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Shingle-minded purpose: research in Minnesota has focused on market development for recycled asphalt shingles.

A two-year research and development project that examined the recycling of post-consumer asphalt shingles was recently completed and looked at three key components of any such recycling endeavor:

* An analysis of environmental regulations and securing a clean, certified source of supply of tear-off shingles;

* Processing, including a dust management program; and

* End-use application into hot-mix asphalt (HMA) as paving for road construction in St. Paul, Minn.

The Minnesota Department of Transportation (Mn/DOT) was the lead technical research agency in the project, which was funded by the Recycled Materials Resource Center (RMRC) at the University of New Hampshire.


The RMRC's recycled asphalt shingles project (RMRC Research Project No. 22) included a series of controlled tests that demonstrated the feasibility of using tear-off (or post-consumer) scrap shingles. This field demonstration using tear-off asphalt shingles culminated over two years of research and market development.

* This RMRC Project included a one-time demonstration in the fall of 2003 of the use of residential tear-off asphalt shingle scrap. Construction Materials Recycling Association (CMRA) member Bituminous Roadways Inc. (BRI) conducted this demonstration.

BRI, which already processed shingle waste from a manufacture's turer's plant, for use in HMA, received the tear-off shingle scrap from Sela Roofing and Remodeling Inc. Sela's re-roofing jobs were selected to restrict the material to private, residential homes. Armor Waste hauled the mixed roofing waste via roll-off boxes to its Eagan, Minn., transfer station. There, the material was tipped and sorted by Armor crews. Shingle scrap was separated from other roofing waste via hand sorting and a skid-steer loader.

The hauling, tipping and sorting operations used for the demonstration were the transfer station's normal procedures for handling loads of mixed roofing waste. Minor amounts of nails and roofing felt remained in the product shipped to BRI. The final asphalt shingle loads sent to BRI were very dean, without any significant contamination.

BRI received approximately 50 tons of certified, residential tear-off asphalt shingle scrap from Armor at its Inver Grove Heights, Minn., pit and asphalt plant. BRI stockpiled the tear-offscrap separately from its manufacturer shingle scrap. The tear-off scrap was ground and screened twice to assure removal of all nails. The resulting recycled asphalt shingle (RAS) product was stockpiled separately from the manufacturer RAS product.

The tear-off RAS product was incorporated at 5 percent by weight into about 1,000 tons of HMA. The tear-off-shingle-derived HMA was then installed by BRI crews at approximately 2 inches thick as base course within a residential road reconstruction project in St. Paul. Only the base course of the northbound lanes of the road project utilized tear-off-derived HMA. As the control for comparison, southbound lanes utilized the same grade of HMA using 5 percent manufacturer's shingle scrap. All other mix design and quality assurance/quality control (QA/QC) parameters remained the same. The final wear course was installed in the spring of 2004 and included manufacturer derived HMA only, no tear-off-shingle scrap was incorporated into the wear course.

BRI reported that there were no differences in HMA production or pavement installation, although there was approximately 1 percent more asphalt cement (AC) recovered in the tear-off-derived HMA. This somewhat explains the lower air voids in the tear-off-derived HMA and the higher density in the field as shown in core results. This is as expected, given that tear-offs typically have an asphalt cement (AC) content around 30 percent to 40 percent as compared to manufacturer product which is around 20 percent AC. However, BRI estimates that less than 50 percent of the asphalt in the RAS is effective in the mix. The reminder of the RAS probably performs as an asphalt coated aggregate. BRI also reported that there were no differences in paving operations. No debris in the final HMA pavement product was detected.

BRI has stated that when selecting a virgin binder grade for the HMA mix design, adjust one temperature interval lower when using RAS. For example, if the HMA specifications for the job requires a PG 64-22 grade, adjust to a PG 58-28 virgin binder if using 5 percent RAS. BRI has continued to expand its use of RAS in more of its mixes.

BRI set a record in 2004 for its recycling of manufacturer shingles in part because of new 2003 wording in the Mn/DOT materials specifications that is more permissive towards use of manufacturer shingle scrap in HMA.


The RMRC project started by conducting a thorough review of the available literature on asphalt shingle recycling. Technical, environmental and trade publications were reviewed. Environmental data reviewed included studies summarized in the "Asphalt Roofing Shingle Recycling Assessment Project" (ARSRAP) recently completed by the CMRA. The CMRA sponsored the project in conjunction with the University of Florida, Gainesville, Fla., the National Roofing Contractors Association (NRCA) and the U.S. EPA (Region Five, Chicago).

The federal National Emission Standards for Hazardous Air Pollutants (NESHAP) asbestos regulations, as promulgated by the U.S. Environmental Protection Agency (EPA), provide the primary regulatory framework for roofing waste disposal. (Links to this rule and other NESHAP advisories can be located at asp). The ARSRAP survey indicated that, from a variety of studies throughout the country totaling 5,250 samples, only three samples contained asbestos above NESHAP standards. Samples detected with asbestos fiber greater than 1 percent are defined by NESHAP as asbestos containing material (ACM). The ARSRAP survey calculates to a frequency of about 0.06 percent of total samples of "hits" with ACM. Other sampling programs have been conducted with similar results--essentially no detectable asbestos. The previous studies indicate that any ACM "hits" are more likely from commercial buildings or contamination of the shingles from the mastic, caulk or felt.

Tear-off asphalt shingles from private, residential structures, including single-family homes up to "four-plexes," are generally exempt and not regulated under NESHAP. One exception to this exemption is that used roofing shingles may be regulated if the building structures are commercial or institutional buildings, owned by a government agency or otherwise defined as "facilities" under NESHAP.

The RMRC project team formed an environmental review committee. This committee determined that if there were to be any new exposures to asbestos it would be at the point of grinding tear-off shingles. The U.S. Occupational Safety and Health Administration (OSHA) regulates occupational exposure to asbestos. OSHA's general industry regulations specify the permissible exposure limit (PEL). The project team subcontracted with Applied Environmental Sciences, Inc. (AES), an environmental lab and consultant, to perform on-site air sampling at the BRI shingle recycling plant in Inver Grove Heights, Minn. AES performed airborne "total fiber" sampling on two different days.

The AES air sampling and lab analysis of "total fiber" essentially simulated the potential "worst case" asbestos exposure to BRI employees as if a rare incidence ACM shingle load was processed. It is important to note that BRI was grinding manufacturer shingle scrap only at the time of these air sample tests. Shingles have a high fiberglass and cellulose component such that "total fibers" can be measured in this way. The key operating assumption was that if the measured "total fiber" in the NESHAP-regulated asbestos fiber size range was less than the asbestos PEL, then the rare ACM load that might get processed would not expose staff above the asbestos PEL.

AES performed standard OSHA personal monitoring on the two BRI workers and placed three stationary samplers in locations of maximum dust to test worst-case conditions. The intent was to determine if any air borne fiber from the grinding and screening operations where the BRI employers were working exceeded OSHA limits. AES sampled and analyzed for "total fibers" in the NESHAP-regulated asbestos size range.

On the two days that AES sampled for "total fiber" in the asbestos size range, the eight-hour PEL was not exceeded. The peak exposure was seen when the grinder operator was cleaning equipment and raised considerable dust. Therefore, wet methods were recommended for this cleaning.

Based on this study, AES concluded that it would be highly unlikely that the OSHA standards would be exceeded even if a slug of ACM shingles were to be processed.

The Minnesota Department of Labor and Industry, Occupational Safety and Health Division (MN OSHA) initiated a similar field study three years earlier at the same BRI plant on Oct. 5, 1999. The two BRI shingle recycling plant employees were equipped with personal dust sampling monitors. The "worst case" air concentration of particulate "total dust" did not exceed the OSHA PEL standard. It is important to note that this MN OSHA sampling and investigation occurred during a period of BRI shingle recycling operations when a different grinder make and model was being utilized. BRI installed its new Bandit "Beast" grinder model in the spring of 2001.

Like many shingle recyclers, BRI utilized water on the feedstock just before the grinding chamber to help with cooling and control dust. BRI added customized shrouding to its horizontal grinder to further help control dust and blowing debris.

As one means to avoid unnecessary sampling requirements, the roofing company and hauler that supply the shingle recycling operations should certify in writing that:

* The tear-off shingles are asphalt shingles only (such as three-tab shingles), from private, residential homes only having four or fewer dwelling units per building;

* These residential buildings are not "regulated facilities" according to state and federal rules;

* The material delivered consists of asphalt shingles only and contains no known hazardous material; and

* The loads of shingles are free of prohibited materials, including: cementitious shingles, other non-shingle debris (e.g., transite siding, etc.), and other trash or hazardous waste.

If the roofing company and hauler can provide such certification, the shingle recycler should then be able to certify in writing to its customers that the RAS processed and utilized in HMA installed for road construction projects is derived from eligible shingles only. The recycler should be able to certify that all tear-off shingle scrap came from certified suppliers only and that the final product contains no known hazardous material.

The shingle recycler may be equipped to sort mixed roofing waste as part of the recycling operations. But if not, the roofing companies and/or haulers that sort shingles for delivery will need clear specifications for what is acceptable and not acceptable to the shingle recycler. A standard of "clean asphalt shingles only" should be established with a clear definition (e.g., certified loads with minimum non-shingle debris). The list of roofing waste items that should be specifically excluded are: cementitious shingles; other non-shingle debris (e.g., transite siding, etc.); wood; metal flashings, gutters, etc; plastic wrap; plastic buckets; paper waste; and any other garbage or trash.


The shingle recycling industry is making rapid strides towards full-scale implementation of shingle recycling. It is clear that developers have their sights set on the much larger volume of tear-off scrap. There are several ongoing initiatives to further develop the market for recycled asphalt shingles (RAS). The American Association of State and Highway Transportation Officials is in the process of adopting a generic materials specification that will provide for the engineering standards needed to guide processing and utilization of both manufacturer and tear-off RAS into HMA. (See sidebar on p. 30.)

The CMRA is in the process of updating its Web page, Hopefully, many of the recent studies and research projects that have been published on shingle recycling over the past two years can be posted on this site that continues to serve as a major clearinghouse of information.

The Minnesota Office of Environmental Assistance has recently funded a laboratory study for Mn/DOT at the University of Minnesota Department of Civil Engineering. The engineering performance of tear-off-shingle-derived HMA will be compared to manufacturer-derived HMA. In addition, the Missouri Department of Transportation is conducting a similar, parallel lab study to compare tear-off-derived HMA to HMA made with only recycled asphalt pavement.

The prospects are bright for this promising recycling technology. These ongoing research and development efforts should help continue to accelerate its safe and profitable implementation.


* Even though fiber sampling tests have indicated no violations of OSHA standards for shingle grinders, the observations indicate that shingle recycling operators should develop dust/fiber management and employee hazard prevention plans as a part of a larger occupational health and safety plan.

This plan can include regulated requirements and common sense tactics to avoid unhealthy employee exposure to any fugitive dust that may be generated during recycling operations.

This dust and fiber management plan should include at a minimum: employee education also proper equipment operation and feedstock quality control; continuous watering of shingle feedstock as it enters the grinding chamber; wet cleaning of equipment; and installation and maintenance of shrouds to contain any fugitive dust or debris.

Operators may also want to consider enclosed, air-conditioned cabs for front-end loaders. Personal particulate respirators for grinder operators may be necessary and prudent during especially dirty equipment cleaning procedures.

These type of precautions should :be in addition to normal safety requirements for employees, such as the use of standard, industrial workplace protective gear like hard harts, gloves, eye protection, dust mask, long sleeves and pants and boots.


* The American Association of State and Highway Transportation Officials (AASHTO) and its Subcommittee on Materials (SOM) are in the final stages of adopting a materials specification that itemizes specific quality assurance/quality control requirements for utilizing manufacturer and tear-off shingle scrap in HMA.

Detailed requirements include:

* The final RAS product must be sized and screened such that 100 percent passes the 1/2 inch sieve screen;

* Maximum addition rate contractor option;

* Gradation must meet the requirements of the mix design;

* Deleterious material must not exceed a maximum of 0.50 percent by weight cumulative total (i.e., combination of all: metal, glass, paper, rubber, wood, nails, plastic, soil, brick, tars and other contaminating substances); and

* Asbestos level established by the state or U.S. EPA.

AASHTO is a nonprofit, nonpartisan association representing highway and transportation departments in the 50 states, the District of Columbia and Puerto Rico. Its primary goal is to foster the development, operation and maintenance of an integrated national transportation system.

The AASHTO SOM is expected to decide on this proposed recycled asphalt shingle product specification at its next meeting, which is scheduled for Aug. 8-12, 2005, in Santa Fe, N.M. Additional information about this Subcommittee on Materials meeting is available online at nsf/8752a29ff17747a28625698b0067e846.

The author is a consultant with Dan Krivit and Associates and can be contacted at
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Article Details
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Title Annotation:Asphalt Shingle Focus
Author:Krivit, Dan
Publication:Construction & Demolition Recycling
Geographic Code:1USA
Date:Jul 1, 2005
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