22 SPRING/SUMMER 2023 to the production facility, and the manufacturing process. The extractional upstream production (A1) uses industry-wide EPDs and LCAs for background data, not source-specific EPDs. For example, extracting asphalt binder from crude oil does not distinguish between crude sources, refinery plant designs, or transport of the crude oil to the refinery or the terminal. Though the asphalt binder industry is developing an EPD program, no EPDs for asphalt binders have been published to date. The same can be said for aggregates and many of the additives used. For reclaimed asphalt pavement (RAP), the Emerald Eco-Label program uses a default fuel consumption value to account for the energy and emissions associated with processing, as specified in the PCR for asphalt mixtures. However, the effective use of RAP in new asphalt mixes reduces the material cost by replacing the amount of virgin aggregates and binder. Likewise, this saves on the environmental cost by substituting for asphalt binder and aggregate. The asphalt mix design comprises three main components: virgin asphalt binder, virgin aggregates, and recycled materials (i.e., RAP, reclaimed asphalt shingles, ground tire rubber, plastics, etc.). From discussions with contractors who have developed EPDs for some of their mixes, we have learned that the amount of virgin asphalt binder required for a mix design can increase or decrease the GWP on comparable mixes (i.e., surface mixes with ½” nominal maximum aggregate size and PG 64S-22 binder). Since the standard dataset used for asphalt binder includes all processes up to and including terminal operations, EPDs for asphalt mixtures do not differentiate supply chain-specific differences between asphalt binder suppliers. Therefore, EPD results scale with the virgin asphalt binder content of the mix. However, if the asphalt binder in RAP can offset a portion of the added virgin binder, then the asphalt binder used decreases. The same can be said for replacing virgin aggregates with RAP aggregates. Transport to the factory (or A2 on Figure 4) will be an important factor in the EPD, depending on the location of the asphalt plant. Simply put, the A2 deals with the trucking, railing, or barging of upstream materials, primarily aggregates and asphalt binder. For asphalt plants that sit in a quarry, aggregate transport is minor in terms of energy consumption. However, a standalone plant supplied only by haul trucks will have a much higher A2 depending on the length of haul. The same can be said for plants supplied by a rail line or barge. For RAP, transport of the material is accounted for from the initial storage or processing location. Transport of RAP from the milling site to the initial storage or processing location is part of the previous pavement’s life cycle and is not included in the EPD. Therefore, virgin aggregate and asphalt binder offset using RAP will reduce the A2 impact on the overall EPD for most plants. Another consideration is projects where non-polishing aggregate must be transported for use in asphalt surface mixes, which will cause the A2 to be higher. Finally, several lessons can be found in the manufacturing (or A3) stage of the life cycle. The A3 stage relies heavily on the burner fuel type and quantity used to produce one ton of mix. Some fuels, such as natural gas, burn much cleaner than diesel. Fuel consumption can be reduced through burner tuning and managing aggregate moisture content. The fuel needed to dry the aggregates or drive off moisture is critical. NAPA’s QIS-126 publication “Energy Conservation in HotMix Asphalt Production” shows that paving and sloping the stockpile areas can help reduce moisture in aggregates. Covering stockpiles, particularly RAP, high absorption aggregates and fine aggregates, keeps the materials dry. The drier the input materials to the drum, the less heat is needed, thus improving EPD results by reducing fuel consumption. Other areas to reduce fuel usage are burner efficiency, drum flighting, and baghouse performance. While all of these are common sense, EPDs can help plants benchmark and quantify the environmental benefits of operational improvements. Understanding which parameters affect the EPD is crucial for a contractor. The contractor will learn the drivers that increase or decrease the EPD results and areas of cost savings and efficiencies. For example, some plants may not have the ability to switch fuel sources, but paving stockyards and covering stockpiles can have a huge benefit. In addition, running plants at lower temperatures can minimize fuel use and reduce the A3 impacts and fuel costs. How Does This Apply to Concrete? The most common question asked at asphalt meetings regarding EPDs is, “What about concrete?” It seems like a straightforward question since engineers are accustomed to comparing thickness designs, unit costs, and performance. However, it is not that simple at the moment. The units for concrete are cubic meters, and short tons are used for asphalt. Not a big deal—we can make the conversions for a set thickness design using unit weights. But dig a little deeper: are the system boundaries, background datasets, and other key parameters for asphalt and concrete the same within the PCRs? Unfortunately, the answer is no. Until these parameters are harmonized across different PCRs, comparing EPDs for different pavement material types is problematic. △ continued from page 21 CAN YOU SPELL EPD? EPDs are another metric to show a material’s environmental and economic advantages. Like putting together the first cost for a project, the first EPD for a mix or plant will take time. However, once the information is gathered, processed, and input into the Emerald Eco-Label program or other verified processes, the next iterations of EPDs will take less time.
RkJQdWJsaXNoZXIy Nzc3ODM=