of the material as feasible before any processing by the paving contractor. Contaminants Removed by Paving Contractor Once the RAS is provided to the asphalt paving contrac- tor, most of the remaining deleterious material will have to be removed. The best time to remove the largest deleterious materials is when materials are being unloaded, moved, or loaded to be processed (Figure D-2). When the material is being moved around, larger contaminants will be exposed and can be removed at that time. If not removed, contaminants may damage the grinder. There are typically many nails and other small pieces of metal in RAS. Much of these metallic particles can be removed with magnets that are attached over conveyor belts. This pro- cess can remove the metal particles as they are moved along the conveyor belt below the magnets. While this process will not remove organic materials, it does a good job of remov- ing most of the metallic particles. The best place to remove the metallic materials with a magnet is after grinding, as the particles are smaller and it is easier for the magnet to pull the metal particles from the RAS. The magnets and metal remov- ing operation will need to be inspected regularly to ensure that metal particles continue to be removed. Safety One should always use safe practices when working around RAS handling and stockpiles, especially when removing del- eterious materials. Removal of deleterious material is primar- ily done by hand and requires working around stockpiles of RAS, as well as around equipment such as loaders and mov- ing belts. Contractors should consider requiring workers to wear long pants, long-sleeve shirts, hard hats, safety glasses, gloves, safety vests, and steel-toe shoes. In some cases a respi- rator may be required because of dust in the mixture. Workers working near or on a stockpile must be careful, since a fall on the highly abrasive material can cause injuries. Some workers have been observed standing on stockpiles while front end loaders work around the stockpile. This is a very unsafe prac- tice and should not be done. Source: Zhou et al. 2012. Figure D-2. PC stockpile and clean-up.
195 Stockpiling of Waste Shingles Prior to Processing General Stockpiling RAS should be accomplished in a way that mini- mizes variability when processed. This requires that RAS from different sources be stockpiled separately and that as many con- taminants as possible are removed prior to grinding. If possible, stockpile on a paved surface to minimize contamination. If a paved surface is not available for storing the RAS, the shingles at the bottom of the stockpile will need to be left in place and not used in the asphalt mixture being produced, since the shingles at the bottom of the stockpile will have become contaminated with the underlying soil materials. Manufacturersâ Waste MW should have little to no contaminants and requires very little clean up. These materials should be inspected when loaded and moved to the paving contractorâs designated loca- tion to ensure that no contamination is present initially and that contamination does not occur during the loading opera- tion. Any possible contamination can often be removed by hand if observed during the loading, hauling, and dumping operations. PC Waste PC waste requires significant clean up prior to use. Most specifications require that a maximum limit somewhere between 0.5% and 3.0% deleterious material be allowed in the asphalt shingles when added to the asphalt mixture. Be aware of the project-specific specification requirements, and make sure that the amount of deleterious material does not exceed the specification limits. It will generally require significant effort to clean the stock- piles so that the RAS meets these requirements for deleterious materials. Materials to be removed may include nails, plas- tics, paper, and wood pieces. The largest particles should be pulled out prior to grinding, since it will be easier to remove them before being broken into small pieces and it will help to minimize damage to the grinding equipment. Once the larger contaminants are removed, the stockpiled RAS should be fairly clean before grinding (Figure D-3). Grinding Equipment Loading Hopper Material is typically loaded into the hopper with a grap- ple crane or front-end loader. The grapple crane is sometimes preferred, since the operator can see the shingles being fed into the grinder and ensure that no contaminants are being obtained from underlying materials. The grapple crane can also pick out any large contaminants and remove them before being placed into the loading hopper. However, a front-end loader is much more maneuverable. The equip- ment (grapple crane or front-end loader) should have an enclosed area to keep the operator free of dust and other airborne materials. Another worker should be present when the hopper is being loaded to identify and remove any additional deleterious materialsâespecially those that may damage the grinding equipmentâprior to grinding. The hopper should be set up to feed the shingles into the grinder at a rate of speed that allows for proper grinding. Conveyor Belt A conveyor belt is commonly used to feed the material from the loading hopper to the grinder. Depending on the setup, this may be a good location to remove some of the del- eterious material. When feeding the material across the belt some of the contaminants will be exposed, making it easy to remove these materials by hand. If contaminants cannot be removed here, the material size will be reduced considerably by grinding, making it more difficult to remove the particles by hand later. It is possible to remove some additional con- taminants, especially with a magnet, after the material passes through the grinder. Grinder Chamber and Cutting Teeth The grinding chamber is where RAS grinding takes place to reduce the particle size to the specified range. The smaller the particle size, the easier it will be to thoroughly mix Source: Krivit 2007. Figure D-3. Clean tear-off shingles.
196 these RAS particles with the other mixture components. However, grinding to a smaller size takes more effort and is costlier. This extra effort and cost is typically more than offset by the improved handling and mixing characteris- tics and the resulting improved performance. Since grind- ing can be more efficient if the material is cooler, it is better to grind during winter months or early morning (Figure D-4). Water is typically used to help reduce the temperature of the materials when grinding RAS, but too much water should not be allowed. Without water, the shin- gles will generate heat, thus decreasing the stiffness of the shingles and increasing the difficulty in grinding the RAS. Higher heat causes the shingles to stick to the screens and other plant components. It also produces more agglomera- tion of the shingles in the stockpiles. Too much water will require additional effort in removing moisture prior to production or during the production process. This addi- tional drying effort will increase heatingâdrying costs and make it more difficult to heat and mix the shingles with the other mixture components. Some contractors hire a subcontractor to provide the grinding service. Other contractors purchase the equipment and perform the grinding themselves. When selecting equip- ment for the grinding operation, there are several things to consider. These include production rate, maintenance requirements, ease of performing maintenance, ability to produce material to desired size, ability to add water, avail- ability of magnet(s), and equipment costs. Grinders typically use compression and abrasion to grind the shingles. There are single-shaft and double-shaft grinders (Krivit 2007). The shingle-shaft grinder is generally less likely to be damaged by contaminants. The dual-shaft grinder is better for reducing the RAS particles to smaller sizes but may be more susceptible to damage. The shredding tips tend to wear and must be replaced regularly (Krivit 2007). An automatic reverse is needed to prevent equipment damage by large, stiff contaminants. Screening Screening RAS particles is necessary during the grinding process to ensure that the proper size is being produced. Grind- ing to smaller particle size results in more effective mixing of the asphalt binder contained in the RAS with the virgin asphalt binder added to the asphalt mixture and with asphalt binder from recycled asphalt pavement (RAP), if used. If thorough mixing does not occur, the asphalt binder from the shingles will not be effective, and the RAP will act more like an aggre- gate and reduce the effective asphalt content in the mixture. A trommel screen (Figure D-5) is typically used to screen the material, and any oversize material is often fed back through the grinding equipment to ensure particles in the finished prod- uct are smaller than the allowable maximum shingle particle size. This is generally a closed loop system with particles below some desired size being removed from the screening operation and sent to the stockpile while the oversize material is fed back through the grinding equipment to further reduce the size. Many agencies require that all RAS particles pass a Â½-in. sieve, but the trend is to grind to smaller sizes. Finer shingle particles improve the mixing efficiency of the asphalt binder from the shingles with the virgin asphalt binder and the asphalt binder from the RAP, if used. Many states are now requiring that a higher percentage of the RAS pass the No. 4 sieve. Exit Conveyor After the shingles have been shredded to the proper size, the material travels up the exit conveyor and is dropped into a pile. The pile should normally not be allowed to be built too high, since the shingles are still warm and may tend to stick together. Equipment should not operate on the stockpile; otherwise, this may compact the RAS, making it more difficult to effectively use. If PC shingles are being used, the exit conveyor is a good point to have a magnet installed to pick up any ferrous material that might still be in the shingles. The stockpile should look very clean and uniform after processing the shingles (Figure D-6). Source: Zhou et al. 2012. Figure D-4. Shingle grinding operation. Source: Krivit 2007. Figure D-5. Grinder followed by trommel screen.
197 Testing Testing shingle particles to determine the RAS charac- teristics is very important. Tests that generally need to be conducted may include particle size distribution, asphalt content, asphalt binder recovery and testing, deleterious material, and asbestos. Particle Size Distribution As previously mentioned, particle size distribution of the shingles is important to ensure that efficient incorporation with other asphalt mixture components is obtained during plant production. The maximum size of the RAS is normally set at about Â½ in. but varies by agency and is smaller for some agencies. Aggregates collected after removing the asphalt binder (ignition or solvent) are also tested to determine the aggregate gradation. The gradation of the aggregate from the shingles will usually have little effect on the over- all aggregate gradation of the mixture, since there will be only 2% to 3% or less of this aggregate in the final blend. However, the amount of dust in the shingle aggregate can be high (around 25%), which can raise the amount of total dust in the mix by between 0.5% and 0.75%. These potential changes in percent passing the No. 200 sieve can be critical, since the mix properties are very sensitive to the amount of material passing the No. 200 sieve. Asphalt Content Asphalt content in RAS is relatively high and must be known to determine its effect on the mix design of the asphalt mixture. In most cases, the amount of asphalt binder in shingles is approximately 15% to 25%, with PC shingles generally having the higher asphalt content. However, the asphalt content will vary considerably, and it is sometimes higher than this range. Asphalt content tests can be con- ducted with the Ignition Test or solvent extraction. If the Ignition Test is used, there is no way to determine the correc- tion factor without conducting some solvent extraction tests for comparison. Some of this comparison has been done, and generally it has been found that the correction factor is very low. Hence, for most RAS, there is not much error in using the Ignition Test to measure asphalt content without applying a correction factor. Asphalt Binder Recovery and Testing Some agencies require asphalt binder in a RAS mixture to meet certain properties. In this case, it is necessary that the asphalt binder be recovered and tested to determine its properties. Even if there are no requirements on the blended asphalt binder properties, it is a good idea to occasionally recover and test the RAS binder. If the RAS binder proper- ties are too stiff, this may require that the virgin binder be adjusted so that the properties of the combined binder are satisfactory. Sometimes recovering and testing the aged binder from the RAS can be difficult, since it can be extremely stiff. In some cases, a soft asphalt binder or rejuvenator is used to soften the RAS/virgin binder and this often pro- vides improved binder properties. However, if a softer material is added to the asphalt mixture, thorough mixing is required; otherwise, there can be some of the produced mixture that is excessively soft. Unfortunately, it is difficult to know when the materials have been thoroughly mixed, resulting in a homogenous mixture. Deleterious Material There are limits on how much deleterious material can exist in a RAS stockpile. Even though great care must be taken in removing deleterious materials before the grinding process, some contamination will certainly occur but this needs to be kept to a minimum. Samples of the stockpile should be tested to ensure that deleterious material percent- ages are not excessive. The typical range allowed is 0.5% to 3.0%, so check the project specifications for the actual requirements. Asbestos Asbestos was used in asphalt shingles until the mid to late 1970s. There is no asbestos in present-day production of asphalt shingles and, therefore, no need to be concerned with asbestos if MW is being used. However, if PC waste is used, Source: Aggregate Recycling Corporation 2014. Figure D-6. Processed shingles.
198 there is usually a need for asbestos testing. Keep in mind that local, state, and federal requirements may vary. Some require- ments do not consider the RAS to contain asbestos unless the amount of measured asbestos is above 1%. Testing conducted to date shows that most PCâRAS shows no asbestos or an insignificant amount. A small percentage of tests, however, do show minor amounts of asbestos. Many contractors tend to test their stockpiles for asbestos even if there is no require- ment to do so. These test results can be useful if some issue arises in the future related to potential asbestos problems. It is a good practice to develop a testing plan for asbestos. If no asbestos is found for several consecutive tests, then the rate of testing can be reduced. Stockpiling Processed Shingles Moisture It is important to keep RAS dry when stockpiling. The shingles have been shredded to a very fine size, allowing them to absorb and retain high water content. Wet shingles are difficult to dry and heat to ensure proper integration with other mixture components. It is preferred that RAS be kept under cover to prevent high moisture content occur- ring from rainfall (Figure D-7). Also, some moisture is likely added during RAS processing and needs to be limited to pre- vent potential problems. Equipment Concerns on Stockpiles It is important to keep equipment off of the stockpiles after the RAS has been processed. Equipment operating on stockpiles can result in a number of issues, including addi- tional breakdown of the shingles, contamination, and some segregation in the shingle stockpile, especially when blended Source: Zhou et al. 2012. Figure D-7. Covered processed RAS. with other components, such as RAP or sand. The equipment will also result in some compaction of the shingles, which may make it difficult to remove the RAS from the stockpiles. When the RAS is removed, it may tend to agglomerate, mak- ing it difficult to feed uniformly into the mix and produce a consistent mix quality. Mixing Shingles and Sand or RAP There are many cases where shingles are blended with sand or RAP to prevent the RAS from sticking together in the stockpile. This facilitates handling but creates problems in ensuring good mixing of components and guaranteeing that segregation in the mixed material does not occur. Some con- tractors believe that mixing the shingles with RAP or sand is not necessary to prevent sticking together, but others believe that it is necessary. To facilitate handling, paving contractors often add the RAS through a feeder and feed it straight to the mixing area without mixing with other components. Some have also mixed the RAS with a synthetic zeolite to minimize agglomerations (West 2015). Clumping of material is nor- mally a bigger problem in hotter rather than colder climates. When mixing the RAS with sand or RAP, it is necessary to include these other components in the testing and mix design. It is also important to ensure good mixing practices when combining RAS with sand or RAP. The best practice for mix- ing is to use two feeders that feed onto a common belt. This will provide uniform and accurate blending of the two mate- rials. Mixing with a loader on the ground surfaceâor even on a paved surfaceâis not a good approach to obtain a uniform mix, and this method of mixing is not recommended. If uni- form mixing is not obtained, this will affect the uniformity of the completed project. The specific gravity of the RAS and the sand or RAP can be significantly different, and this can cause segregation of the materials when handling. Segregation after mixing must be minimized. Adding the RAS separately into the mix without premixing with other materials is preferred, since this will minimize concerns with producing a homog- enous mix to feed into the plant. Bibliography Aggregate Recycling Corporation. Ground Shingle Stockpile. Eliot, Maine. https://www.aggregaterecycling.com/images/resized-IMG_ 0450.jpg. Accessed June 26, 2014. Construction and Demolition Recycling Association. Asbestos in Asphalt Shingles. 2004â2018. http://www.shinglerecycling.org/ content/asbestos-asphalt-shingles. Hansen, K., and A. Copeland. Asphalt Pavement Industry Survey on Recycled Materials and Warm-Mix Asphalt Usage: 2014. National Asphalt Pavement Association, Lanham, Md., 2015. Krivit, D. Recycling Tear-Off Asphalt Shingles: Best Practices Guide. Construction Materials Recycling Association, Eola, Ill., 2007.
199 National Association of Home Builders. From Roofs to Roads: Recycling Asphalt Roofing Shingles into Paving Materials, 1999. http://www. wastexchange.org/upload_publications/RecyclingRoofingWastes.pdf. Northeast Recycling Council. Asphalt Shingles Manufacturing and Waste Management in the Northeast. Fact sheet. 2012. West, R.C. Best Practices for RAP and RAS Management. National Asphalt Pavement Association, Lanham, Md., 2015. Wojahn, B. Nikko Ganacias of Northwest Shingle Recyclers. The Oregonian. Portland. http://media.oregonlive.com/pdxgreen/ photo/shingles1-9jpg-efa50a45e001f89e.jpg. Accessed June 26, 2014 Zhou, F., J. W. Button, and J. Epps. Best Practice of Using RAS in HMA. Report 0-6614-1. Texas Transportation Institute, Texas A&M University System, College Station, 2012.