Sustainable Materials Management
The world continues to grow, and with growth in population and economic output comes growth in demand for resources. The way these resources and materials are managed must be continuously critiqued and re-evaluated so that future environmental impacts are minimized while meeting current needs.

Sustainable Materials Management, or SMM, is the idea or action being taken by government agencies and private companies to look closer at how they are managing their materials and the environmental impacts of these materials. At its essence, SMM goes beyond the idea of “cradle to grave” and assures that materials are being used to their fullest extent while minimizing their impact on the environment [1].

SMM of materials in the built environment is on the top of the EPA’s SMM strategic plan for 2022. One action is to bring SMM to the forefront whenever constructing or demolishing in the built environment with the goal of creating incentives and policies for the “safe reuse and recycling of C&D materials” [2]. SMM quantitatively measures the impacts of materials through identifiers such as greenhouse gas (GHG) potential, water consumption, virgin resource use, and more. Quantitatively measuring the effects of these actions and their anticipated outcomes allows current policy makers, material managers, and the public to make informed decisions about how to manage asphalt shingles in the present.

WARM
Life Cycle Analysis (LCA) tools are used to quantitatively evaluate SMM practices. The Environmental Protection Agency (EPA) provides the Waste Reduction Model (WARM) for this purpose. WARM is an LCA tool which permits users to evaluate the energy and GHG implications associated with end of life management of materials [3].

Asphalt shingles are one of the many materials accounted for in WARM. It accounts for management practices of landfilling, combustion, recycling, and source reduction of asphalt shingles. WARM can also account for composting and anaerobic digestion but does not do so for asphalt shingles due to the absence of organic material [4].

Fiberglass mat-based shingles are highly prevalent in the residential shingle market, and because of this, WARM calculates environmental impacts based on manufacturing and management practices for fiberglass mat-based shingles alone [5].

In WARM, the life cycle boundaries for each management practice of asphalt shingles starts from the deconstruction of a roof rather than the manufacturing of a shingle. This is because WARM is meant to compare material management practices at the end of life of the material (i.e. deconstruction of a roof) rather than the life of the material itself (i.e. manufacturing of the shingle). Based on this method, a shingle that has not been disposed would have net zero impact on the environment. The following sections describe and show the assumptions and impacts associated with each management practice for asphalt shingles.

Landfill
Disposal at a landfill requires transport from the waste generation point to the landfill and processing at the landfill site. In the landfill, materials with biogenic carbon (e.g. newspaper, food waste, wood, etc.) are anaerobically decomposed and produce methane gas that can be collected and used for energy or flared off. Some parts of these materials do not fully decompose and remain stored in the landfill, thereby acting as a carbon sink (i.e. an artificial or natural reservoir that stores carbon) [4].

Asphalt shingles do not biodegrade and therefore do not produce methane or act as a carbon sink. The only impact accounted for is the emissions associated with transportation to and processing at the landfill. This results in a net emission of 0.02 MTCO2E/Short Ton of asphalt shingles landfilled [5]. The environmental protection agency (EPA) estimates 11 million tons of asphalt shingle waste is generated annually in the US [5]. The emissions associated with landfilling all 11 million tons of asphalt shingle waste is equivalent to putting nearly 47,000 additional passenger vehicles on the road for one year or adding the energy use of nearly 23,750 additional homes for one year.

Combustion
Combustion of materials requires transport from the waste generation point to the combustion facility. WARM considers the combustion of non-biogenic materials to contribute to carbon dioxide emissions since they would not naturally release carbon dioxide when combusted or decomposed under natural conditions. The combustion of nitrogen containing compounds contributes to the release of nitrous oxide which has a global warming potential higher than carbon dioxide. Offsets from combustion result from the generation of electricity (thereby avoiding emissions from utilities) and recovery of metal from combustor ash [4].

In the U.S., asphalt shingles (and C&D in general) are assumed to not be combusted at standard facilities due to contamination in incoming materials. In WARM, impacts of shingle combustion are calculated based on combustion at cement kilns. Therefore, rather than offsetting electrical utilities, combustion offsets fuel that would otherwise fuel a cement kiln. Shingles do not contain ferrous material that could be recovered from combustor ash, and therefore there are no savings associated with recycling ferrous material from the ash. This results in a net savings of 0.36 MTCO2E/Short Ton of asphalt shingles combusted [5]. Compared to landfilling, combusting all 11 million tons of asphalt shingles generated annually is equivalent to taking nearly 800,850 passenger vehicles off the road for one year or saving the energy use of nearly 403,840 homes for one year.

Recycling
The EPA defines recycling as “the separation and collection of wastes, their subsequent transformation or remanufacture into usable or marketable products or materials, and the purchase of products made from recyclable materials.” Recycling can be generalized into two methods: closed-loop and open-loop recycling. The majority of products evaluated by WARM are closed-loop (e.g. recycled asphalt shingles being made into new asphalt shingles) while other materials are evaluated as open-loop (e.g. asphalt shingles being manufactured into hot mix asphalt). For both methods, environmental impacts are calculated based on emissions related to the recycling processes and the saving of virgin materials as a result of the recycled product. WARM looks only at the environmental impact associated with collecting and recycling the material and offsetting virgin material demand. It does not evaluate how recycling the material may increase demand for the recycled product (e.g. hot mix asphalt with asphalt shingles) due to them becoming more economically priced [4].

Shingles can be recycled in a number of ways including use in hot mix asphalt (HMA), use in new roofing shingles, mulch, or road base. Currently the closed-loop recycling of asphalt shingles (creating new shingles from old shingles) is still in developmental stages, and the most common practice is open-loop recycling with recycled shingle use in HMA. Therefore, WARM assumes that all recycled shingles are used to replace virgin asphalt and aggregate material. WARM assumes a 22% asphalt cement and 38% aggregate content in asphalt shingles. This composition is then used to estimate the savings generated from not manufacturing and transporting virgin asphalt cement and aggregate for use in HMA. WARM also assumes that 7.2% of incoming asphalt shingles is lost as residue during the recycling process and therefore does not contribute to the offset of virgin asphalt cement or aggregate. This results in a net savings of 0.09 MTCO2E/Short Ton of asphalt shingles recycled [5]. Compared to landfilling, recycling all 11 million tons of asphalt shingles waste generated annually is equivalent to taking nearly 164,880 passenger vehicles off the road for one year or saving the energy use of 83,140 homes for one year.

Alternative Asphalt Shingle LCA
WARM is meant to be a streamlined tool with the primary purpose to provide information on climate change impact by measuring energy and GHG implications for end of life management of a material. WARM does not measure impacts to health, air, water, and other environmental impacts, and it does not provide a full environmental evaluation [2].

Shingle manufacturers, such as Owens Corning, have issued environmental product declarations (EPD) which is a report that aims to list out a product’s impact on the environment throughout its lifetime [6]. The lifetime boundaries included production and disposal (either transportation to a recycler or landfill) but not the construction or use stage. Though it cannot be compared to the WARM LCA, it provides another look at the environmental impact of asphalt shingles. Owens Corning performed the LCA using data from their own shingle production in 2012 as well as life cycle inventory data from ecoinvent and US-EI. In the report, environmental impacts such as acidification, eutrophication, smog, and ozone depletion were evaluated. Please reference the report for a full overview of the LCA inventory and boundaries [6].

Environmental Concerns
In addition to concerns over energy use and GHG emissions during shingle disposal, there are health and environmental concerns with asphalt shingles as well. One area of concern is the release of polycyclic aromatic hydrocarbons (PAHs) from petroleum components of the asphalt shingles. PAHs are a group of hydrocarbons formed from the incomplete burning of organic substances (e.g. petroleum) that can be released into the environment and stored in the kidney, liver, and fat of humans [7]. “Many PAHs are harmless, but some may be reasonably expected to be carcinogenic” [7]. With asphalt shingles, PAHs may leach into water during stockpiling or into the air during HMA production. However, based on limited studies on leachability, PAHs are not expected to “readily leach” into the water. PAHs are already known to be released during production of HMA and there are regulations that monitor these emissions. The use of RAS in HMA is not expected to significantly add to the release of PAHs during HMA production [7]. A 2013 study by the University of Wisconsin-Madison looked at the leachability of heavy metals from a RAS and coal fly ash mixture. Such a mixture could be beneficially used as structural fill for highway construction. The study concluded that RAS did not increase contaminants in the leachate with coal ash leaching more contaminants [8].

Another area of concern is asbestos in asphalt shingles from older houses or sources. If a shingle contains asbestos and is recycled, the asbestos fibers can become airborne during the shingle grinding process and negatively impact a worker’s health. NESHAP prohibits recycling (i.e. grinding) asphalt shingles that contain asbestos, and many states require testing of asphalt shingle samples for asbestos before recycling. Other states may not have explicit regulations but stress that it is better to follow best practice guidelines and check first than to be found in violation of NESHAP later on [7,9]. Use of asbestos in asphalt shingles was phased out in the early 1980’s and testing of over 27,000 tear-off samples returned positive as an asbestos containing material in 1.5% of the samples. It is expected that asbestos will be even less prevalent in tear off asphalt shingles over time given the lifetime of asphalt shingles [7]. Nevertheless, asbestos testing helps to ensure the safety of people in the vicinity of asphalt shingle grinding operations.