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Using Recycled Asphalt Shingles with Warm Mix Asphalt Technologies (2018)

Chapter: Chapter 6 - Economic Analysis of Asphalt Mixtures Containing RAS

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Page 138
Suggested Citation:"Chapter 6 - Economic Analysis of Asphalt Mixtures Containing RAS." National Academies of Sciences, Engineering, and Medicine. 2018. Using Recycled Asphalt Shingles with Warm Mix Asphalt Technologies. Washington, DC: The National Academies Press. doi: 10.17226/25185.
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Page 138
Page 139
Suggested Citation:"Chapter 6 - Economic Analysis of Asphalt Mixtures Containing RAS." National Academies of Sciences, Engineering, and Medicine. 2018. Using Recycled Asphalt Shingles with Warm Mix Asphalt Technologies. Washington, DC: The National Academies Press. doi: 10.17226/25185.
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Page 139
Page 140
Suggested Citation:"Chapter 6 - Economic Analysis of Asphalt Mixtures Containing RAS." National Academies of Sciences, Engineering, and Medicine. 2018. Using Recycled Asphalt Shingles with Warm Mix Asphalt Technologies. Washington, DC: The National Academies Press. doi: 10.17226/25185.
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Page 140

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138 Economic Analysis of Asphalt Mixtures Containing RAS Ideally, an economic analysis of using RAS in asphalt mix- tures would consider the full life-cycle costs, which would include initial cost savings from using the recycled material, as well as the impact that the material may have on the main- tenance and service life of the asphalt layer. However, at this time, there is insufficient information on the maintenance and long-term performance of mixtures containing RAS rel- ative to mixtures without RAS. Therefore, this section only provides an analysis of the potential initial economic savings to produce RAS mixtures. Factors affecting the initial cost of mixtures containing RAS include the tipping fee for accepting RAS, processing and handling costs for RAS, and the reduction in amount of virgin asphalt and aggregate required for the mix. However, the savings that the contractor realizes may or may not be passed on to the state DOT. The portion of savings passed on to the agency will depend on competition among contractors, the amount of work available, and many other factors. In the low bid system, contractors will keep as much of the savings as they can and still win the project. For this analysis, the potential savings for using RAS is esti- mated in the following equation: Savings ton RAS% P F $ ton P $ ton $ ton $ ton (6-1) bRAS RAS virgin asphalt sRAS virgin agg. P&H tip [ ] ( ) ( ) ( ) = × × + × − − where: Savings/ton = potential savings per ton of asphalt mixture; RAS% = percent of RAS used in the asphalt mixture; PbRAS = asphalt content of the RAS; FRAS = so-called RAS availability factor, or per- cent of the RAS binder considered effec- tive in replacing virgin binder; $/tonvirgin asphalt = cost per ton for virgin asphalt binder; PsRAS = the percentage of aggregate granules in the RAS; $/tonvirgin agg. = cost per ton of virgin fine aggregate; $/tonP&H = RAS processing and handling cost per ton; and $/tontip = tipping fee received for RAS. In cases where the contractor purchases processed RAS as a ready-to-use material, then the savings would be calculated with the equation above with the RAS purchase price used in place of $/tonP&H and the tipping fee, $/tontip, would be zero. As noted in Table 1-1, of the state highway agencies that currently allow the use of RAS, specifications differ consider- ably with regard to the amount and type of RAS. Most states allow from 3% to 5% RAS in asphalt mixtures. For the fol- lowing analysis, the percentage of RAS used in mixtures was evaluated at 3% and 5%. The asphalt content of RAS can vary from about 15% up to about 35%, but typical asphalt content is about 20%. As noted in Chapter 1, PC–RAS will typically have higher asphalt content than MW. In this analysis, the asphalt content of RAS was evaluated at 20% and 30%. The RAS availability factor is an assumed value based on individual agency practices. Some agencies consider 100% of the RAS asphalt as effective; others assume a lower percent- age. The old AASHTO PP 58 included a method to calculate an availability factor, but that method has been disputed. It is common for agencies to assume that 75% of the RAS binder is effective in replacing virgin binder. In this analysis, cost sav- ings were estimated assuming 100% and 75% for FRAS. Since 2014, the price of unmodified asphalt binder has ranged from about $320 to $620 per ton (approximately $320 in early 2017 and $620 in 2014). The analysis was conducted based on the cost of virgin asphalt at $300 and $600 per ton. The savings from the RAS aggregate is very small compared to savings from asphalt binder replacement. RAS typically con- tains up to 40% mineral aggregate (granules). The percentage C H A P T E R 6

139 of aggregate granules in PC–RAS will typically be lower. For an estimate of the range of potential savings associated with the RAS aggregate, assume that the RAS contains 35% granules, the virgin aggregate cost is $20 per ton, and 3% to 5% RAS is used in the mix. At a 3% RAS content, the estimated savings is .03 × .35 × $20 = $0.21 per ton of asphalt mix. At a 5% RAS content, the estimated savings is $0.35 per ton of asphalt mix. RAS may also provide an economic benefit if the RAS eliminates the need to add other fibers to the mix. RAS has been added to stone matrix asphalt and open-graded mixes on a few projects to replace the fibers used to minimize drain- down of the asphalt binder between the time of mixing and placement (Riggs 2015). In general, the use of RAS for this purpose has been successful. An estimate of the savings from eliminating cellulose fibers in open-graded friction course and stone matrix asphalt mixtures was $2.85 and $2.20, respec- tively (Watson 2017). The difference in savings is attributed to a higher dosage rate for cellulose fibers in open-grade fric- tion courses compared to stone matrix asphalt. These savings include the materials, delivery, and handling (feeding) costs associated with the cellulose fibers. The cost for processing RAS can vary considerably but $10 to $25 per ton is a reasonable range. Some agencies require finer shingle particles, which increases the cost for grinding the shingles. The processing cost of PC–RAS will be greater than that of MW–RAS, since the PC–RAS tends to have more deleterious materials to remove. This cost analysis includes RAS processing and handling fees of $10 and $25 per ton. Tipping fees can range from $0 to $75 in most areas and vary considerably depending on location, availability of shin- gles, and waste disposal fees. The effect of tipping fees was evaluated at $0 and $75 per ton. Based on the aforementioned expected ranges for each factor, savings estimates for using RAS were developed. Potential savings associated with eliminating new fibers to the mixture were not included, since fibers are only used in special mix types. The results of the analysis are provided in Table 6-1 through Table 6-4. The estimated potential savings ranges from $0.81 to $12.60 per ton, with an overall average potential savings of $5.02 per ton. For the ranges of each fac- tor evaluated, the tipping fee had the greatest impact on total savings, followed by the price of virgin asphalt and then the percentage of RAS used in the mixture. It is important to note that these estimated potential sav- ings do not include costs of modifications to the asphalt plant that may be necessary to add RAP, such as an additional feeder bin and conveyors, controls modifications, drier modifica- tions, and, possibly, a RAS stockpile cover to minimize mois- ture from precipitation. Nor does it include extra costs—such as additional testing, increased virgin asphalt content, or the use of softer binders or rejuvenators—that may be incurred to design mixtures with RAS. Finally, it does not consider the impact that using RAS may have on allowable RAP content of the mixtures. The economics of using RAS is most favorable when con- tractors are able to maximize tipping fees and use higher percentages of RAS, when RAP content is not impacted, and when virgin asphalt prices are relatively high. Agencies are more likely to realize an economic benefit when competition among contractors is good and the performance of mixtures containing RAS is equal to or better than mixtures without RAS. Further studies of field projects using mixtures contain- ing RAS over at least 5 years of service are needed to prove or disprove the latter. Tipping Fee ($) RAS Processing and Handling Cost ($) Mixing Efficiency of RAS (%) RAS Asphalt Content (%) Estimated Savings per Ton ($) 0 10 75 20 1.26 75 10 75 20 3.51 0 25 75 20 0.81 75 25 75 20 3.06 0 10 100 20 1.71 75 10 100 20 3.96 0 25 100 20 1.26 75 25 100 20 3.51 0 10 75 30 1.94 75 10 75 30 4.19 0 25 75 30 1.49 75 25 75 30 3.74 0 10 100 30 2.61 75 10 100 30 4.86 0 25 100 30 2.16 75 25 100 30 4.41 Table 6-1. Cost for 3% RAS and virgin asphalt cost of $300 per ton.

Tipping Fee ($) RAS Processing and Handling Cost ($) Mixing Efficiency of RAS (%) RAS Asphalt Content (%) Estimated Savings per Ton ($) 0 10 75 20 2.61 75 10 75 20 4.86 0 25 75 20 2.16 75 25 75 20 4.41 0 10 100 20 3.51 75 10 100 20 5.76 0 25 100 20 3.06 75 25 100 20 5.31 0 10 75 30 3.96 75 10 75 30 6.21 0 25 75 30 3.51 75 25 75 30 5.76 0 10 100 30 5.31 75 10 100 30 7.56 0 25 100 30 4.86 75 25 100 30 7.11 Table 6-2. Cost for 3% RAS and virgin asphalt cost of $600 per ton. Tipping Fee ($) RAS Processing and Handling Cost ($) Mixing Efficiency of RAS (%) RAS Asphalt Content (%) Estimated Savings per Ton ($) 0 10 75 20 2.10 75 10 75 20 5.85 0 25 75 20 1.35 75 25 75 20 5.10 0 10 100 20 2.85 75 10 100 20 6.60 0 25 100 20 2.10 75 25 100 20 5.85 0 10 75 30 3.23 75 10 75 30 6.98 0 25 75 30 2.48 75 25 75 30 6.23 0 10 100 30 4.35 75 10 100 30 8.10 0 25 100 30 3.60 75 25 100 30 7.35 Table 6-3. Cost for 5% RAS and virgin asphalt cost of $300 per ton. Tipping Fee ($) RAS Processing & Handling Cost ($) Mixing Efficiency of RAS (%) RAS Asphalt Content (%) Estimated Savings per Ton ($) 0 10 75 20 4.35 75 10 75 20 8.10 0 25 75 20 3.60 75 25 75 20 7.35 0 10 100 20 5.85 75 10 100 20 9.60 0 25 100 20 5.10 75 25 100 20 8.85 0 10 75 30 6.60 75 10 75 30 10.35 0 25 75 30 5.85 75 25 75 30 9.60 0 10 100 30 8.85 75 10 100 30 12.60 0 25 100 30 8.10 75 25 100 30 11.85 Table 6-4. Cost for 5% RAS and virgin asphalt cost of $600 per ton.

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Using Recycled Asphalt Shingles with Warm Mix Asphalt Technologies Get This Book
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TRB's National Cooperative Highway Research Program (NCHRP) Research Report 890: Using Recycled Asphalt Shingles with Warm Mix Asphalt Technologies documents the development of a design and evaluation procedure that provides acceptable performance of asphalt mixtures incorporating warm mix asphalt (WMA) technologies and recycled asphalt shingles (RAS)—with and without recycled asphalt pavement (RAP)—for project-specific service conditions.

Since the introduction of the first WMA technologies in the U.S. about a decade ago, it has quickly become widely used due to reduced emissions and production costs of mixing asphalt at a lower temperature. The use of RAS has increased significantly over the past 10 years primarily due to spikes in virgin asphalt prices between 2008 and 2015. The report addresses the amount of mixing between RAS binders and virgin binders when WMA is used.

It provides additional guidance for designing, producing, and constructing asphalt mixtures that use both RAS and WMA to address several gaps in the state-of-the-knowledge on how these two technologies work, or perhaps, don’t work together.

The report also identifies ways to minimize the risk of premature failure due to designing and producing mixes containing WMA technologies and RAS with poor constructability and durability.

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