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A Manual for Design of Hot-Mix Asphalt with Commentary (2011)

Chapter: Chapter 9 - Reclaimed Asphalt Pavement

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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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Suggested Citation:"Chapter 9 - Reclaimed Asphalt Pavement." National Academies of Sciences, Engineering, and Medicine. 2011. A Manual for Design of Hot-Mix Asphalt with Commentary. Washington, DC: The National Academies Press. doi: 10.17226/14524.
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148 The asphalt paving industry is a leader in the use of recycled products. HMA pavement is the most recycled material in the world. In addition to recycled asphalt pavement (RAP), other recycled materials are routinely used in HMA mixtures including • Foundry sand • Glass • Roofing shingles • Slag • Tire rubber Recommendations for designing HMA with recycled materials other than RAP are not included in this manual. In areas where they are used, HMA producers have worked closely with agencies to modify mixture design and production methods to effectively use recycled products. Engineers and technicians considering the use of such products in HMA should obtain specific guidance from agencies with substantial experience in their use. The references at the end of this chapter include several publications addressing various recycled products used regionally in HMA. RAP, on the other hand, is a recycled product that is used extensively in HMA throughout the United States. RAP is old asphalt pavement that has been removed from a road by milling or full depth removal. With appropriate mixture design and production considerations, RAP can be reused in HMA to produce mixtures meeting normal specification requirements. The use of RAP in HMA eliminates the need to dispose of old asphalt pavements and conserves asphalt binders and aggregates. This results in significant production cost savings and benefits to society. RAP has been effectively used in HMA since the mid 1970s. Advances in HMA plants and processing equipment make it possible to consider mixtures with RAP contents of 50% or more. Experience has shown that, when properly designed and constructed, HMA mixtures with RAP will perform as well as mixtures produced from all new materials. The remainder of this chapter presents recommended methods for designing HMA mixtures with RAP. These methods are based primarily on those contained in NCHRP Report 452: Recommended Use of Reclaimed Asphalt Pavement in the Superpave Mix Design Method: Technician’s Manual. General Mixture Design Considerations for RAP The design of HMA containing RAP assumes that the mixture is produced using a process that results in complete mixing of the RAP with the new binder and aggregate. When complete mixing occurs, the total binder content of the mixture includes both the binder contained in the RAP and the amount of new binder added. In this situation, the properties of the binder in the mixture are the blended properties of the new binder and the RAP binder. Additionally, the C H A P T E R 9 Reclaimed Asphalt Pavement

gradation and other properties of the aggregates are those for the combined blend of the new and RAP aggregates. An important consideration in the production of HMA containing RAP is ensuring that adequate mixing of the new and RAP materials occurs. The design of HMA containing RAP requires substantial testing to characterize the properties of the RAP—testing that is not needed in mix designs that do not contain RAP. To effectively design and produce any mixture with RAP, the following properties of the RAP must be determined: • RAP binder content • RAP aggregate gradation • Specific gravity of the RAP aggregate • Angularity of the coarse aggregate particles in the RAP • Flat and elongated particles for the coarse aggregate in the RAP • Angularity of the fine aggregate in the RAP To determine these properties, the binder must be removed from the RAP using either an ignition oven or solvent extraction. The ignition oven is preferred when correction factors can be reasonably estimated and it is known that the properties of local aggregates are not altered substantially by exposure to the high temperatures in the ignition oven. When the RAP is limited to a low percentage of the new mixture, 15% or less (as a percentage of the aggregate blend), it is not necessary to determine the properties of the RAP binder. Small amounts of the aged RAP binder have little effect on the properties of the mixture. When higher percentages of RAP are used, the stiffness of the RAP binder must be considered. This can be done in several ways. Some agencies simply require that mixtures containing RAP use a softer binder than normally used in their region. A more precise approach involves using a blending chart or a spreadsheet to estimate the grade of the binder formed by blending the RAP binder and the new binder. When a blending chart (or an appropriately designed spreadsheet such as HMA Tools) is used, samples of the RAP binder must be obtained for testing through the use of solvent extraction and subsequent recovery of binder. The recommended blending analysis considers the high, intermediate, and low pavement temperature properties of both the RAP binder and the new binder. The objective of the analysis is to obtain a blended binder meeting the performance grade requirements for the environment where the pavement will be constructed. The range of RAP that can be feasibly added to a mixture is an important consideration in the design of HMA with RAP. The minimum RAP content depends on the capability of plant equipment to accurately and consistently add the RAP. For most plants, this amount is on the order of 10 percent. The maximum amount of RAP that can be added to a mixture depends on several factors including • Amount of RAP available • Specification limits • Capability of the hot-mix plant to dry, heat, and effectively mix the RAP material • Gradation of the RAP aggregate, particularly the amount of material passing the 0.075-mm sieve • Variability of the RAP • Properties of the RAP binder and available new binders Often the maximum RAP content is governed by the amount of material in the RAP passing the 0.075-mm sieve and the variability of the RAP. In recent years, equipment to size (or fractionate) RAP has been developed to overcome these limitations. This equipment can separate RAP into various sizes for more effective use in HMA mixtures. Sizing the RAP reduces variability in the gradation and binder content and provides the flexibility to use specific components of the available RAP in different mixtures. A consequence of this practice is that the design of mixtures Reclaimed Asphalt Pavement 149

150 A Manual for Design of Hot Mix Asphalt with Commentary incorporating RAP may require the consideration of multiple RAP stockpiles each with a specific aggregate gradation and binder content. Overview of the Mixture Design Process with RAP Figure 9-1 is a flowchart for designing HMA mixtures with RAP. In the volumetric design and performance analysis, RAP stockpiles are treated much the same as new material stockpiles. RAP stockpiles, however, require additional testing to characterize the properties and the variability of the RAP material. SAMPLE RAP STOCKPILES 8 - 10 LOCATIONS SPLIT SAMPLE FOR BINDER CONTENT AND GRADATION ANALYSIS DETERMINE AVERAGE AND STANDARD DEVIATION OF BINDER CONTENT AND GRADATION DETERMINE FEASIBLE RAP CONTENTS BASED ON GRADATION AND VARIABILITY DESIRED RAP CONTENT >15 % ? COMBINE INDIVIDUAL SAMPLES TO OBTAIN REPRESENTATIVE SAMPLE SPLIT SAMPLE FOR CHARACTERIZING RAP AGGREGATE AND BINDER PROPERTIES RAP AGGREGATE PROPERTIES RAP BINDER PROPERTIES BLENDING CHART ANALYSIS Yes VOLUMETRIC MIXTURE DESIGN PERFORMANCE TESTING AS REQUIRED No Figure 9-1. Overview of HMA mixture design with RAP.

When RAP is used in HMA, the first step in the mixture design process is to obtain samples of the RAP. Samples should be taken from random locations in each RAP pile. A portion of each sample is then used to determine the average and standard deviation of the binder content and gradation. This information is used to estimate feasible RAP contents that will satisfy gradation and vari- ability requirements. The remaining portion of the RAP samples for each stockpile are combined to provide (1) a representative sample for determining RAP binder and aggregate properties and (2) material for preparing specimens for the volumetric design and performance analysis. If the desired RAP content exceeds 15% or a limit specified by the agency, the properties of the RAP binder are analyzed and used to create a blending chart for the new and RAP binder. This blending chart can be used to determine the maximum RAP content of a specified new binder to ensure the blended binder meets the specified grade. Or it can be used to determine the grade of new binder needed for the desired RAP content to ensure that the blended binder meets the specified grade. If more than one RAP stockpile will be used in a mixture, the binder analysis is performed using a blended sample of the RAP stockpiles. The results of the variability and RAP binder analyses are used to select the final RAP content and performance grade of the new binder that will be used in the mixture. The volumetric design and performance analysis then proceed in the same manner as for a mixture produced with all new materials. The only difference is the binder content in the RAP stockpiles must be accounted for when computing binder contents and preparing specimens. A Note on General Methods of Handling RAP This manual assumes that RAP will be collected and stored in discrete stockpiles, with each stockpile representing a single RAP source or several very similar and carefully handled RAP sources. There are several good reasons for handling RAP in this way. Perhaps most impor- tantly, it ensures that each stockpile is relatively uniform in character and will not vary too much as the stockpile is depleted during production. It makes characterizing the RAP simpler and more accurate, since the variability in the RAP source is minimized. Some agencies require that RAP be handled in this way and place restrictions on the size of RAP stockpiles that can be used at HMA plants. However, there are other ways to handle RAP in HMA plants. One approach gaining popularity is to fully process the RAP—to sieve and blend it into carefully controlled size fractions which are then stored and handled in much the same way as aggregates. This approach has many advantages, but because it is relatively new it is not directly addressed in this manual. Many aspects of the mix design process, such as determining binder grades for mix designs containing RAP, will be essentially the same regardless of how the RAP is handled. One important aspect of the mix design process that will depend on how RAP materials are handled at the plant is the effect of RAP variability on the allowable RAP content. Producers using highly processed RAP and other alternative approaches to handling RAP should rely on their experience and judgment in determining the maximum amount of RAP that can be used in HMA mix designs without unacceptably increasing production variability. Using HMA Tools to Design HMA Mixes with RAP Many of the equations used in the design of HMA mixes containing RAP are complex, and the calculations required to properly complete such designs can be tedious and prone to error. The HMA Tools spreadsheet has been constructed to simplify the incorporation of RAP into dense-graded HMA mix designs. Technicians and engineers need not be overly concerned with the mathematics involved in incorporating RAP into HMA mix designs, but technicians and engineers Reclaimed Asphalt Pavement 151

should understand the principles involved. The information in this chapter, therefore, focuses on these principles—not the mathematical details. Readers interested in the technical details underlying the information in this chapter should refer to the Commentary on the HMA Mix Design Manual. Frequent reference is also made to how the HMA Tools spreadsheet is used in the mix design process; the examples have been constructed around HMA Tools. In compiling this chapter, it is assumed that the reader has reviewed Chapter 8 on dense-graded HMA mix designs and understands both the concepts involved in the mix design process and the use of most of the functions in the HMA Tools spreadsheet. Readers unfamiliar with either of these topics should take the time to review Chapter 8. RAP Sampling Samples of RAP can be obtained from several locations, including the roadway by coring, trucks hauling milled material for stockpiling, stockpiles prior to processing, and stockpiles after processing. Milling and processing operations break down some of the aggregate in the RAP, producing finer gradations with increased percentages passing the 0.075-mm (#200) sieve. Since a representative sample of RAP will be used directly in the mixture design process, it is critical that RAP samples obtained for HMA mixture design be representative of the RAP that will be used in the mixture. For this reason, the location recommended for sampling RAP is from stockpiles of the RAP after final processing. Sampling RAP from a stockpile is similar to sampling aggregate from a stockpile, except crusts form on RAP stockpiles that must be removed before samples can be taken. General guidance for stockpile sampling is provided in AASHTO T 2. As discussed in AASHTO T 2, segregation is a major concern when sampling from stockpiles. The preferred approach for stockpile sampling is to use a loader or other power equipment to obtain smaller sampling piles from selected locations within the main stockpile. The RAP sample for each location is then taken from the smaller sampling pile. RAP stockpiles should be sampled from at least five locations distributed throughout the pile. A larger number of samples—up to 20 or more—is desirable, since this will allow a more accurate characterization of the RAP and permit the highest possible RAP content in the final mix design(s). The sample size depends on the number of mixture designs that will be developed using the RAP in the stockpile. At each sampling location, obtain 10 kg (22 lb) of RAP for each mixture design that will be prepared, plus 5 kg (11 lb) for characterization of the RAP. For example, if three mixtures (a base, intermediate, and surface) will be designed using the same RAP, then obtain 35 kg (77 lb) of RAP at each sampling location. This sample size will provide sufficient material to characterize the properties and variability of the RAP stockpile and provide a rep- resentative sample for use in mixture design. There are two objectives for the RAP sampling. The first is to determine the average and vari- ability (in terms of standard deviation) of the binder content and aggregate gradation in the RAP in the stockpile. For this analysis, a 5 kg (11 lb) sub-sample should be split from the sample taken at each stockpile location using the methods described in AASHTO T 248. This sub-sample will then be tested to determine the average and standard deviation of the binder content and aggre- gate gradation within the RAP stockpile. As discussed in the next section, variability is an impor- tant consideration in the selection of feasible RAP contents that can be considered in design. The second objective of the sampling is to obtain representative materials for the mixture design. A representative sample is formed by combining the remaining portion of the samples from each sampling location. From this representative RAP sample, aggregate properties and, if required, binder properties will be determined and specimens for volumetric and performance analysis 152 A Manual for Design of Hot Mix Asphalt with Commentary

Reclaimed Asphalt Pavement 153 prepared. Figure 9-2 is a general flowchart for sampling a RAP stockpile for use in HMA mix- ture design. Blending and Variability RAP variability is an important consideration in the design of HMA incorporating RAP. Many agency specifications require mixtures with RAP to be produced to the same production tolerances as mixtures made with all new materials. If highly variable RAP is used, then the HMA may not meet production tolerances, resulting in lost production time, a penalty, or, in extreme cases, the need to remove and replace the mixture. The amount of RAP that can be added without exceeding OBTAIN STOCKPILE SAMPLES AASHTO T2 Size = 10 kg x (number of mix designs) + 5 kg SELECT 8 -10 RANDOM SAMPLING LOCATIONS BINDER CONTENT AND GRADATION FOR BLENDING AND VARIABILITY ANALYSIS CHARACTERIZE RAP AGGREGATE PROPERTIES VOLUMETRIC MIXTURE DESIGN AND PERFORMANCE ANALYSIS CHARACTERIZE RAP BINDER PROPERTIES IF REQUIRED SPLIT SAMPLE AASHTO T248 SPLIT SAMPLE AASHTO T248 5 kg COMBINE WITH OTHER LOCATIONS TO CREATE REPRESENTATIVE SAMPLE REMAINDER 2.5 kg COMBINE WITH OTHER LOCATIONS TO CREATE REPRESENTATIVE SAMPLE 2.5 kg SPLIT SAMPLE AASHTO T248 2.5 kg REMAINDER Figure 9-2. Flow chart for recommended sampling of RAP stockpiles.

specification limits depends on the limits themselves, the variability of the RAP, the variability of similar mixtures produced without RAP, and the consistency of the equipment adding the RAP. Unfortunately, the calculation of maximum RAP content based on a variability analysis is quite complicated and often some of the information required is uncertain or even unknown. For these reasons, the approach recommended in this manual is somewhat simplified, but based soundly on the basic statistical theory involved. It will provide engineers and technicians with reasonable estimates of the amount of RAP that can be incorporated into a mix design without unaccept- able increases in production variability. Two different methods can be used to determine the maximum allowable RAP content based on variability: a graphical approach and the HMA Tools spreadsheet. The same statistics are used in both cases, but HMA Tools is a more precise approach that will often allow for somewhat higher RAP contents. Because many state highway agencies already have specifications in place establishing allow- able RAP contents in HMA mixtures, HMA Tools allows any RAP content in the design process. If desired, HMA Tools can be used to perform the statistical analysis of RAP stockpiles and to determine the maximum allowable RAP content. However, this is not required. Thus, the user can enter any desired RAP content when using HMA Tools to develop mix designs. RAP Binder Content and Aggregate Gradation: Laboratory Procedures The average and standard deviation of the binder content and aggregate gradation in the RAP stockpiles are properties that must be measured to effectively design HMA with RAP. The 5 kg sub-samples split from the sample taken at each sampling location are used for this analysis. If reasonable estimates of the ignition oven correction factors for local aggregates can be made, then the RAP binder content can be determined using an ignition oven, AASHTO T 308. The gradation of the RAP aggregates is then determined using AASHTO T 30 after application of the aggregate correction factors as described in AASHTO T 308. If correction factors for local aggregates are unknown or highly variable, then the RAP binder content must be determined by solvent extraction, AASHTO T 164. The gradation of the extracted aggregate is then determined using AASHTO T 30. If desired, ignition oven correction factors can be established by performing both analyses on split samples from at least three locations in the stockpile. Determining Combined Gradation and Binder Content The computation of blends for mixtures incorporating RAP is a little different than that for mixtures made with all new stockpiles. When RAP is used, the RAP material that is added includes both the RAP aggregate and the RAP binder. Since gradation data are based on the weight of aggregate, and binder contents are based on the total weight, the stockpile percentages must be adjusted for combined gradation analysis based on the amount of binder contained in the RAP. In using HMA Tools to determine the composition of HMA mixes containing RAP, data on the aggregate gradations—including the gradation of aggregate contained in the RAP— is entered in the worksheet “RAP_Aggregates.” Aggregate bulk and apparent specific gravity data is also entered here, along with the asphalt binder content and specific gravity. Data for up to four RAP stockpiles can be entered. General information for the mix—most importantly the tar- get VMA and air void content—are entered in the worksheet “General.” The actual composition of the blend is entered in the worksheet “Trial_Blends,” which then lists the combined gradation and various other data for the mix. The example below illustrates the use of HMA Tools in cal- culating the composition of an HMA mixture containing RAP. 154 A Manual for Design of Hot Mix Asphalt with Commentary

Reclaimed Asphalt Pavement 155 Example Problem 9-1. Gradation and Binder Content Analysis for an HMA Mixture Containing RAP A 9.5-mm NMAS mixture will be produced using three new aggregate stockpiles, hydrated lime, and two RAP stockpiles. Gradation and binder content data for each stockpile is given in Table 9-1. The stockpiles will be combined in the follow- ing proportions: 29% of Aggregate 1, 40% of Aggregate 2, 10% of Aggregate 3, 1% lime, 10% Coarse RAP, and 10% Fine RAP. The target VMA should be 16.0% and the target air void content 4.0%. The specific gravity value for both the new binder and the RAP binders is 1.030. For this combination of stockpiles, compute the combined gradation, the binder provided by the RAP, and the amount of new binder required. Solution The general mix information is entered in the worksheet “General”; this must include the target VMA of 16% and the target air void content of 4%. The gradation informa- tion and specific gravity values for the aggregates are entered in the worksheet “Aggregates” and for the RAP in the worksheet “RAP_Aggregates.” Asphalt binder con- tent and other information for the RAP is also entered in this worksheet. The composition of the blend, that is, the weight percentage of each aggregate and the RAP materials, is entered in the worksheet “Trial_Blends” as Trial No. 1. Make sure to enter the target VMA and tar- get air void content in this worksheet. The total binder content for the mix is given in cell F43 as 5.46%. Of this amount, 0.75% is from the RAP (cell F143) and 4.72% from the new binder (cell F145). The combined gradation for this example problem is given in Table 9-2. Property Sieve Size, mm Agg. 1 Agg. 2 Agg. 3 Hydrated Lime Coarse RAP Fine RAP 19.0 100 100 100 100 100 100 12.5 100 100 100 100 100 100 9.5 91 100 100 100 94 100 4.75 19 98 90 100 34 91 2.36 6 61 52 100 25 65 1.18 5 37 31 100 22 46 0.600 4 24 20 100 20 34 0.300 4 16 14 100 16 25 0.150 3 8 10 96 12 19 Gradation, % Passing 0.075 2.9 3.6 8.4 89 10.4 15.7 Agg. Bulk Spec. Grav. 2.610 2.627 2.619 2.602 2.624 2.614 Agg. App. Spec. Grav. 2.628 2.651 2.645 2.675 2.638 2.637 Binder Content, % --- --- --- --- 3.1 4.5 Table 9-1. Stockpile materials for example 1. Sieve Size, mm Percent Passing 19 100 12.5 100 9.5 97 4.75 67 2.36 41 1.18 27 0.60 19 0.30 14 0.15 9 0.075 6.6 Table 9-2. Combined gradation for the proposed HMA mixture for example 1.

Limiting Variability in HMA Mixes Containing RAP Because the variability of the RAP properties in a given stockpile can be quite large, it is important to estimate this variability and make sure that the addition of the RAP to an HMA mixture will not cause unacceptable increases in production variability. Controlling variability in mixes containing RAP involves three steps: 1. Sampling RAP stockpiles, as described previously. 2. Calculating the standard deviation for aggregate percent passing and binder content for all RAP stockpiles. 3. Estimating the maximum amount of RAP that can be added to the mix without exceeding allowable production variability. The variability of a mixture of several components, such as HMA, depends on the variability of the components, the proportions of the components, the precision of the blending, and the mean value of the components. Calculation of the standard deviation for aggregate gradations (percent passing) and asphalt content for HMA containing RAP can be quite complicated; as with other aspects of developing RAP mix designs, the details are not presented here but are included in the Commentary. The mean and standard deviation values for aggregate gradation and asphalt binder content are calculated in HMA Tools in the worksheet “RAP_Variability.” Data for aggre- gate gradation and binder content are entered here for up to four RAP stockpiles. Data for up to 30 specimens can be entered for each of these four stockpiles. If no more than 15% RAP is to be used in a mix design, there is no need to perform a variability analysis of the RAP stockpiles used in the mix design. The standard deviation values calculated in the worksheet “RAP_Variability” are only esti- mates of the true values. There is a 50% chance that the true standard deviation for a given RAP stockpile will be higher than the calculated value. There is a relatively small chance that the true standard deviation will be much, much higher than the estimated value. Because the standard deviation values calculated for the RAP stockpiles are only estimates, the values used by HMA Tools in determining the maximum allowable RAP content is an upper confidence limit, rather than the calculated value. In cell B6, the reliability (confidence) level for this esti- mate is entered; a value of 80% is suggested. The more samples used in calculating the stan- dard deviation, the more accurate the estimate will be and the lower the value of upper confi- dence limit for the standard deviation. Therefore, it is suggested that at least five samples be used for calculating the mean and standard deviation for a RAP stockpile. Larger numbers of samples—up to 30—will provide greater accuracy and will normally allow greater percentages of RAP to be used in the mix design. In using HMA Tools to perform a variability analysis of RAP stockpiles, gradation data for up to 30 samples for the first RAP stockpile are entered in cells B19:AE31; asphalt content is entered in cells B33:AE33. Gradation data for up to three more RAP stockpiles are entered in cell ranges immediately below this. The approximate proportions to which the stockpiles will be blended must be entered in cells B9:B12. The estimated maximum allowable RAP content will appear in cell B14 when data entry is complete and the calculation is completed. Because up to 15% RAP can be used in any HMA design without performing a variability analysis, the maximum allowable RAP content will never go below 15%. Similarly, since handling large amounts of RAP during HMA production is often difficult for practical reasons, HMA Tools limits the maximum allowable RAP to 50%. If needed, the average percent passing and stan- dard deviation for percent passing for the first RAP stockpile can be read in cells AH19:AH31 and AI19:AI31, respectively. The average and standard deviation of the asphalt binder content 156 A Manual for Design of Hot Mix Asphalt with Commentary

Example Problem 9-2. Calculation of Mean, Standard Deviation, and Maximum Allowable RAP Content for a Single RAP Stockpile A 30,000-ton RAP stockpile was constructed using millings from several projects. Table 9-3 summarizes the results of binder content and gradation tests on 10 ran- dom samples from the stockpile. Calculate the mean, the standard deviation, and the 80% upper confidence limit of the standard deviation for percent passing. Also, using HMA Tools determine the maximum allowable RAP content for this RAP stockpile. Solution The values for percent passing and asphalt binder content given in Table 9-3 are entered in cells B19:K31 and B33:K33 in the worksheet “RAP_Variability.” The reliability level in cell B6 should be the default value of 80%. Only one RAP stock- pile is being used, so 100 is entered in cell B9, and cells B10:B12 are left blank. After calculation (press F9 to make sure HMA_Tools performs the needed calcula- tions), the mean values are given in cells AH19:AH31 and AH33, the standard deviation values are given in cells AI19:AI31 and AI33, and the values for the upper confidence limit for standard deviation are given in cells AJ19:AJ31 and AJ33. Values for average, standard deviation, and the upper confidence limit for standard deviation are listed in Table 9-4. The maximum allowable RAP content of 42% appears in cell B19. Sample Number Property Sieve Size, mm 1 2 3 4 5 6 7 8 9 10 19.0 100 100 100 100 100 100 100 100 100 100 12.5 98 100 100 99 99 100 100 100 98 98 9.5 91 98 100 94 97 97 95 93 94 94 4.75 67 77 75 71 73 78 75 69 70 72 2.36 53 59 55 54 58 59 57 50 52 53 1.18 39 44 48 43 49 46 45 41 39 41 0.600 32 38 37 35 39 36 37 33 32 33 0.300 22 27 25 23 26 23 25 21 22 22 0.150 14 17 16 15 16 14 15 14 13 15 Gradation, % Passing 0.075 10.7 12.2 11.9 10.7 12.9 10.3 11.9 10.5 9.8 10.8 Asphalt Content, % 4.0 4.5 4.7 4.4 5.1 4.6 4.6 4.3 4.6 4.8 Property Sieve Size, mm Average Standard Deviation Upper Confidence Limit for Std. Dev. 19.0 100.9 0.00 0.00 12.5 99.2 0.92 1.19 9.5 95.3 2.67 3.45 4.75 72.7 3.56 4.61 2.36 55.0 3.13 4.04 1.18 43.5 3.54 4.57 0.600 35.2 2.57 3.33 0.300 23.6 2.01 2.60 0.150 14.9 1.20 1.55 Gradation, % Passing: 0.075 11.2 0.99 1.28 Asphalt Binder Content, Wt. % --- 4.56 0.295 0.382 Table 9-3. Results of binder content and gradation tests on RAP stockpile for example 2. Table 9-4. Computed averages and standard deviations for the RAP stockpile for example 2.

appear in cells AH33 and AI33, respectively. The average and standard deviation of the per- cent passing and binder content for up to three additional RAP stockpiles appear immediately below these cells. Determining Maximum Allowable RAP Content Based on Variability Using a Graphical Approach Instead of using HMA Tools, a graphical approach can be used to determine the maximum allowable RAP content in an HMA mix design. Figures 9-3 through 9-6 are design charts for estimating the maximum allowable RAP content for an HMA mix design, based on the vari- ability in gradation and asphalt binder content of the RAP. Figure 9-3 gives the maximum RAP content based on the standard deviation for aggregate percent passing for a single RAP stock- pile. Figure 9-4 gives estimated maximum RAP content based on the standard deviation for asphalt binder content for a single RAP stockpile. Figure 9-5 gives estimated maximum RAP content based on the average standard deviation for aggregate percent passing for a blend of RAP stockpiles, while Figure 9-6 gives estimated maximum RAP content based on the average 158 A Manual for Design of Hot Mix Asphalt with Commentary 15 20 25 30 35 40 45 50 0 1 2 3 4 5 6 7 8 9 10 Standard Deviation for RAP Aggregate % Passing M ax . R A P Co nt en t, W t. % Sieve size, mm: 0.075 0.150 0.300 1.18 4.75 > 9.5 & 0.600 & 2.36 & 9.5 15 20 25 30 35 40 45 50 0.2 0.3 0.4 0.5 0.6 0.7 Binder Standard Deviation M ax . R A P Co n te n t, W t. % Figure 9-3. Maximum RAP content as a function of standard deviation for aggregate percent passing. For n = 5 Samples from a single RAP stockpile. Figure 9-4. Maximum RAP content as a function of standard deviation for asphalt binder content. For n = 5 Samples from a single RAP stockpile.

standard deviation for asphalt binder content for a blend of RAP stockpiles. Figures 9-5 and 9-6 are different from 9-3 and 9-4 because, when several RAP stockpiles are blended, the variabil- ity in the resulting blend will tend to be significantly lower than the variability in the individ- ual stockpiles. Figures 9-5 and 9-6 are based on the assumption that no RAP stockpile in the RAP blend will make up more than 70% of the RAP blend; if this assumption is not correct, Fig- ures 9-3 and 9-4 should be used with the standard deviation values for the stockpile making up most of the RAP blend. All four charts are based on statistics calculated from five independent samples; they cannot be used for smaller sample sizes. These charts can be used for statistics cal- culated using more than five samples, but doing so will tend to underestimate the amount of RAP that can be used in the mix design. To use these charts, the maximum allowable RAP must be determined for each sieve size for which the percent passing is less than 100%. The maximum allowable RAP must also be determined for the asphalt binder content. The maximum allowable RAP content is then the lowest of all these individual values. The procedure is probably best illustrated with an example problem. Reclaimed Asphalt Pavement 159 15 20 25 30 35 40 45 50 M a x . R A P Co n te n t, W t. % 0 1 2 3 4 5 6 7 8 9 10 Average Standard Deviation for RAP Aggregate % Passing Sieve size, mm: 0.075 0.150 0.300 1.18 4.75 > 9.5 & 0.600 & 2.36 & 9.5 15 20 25 30 35 40 45 50 Average Binder Standard Deviation M ax . R A P Co nt en t, W t. % 0.2 0.3 0.4 0.5 0.6 0.7 Figure 9-5. Maximum RAP content as a function of average standard deviation for aggregate percent passing. For n = 5 Samples from a blend of RAP stockpiles, and no stockpile making up more than 70% of the RAP blend. Figure 9-6. Maximum RAP content as a function of average standard deviation for asphalt binder content. For n = 5 Samples from a blend of RAP stockpiles, and no stockpile making up more than 70% of the RAP blend.

Maximum RAP Content, Variability and Binder Properties The methods described above for estimating maximum allowable RAP content are based only on variability analysis—the maximum values for RAP content determined in this way only provide an estimate of how much RAP can be used in a mix design without significantly increasing production variability. These maximum values do not address the equally important issue of how the RAP content will affect the final binder grade in the HMA mix. The asphalt binder contained 160 A Manual for Design of Hot Mix Asphalt with Commentary Example Problem 9-3. Determination of Maximum Allowable RAP Content Based on Variability Analysis Using the Graphical Approach Using the standard deviation values for aggregate percent passing and asphalt binder content calculated for Example 2, estimate the maximum allowable RAP content based on variability using Figures 9-3 and 9-4. Solution Table 9-5 lists the average percent passing and standard deviation for percent pass- ing for the RAP stockpile first introduced in Example 2. This also shows the average and standard deviation for asphalt binder content. The last column in Table 9-5 shows the maximum allowable RAP content based on variability for each individual sieve and asphalt binder content, as determined using Figures 9-3 and 9-4. The val- ues range from 30 to 50%; the lowest value is 30% (for the 1.18-mm sieve and the asphalt binder content); therefore, the overall maximum allowable RAP content based on variability is 30%. Note that this percentage is significantly less than the 42% found in Example 2 for the same standard deviation values. The value deter- mined using the graphical approach is lower because it is based on a sample size of n = 5. As mentioned above, using Figures 9-3 through 9-6 for cases where samples sizes larger than 5 are used to calculate standard deviation values will provide lower estimates of maximum allowable RAP content than would be found using more accurate methods such as the HMA Tools spreadsheet. Property Sieve Size, mm Average Standard Deviation Maximum Allowable RAP Content % 19.0 100.9 0.00 50 12.5 99.2 0.92 50 9.5 95.3 2.67 50 4.75 72.7 3.56 40 2.36 55.0 3.13 38 1.18 43.5 3.54 30 0.600 35.2 2.57 38 0.300 23.6 2.01 50 0.150 14.9 1.20 50 Gradation, % Passing: 0.075 11.2 0.99 50 Asphalt Binder Content, Wt. % --- 4.56 0.295 30 Maximum Allowable RAP Content for Stockpile: 30 Table 9-5. Standard deviation values and estimated maximum allowable RAP content for example 3.

in RAP is likely much harder than new asphalt binders used in HMA mix designs and, when significant amounts of RAP are added to a mix, the binder from the RAP will blend with the new asphalt binder added to the mix to produce a blended binder that can be substantially harder than the new binder added to the HMA mixture. For this reason, the amount of RAP that can be added to a mixture can be limited not only by variability, but also by the blended binder grade. The issue of determining blended binder grades in HMA mix designs containing RAP is discussed later in this chapter. RAP Aggregate Properties In addition to gradation, bulk specific gravity, angularity, and particle shape are properties of the RAP aggregate that are needed to effectively design HMA with RAP. These properties are measured on a representative sample of the RAP stockpile that is formed by combining samples from each of the stockpile locations. Some tests must be performed on bare aggregate after removing the binder from the RAP. When experience with local aggregates indicates that they are not substantially altered by exposure to the high temperature in the ignition oven, AASHTO T 308 is the preferred method for removing the binder from the RAP aggregate for testing. Otherwise solvent extraction, AASHTO T 164, must be used. If the ignition oven is used, the aggregates must be cooled to room temperature before further handling and testing. If solvent extraction is used, the aggregates must be thoroughly dried in an oven and cooled to room temperature before further handling and testing. When the ignition oven is used, some aggregates may exhibit significant breakdown as a result of the high temperatures used in this procedure; this breakdown can alter the resulting gradation. The representative sample should be large enough to provide sufficient material for all of the tests being performed; Table 9-6 lists the required sample sizes for laboratory tests normally performed on RAP aggregate. If the nominal maximum aggregate size in the RAP is 12.5 mm or less, a 4 kg sample will be sufficient. If the nominal maximum aggregate size in the RAP is 19.0 mm or more, a 10 kg sample will be required. RAP Aggregate Bulk Specific Gravity The bulk specific gravity of each aggregate stockpile used in an HMA mixture is needed for the computation of the voids in the mineral aggregate (VMA). Two methods can be used to determine the bulk specific gravity of the RAP aggregate. The first is to estimate the bulk specific gravity of the RAP aggregate from the RAP binder content, the maximum specific gravity of the RAP, and estimates of the binder absorption in the RAP and the specific gravity of the RAP binder. The second is to measure the bulk specific gravity of the coarse and fine fraction of the Reclaimed Asphalt Pavement 161 Sample Size, kg Property Method Fraction 12.5-mm NMAS 19.0-mm NMAS Specific Gravity of Coarse Aggregate AASHTO T 85 +2.36 mm 2 3 Specific Gravity of Fine Aggregate AASHTO T 84 -2.36 mm 1 1 Coarse Aggregate Fractured Faces ASTM D 5821 +4.75 mm 0.5 1.5 Fine Aggregate Angularity AASHTO T 304 Method A -2.36 mm 0.5 0.5 Flat and Elongated Particles ASTM D 4791 +4.75 mm 2 5 Table 9-6. Sample size for RAP aggregate tests.

RAP aggregate after removing the binder with the ignition oven or solvent extraction. Details of these approaches are discussed below. Estimating RAP Aggregate Bulk Specific Gravity In this approach, the maximum specific gravity of the RAP is measured in accordance with AASHTO T 209. The maximum specific gravity is measured on a sample split from the repre- sentative sample formed for the RAP aggregate and binder analysis. The measured maximum specific gravity, the average RAP binder content from the variability analysis, and an estimate of the RAP binder specific gravity are then used to calculate the effective specific gravity of the RAP aggregate using Equation 9-1. where Gse = effective specific gravity of the RAP aggregate Gmm = maximum specific gravity of the RAP measured by AASHTO T 209 Pb = RAP binder content, wt % Gb = estimated specific gravity of the RAP binder The bulk specific gravity of the RAP aggregate can then be estimated from Equation 9-2, which is a rearranged version of the equation used in volumetric analysis to compute asphalt absorption. where Gsb = estimated bulk specific gravity of the RAP aggregate Gse = effective specific gravity of the RAP aggregate from Equation 9-1 Pba = estimated binder absorption for the RAP, wt % of aggregate Gb = estimated specific gravity of the RAP binder The overall error associated with this analysis is difficult to quantify. It depends on (1) the precision of the maximum specific gravity measurement and (2) the accuracy of the RAP binder content measurement and the estimated RAP binder absorption and specific gravity. As shown in the analysis below, the accuracy of the RAP binder content in turn depends on the accuracy of the correction factor used to analyze the ignition oven data. The single-operator precision of the maximum specific gravity test, AASHTO T 209, is 0.011 when the dry-back procedure is not required and 0.018 when it is. These are somewhat better than the single-operator precision of the aggregate bulk specific gravity tests which are 0.032 for fine aggregate (AASHTO T 84) and 0.025 for coarse aggregate (AASHTO T 85). The potential error associated with estimating the specific gravity of the RAP binder is small. For a typical mixture it is only ± 0.002 for a ±0.010 error in the bulk specific gravity of the binder. Potential errors associated with errors in the RAP binder content or the RAP binder absorption are signifi- cantly larger. These errors are shown in Figure 9-7 for RAP having a maximum specific gravity of 2.500, a total binder content of 4%, and binder absorption of 0.5%. In this case, underestimating the absorbed binder by 0.3% results in an overestimation of the bulk specific gravity of the RAP G G P G G sb se ba se b = × ⎛⎝⎜ ⎞⎠⎟ +100 1 9 2( )- G P G P G se b mm b b = −( ) − ⎛⎝⎜ ⎞⎠⎟ 100 100 9 1( )- 162 A Manual for Design of Hot Mix Asphalt with Commentary

aggregate of 0.020. Underestimating the total binder content of the RAP by 0.5% results in an underestimation of the bulk specific gravity of the RAP aggregate of 0.021. Thus the accuracy of estimating the RAP aggregate specific gravity from the maximum specific gravity and binder content of the RAP depends mostly on the accuracy of the estimated correction factor used to determine binder content with the ignition oven and the accuracy of the assumed binder absorption. The correction factor for the ignition oven should not be in error by more than 0.3% and the assumed binder content should not be in error by more than 0.2% to obtain estimated RAP aggregate specific gravity values with an accuracy similar to those measured in AASHTO T 84 and T 85. As discussed earlier, correction factors for the ignition oven can be established by performing both the ignition oven and solvent extraction analyses on split samples from at least three locations in the RAP stockpile. Measuring RAP Aggregate Specific Gravity If a reasonable estimate of the binder absorption for the RAP is not available, the specific gravity of the RAP aggregate can be measured after removing the RAP binder using an ignition oven or solvent extraction. The specific gravities of the coarse and fine fractions of the RAP aggregate are measured in accordance with AASHTO T 85 and AASHTO T 84, respectively. HMA Tools and RAP Aggregate Specific Gravity HMA Tools is designed so that either approach discussed above can be used to estimate RAP aggregate specific gravity values. If the specific gravity values are to be estimated from maximum theoretical specific gravity, binder content, and related information, the data are entered in cells C6:F9 in the worksheet “RAP_Aggregates.” If actual measured values for RAP aggregate specific gravity are used, these are entered in cells C11:F14. The calculated values for bulk and apparent specific gravity for each of up to four RAP stockpiles then appear in cells C16:F17. If data for both Reclaimed Asphalt Pavement 163 -0.040 -0.030 -0.020 -0.010 0.000 0.010 0.020 0.030 0.040 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 ERROR IN RAP BINDER CONTENT OR ABSORPTION, % ER R O R IN B UL K SP EC IF IC G RA VI TY O F R A P A G G RE G AT E RAP Binder Content RAP Binder Absorption Figure 9-7. Potential errors in bulk specific gravity of the RAP aggregate for errors in RAP binder content and binder absorption.

methods are entered in the worksheet, HMA Tools will use the measured aggregate specific gravity values in estimating the RAP specific gravity values. The estimated water absorption for each RAP stockpile appears in cells C18:F18. RAP Aggregate Specification Properties The specification properties for the RAP aggregates are determined in the same manner as for new aggregates, except that the sand equivalent test, AASHTO T 176, is not performed. The sand equivalent test measures the amount of fine clay particles contained in the aggre- gate. It is an indicator of how well binder will coat the fine aggregate. This test is not needed for RAP material because the RAP aggregate is already coated with binder. Additionally, some of the fine aggregate is lost when the ignition oven or solvent extraction is used to remove the RAP binder. The coarse fraction of the RAP aggregate is tested for fractured faces (“crush count”) in accor- dance with ASTM D 5821 and flat and elongated particles in accordance with ASTM D 4791. The fine fraction is tested for angularity in accordance with Method A of AASHTO T 304. Remember that the aggregate consensus properties apply to the blend of all aggregates in the mixture and not the individual stockpiles. Specification properties for the coarse aggregate blend can be computed from stockpile properties based on the proportion of each stockpile used in the HMA. The fine aggregate angularities of the stockpiles can be used to estimate the fine aggregate angularity of the blend. However, because different particle shapes may pack differently when combined, the fine aggregate angularity test, Method A of AASHTO T 304, should be conducted on the final blend of fine aggregates used in the mixture—both from RAP stockpiles and the new fine aggregates used in the mix design. When using HMA Tools to perform a mix design, coarse aggregate specification properties are input in cells C20:F24 of the worksheet “RAP_Aggregates.” The data for fractured faces and flat and elongated particles are entered in this range. Up to two user-defined aggregate specification properties can also be entered at the bottom of this cell range. Fine aggregate angularity values for RAP materials are entered in cells C26:F26 of the worksheet “RAP_ Aggregates.” As with the coarse aggregate fraction of the RAP, up to two user-defined fine aggregate specification properties can be entered in cells C28:F29. HMA Tools will use values entered in this worksheet to estimate specification properties for the final aggregate blend. These values appear in the worksheet “Trial_Blends” and are also given in the worksheet “Report.” RAP Binder Properties When the RAP is limited to a low percentage of the new mixture, 15% or less, it is not necessary to determine the properties of the RAP binder. Small amounts of the aged RAP binder have little effect on the properties of the mixture. When higher percentages of RAP are used, the properties of the RAP binder must be considered through the use of blending charts as described in this section. Some agency specifications adjust the new binder grade to account for the presence of RAP. These adjustments are based on analyses similar to those presented in this section using typical properties of local RAP binders and available new binders. Extraction and Recovery to Determine RAP Binder Properties To determine the RAP binder properties, the binder from the RAP must be extracted by sol- vent extraction, then recovered from the solvent. Historically AASHTO T 164 has been used 164 A Manual for Design of Hot Mix Asphalt with Commentary

for solvent extraction and the Abson recovery method, AASHTO T 170, has been used to recover the binder for testing. There is general consensus among asphalt technologists that this combination of tests alters the properties of the recovered binder. During the Strategic High- way Research Program (SHRP), a new method for extracting and recovering binders that does not alter the properties of the recovered binder was developed. This method has been stan- dardized as AASHTO T 319 and is the extraction and recovery method recommended for RAP binder analysis. When using AASHTO T 319 to extract and recover RAP binder for testing, it is extremely important to have the appropriate sample size. At least 50 g of recovered RAP binder are needed to perform the testing required to develop a blending chart. AASHTO T 319 becomes inefficient if the amount of binder recovered exceeds 60 g. Fortunately, the binder content of the RAP was determined from the stockpile variability analysis, and this binder content can be used to deter- mine the size of the sample needed for extraction and recovery. Table 9-7 lists recommended RAP sample sizes based on the binder content of RAP. This table is based on a target of 55 g of recovered binder. Recovered RAP Binder Testing Figure 9-8 is a flowchart of the RAP binder testing required to prepare a blending chart for a specific RAP binder. These are the same tests used for the performance grading of asphalt binders Reclaimed Asphalt Pavement 165 RAP Binder Content, % Recommended Sample Size, g 3.0 1833 3.2 1719 3.4 1618 3.6 1528 3.8 1447 4.0 1375 4.2 1310 4.4 1250 4.6 1196 4.8 1146 5.0 1100 5.2 1058 5.4 1019 5.6 982 5.8 948 6.0 917 Table 9-7. Recommended sample size for RAP binder extraction and recovery. EXTRACT AND RECOVER 50 to 60 g of RAP BINDER AASHTO T319 DETERMINE AS-RECOVERED HIGH TEMPERATURE TC AASHTO T315 CONDITION 35 g OF BINDER IN ROLLING THIN FILM OVEN TEST (RTFOT) AASHTO T240 DETERMINE RTFOT HIGH TEMPERATURE TC AASHTO T315 DETERMINE RTFOT INTERMEDIATE TEMPERATURE TC AASHTO T315 DETERMINE RTFOT LOW TEMPERATURE TC FOR STIFFNESS AASHTO T313 DETERMINE RTFOT LOW TEMPERATURE TC FOR m-VALUE AASHTO T313 Figure 9-8. Flowchart for RAP binder testing.

as discussed in Chapter 3. Laboratories equipped for performance grading of asphalt binders can perform the testing required to characterize RAP binders for blending chart analysis. The RAP binder testing involves determining the critical high, intermediate, and low pave- ment temperatures, TC, for the recovered RAP binder. The critical temperature is the temper- ature where the properties of the RAP binder meet the specification requirements contained in the performance graded binder specification, AASHTO M 320. These requirements are summarized in Table 9-8. For high and low pavement temperature conditions, two criteria must be considered. The critical temperature for the high pavement temperature condition is the lower of the two, while that for the low pavement temperature condition is the higher of the two. This testing, also known as determining the “true” or “continuous” grade of the binder, is performed in the same manner as grading a new binder, except the intermediate and low tem- perature properties are measured on residue from the rolling thin film oven test (RTFOT), AASHTO T 240, instead of residue from the pressure aging vessel (PAV), AASHTO R 28. Research conducted in NCHRP Project 9-12 concluded that the AASHTO M 320 properties of a blend of RAP and new binder could be accurately estimated from the as-recovered and RTFOT aged RAP binder without the need for performing PAV aging of the recovered RAP binder. This finding significantly reduces the testing time and the amount of recovered binder needed for the testing. Using HMA Tools to Grade Asphalt Binders Recovered From RAP The calculations involved in grading binders recovered from RAP materials can be tedious to apply and are not included in this manual. The interested reader can find a detailed procedure for performing these and related calculations in Appendix A of AASHTO M 323. HMA Tools can be used not only as an aid in grading RAP binders, but also in performing all binder grade calculations typically needed when designing HMA mixtures containing RAP. To use HMA Tools to perform grading calculations for binders recovered from RAP, binder test data are entered in the worksheet “RAP_Binders.” The final binder grades are given in cells D73, H73, L73, and P73 for each of up to four RAP stockpiles. The continuous grade for high, intermediate, and low temperatures are given immediately below in cells D75:D77, H75:H77, L75:L77 and P75:P77. Because continuous grading information is needed for new binders used in a RAP mix design in order to determine the grade of the blended binder in the HMA mixture, grading data for new binders must also be entered in HMA Tools when RAP designs are being prepared (unless no more than 15% RAP is being used, in which case binder grading information is not required). Binder grading data for new binders used in a mix design are entered in the worksheet “Binders.” As with the worksheet “RAP_Binders,” HMA Tools performs all needed grading calculations, and the final grading information appears at the bottom of the worksheet. 166 A Manual for Design of Hot Mix Asphalt with Commentary Critical Temperature Criteria Sample G*/sinδ =1.00 kPa As Recovered High Pavement Temperature G*/sinδ = 2.20 kPa RTFOT Aged Intermediate Pavement Temperature G*sinδ = 5000 kPa RTFOT Aged S = 300 MPa RTFOT Aged Low Pavement Temperature m = 0.300 RTFOT Aged Table 9-8. Criteria for determining critical temperatures.

Blending Charts For RAP Binders Linear blending charts are used to estimate the properties of blends of new binder and RAP binder. Figure 9-9 is a schematic of a linear blending chart. Separate blending charts for high, inter- mediate, and low temperature properties are used. Equation 9-3 describes the line in Figure 9-9. where Tc(Blend) = critical temperature for the blend of RAP and new binder Tc(New) = critical temperature for the new binder Tc(RAP) = critical temperature for the RAP binder %RAPB = percentage of total binder content obtained from the RAP, wt % T Blend T New RAPB T RAP T Newc c c C( ) = ( )+ ( )− ( )( )% 100 ( )9 3- Reclaimed Asphalt Pavement 167 Example Problem 9-4. Critical Temperatures for RAP Binder A sample of RAP binder was extracted, recovered, and tested to provide data for a blending chart analysis. Table 9-9 presents results of tests on the RAP binder as-recovered and after RTFOT conditioning. Determine the critical high, inter- mediate, and low temperatures for the RAP binder. Solution The binder test data from Table 9-9 are entered in the worksheet “RAP_Binders” in the appropriate cells in columns D and E. The continuous critical high temperature is given as 91.7°C in cell E75. The continuous critical intermediate temperature is 27.4°C and is given in cell E76. The continuous critical low temperature is −9.8°C, and is given in cell E77. The final binder grade for the recovered binder is PG 88-16, given in cell E73. Note that HMA Tools reports the binder grade by including the intermediate temperature grade in parentheses: PG 88-(28)-16. This is done because some agencies have requirements for intermediate temperature grade, and report- ing the grade in this way makes it easy to determine if such requirements are met. Critical Temperature Condition Property Method Temperature Test Result 88 °C 1.57 kPa As- Recovered G*/sinδ AASHTO T 315 94 °C 0.76 kPa 88 °C 4.06 kPa High RTFOT G*/sinδ AASHTO T 315 94 °C 2.14 kPa 25 °C 6,414 kPa Intermediate RTFOT G*/sinδ AASHTO T 315 28 °C 4,701 kPa -18 °C 440 MPa -12 °C 229 MPa RTFOT S AASHTO T 313 -6 °C 120 MPa -18 °C 0.220 -12 °C 0.281 Low RTFOT m AASHTO T 313 -6 °C 0.336 Table 9-9. Test results for extracted RAP binder for example 3.

The blending charts are based on the percentage of the total binder in the mixture that is from the RAP. As discussed earlier, the RAP added to a mixture includes both RAP aggregate and RAP binder. Because computer spreadsheets are now almost universally used to perform the calculations needed to perform HMA mix designs, including the potentially tedious calculations required when the design includes more than 15% RAP, it is not necessary to construct blending charts as part of the mix design process. If a blending chart is needed for an HMA mix design containing RAP, a detailed procedure can be found in AASHTO M 323. There are two different approaches to designing HMA mixtures with RAP so that the result- ing blended binder meets the required grade. The first is to establish the RAP content, and then determine the performance grade of the new binder needed to make sure the blended binder in the final mix is the proper grade. The second approach is to select the new binder grade, and then determine the required RAP content to ensure that the blended binder is the proper grade. A sur- prising twist on this second approach is that the required RAP content can be a maximum or a minimum. A maximum RAP content can occur when a relatively stiff new binder is used, so that addition of too much RAP will make the blended binder too stiff to meet the performance grade requirements at intermediate and/or low temperatures. A minimum RAP content can occur when a relatively soft new binder is used, in which case enough RAP must be added to provide sufficient stiffening to the blended binder so that high-temperature grade requirements are met. In some cases, there may be both minimum and maximum RAP content requirements. HMA Tools provides solutions for both types of RAP content calculation. Once appropriate binder grade information is entered along with the mix composition (aggregate blend data and volumetric data), HMA Tools will calculate the resulting blended binder grade and also estimate the minimum and maximum RAP contents based on binder grade requirements. If RAP from more than one stockpile is used in the mix design, HMA Tools assumes that the relative propor- tions of material in the RAP blend will remain constant as the overall RAP content varies. Two example problems below show how HMA Tools can be used in performing both types of binder grade calculations when designing HMA mixtures containing RAP. 168 A Manual for Design of Hot Mix Asphalt with Commentary -25 -20 -15 -10 -5 0 0 10 20 30 40 50 60 70 80 90 100 % RAP Binder Cr iti ca l T em pe ra tu re , C Tc(New) Tc(RAP) Figure 9-9. Linear blending chart.

Reclaimed Asphalt Pavement 169 Example Problem 9-5. Selection of a New Binder Grade for an HMA Mix Design Containing RAP The RAP binder from Example 4 will be used in an HMA mixture. The RAP will be added to the mixture at 30% of the aggregate blend by weight. The RAP has a binder content of 4.4%, and the HMA mixture has a binder content of 5.2%. Determine the new binder grade that should be used so that the blended binder meets the specification requirements for PG 64-22. Solution Information on the required binder grade is entered in the worksheet “Blended_Binders” in cells C5:C8—performance grade 64-22, high temperature grade 64°C, intermediate temperature grade 25°C and low temperature grade −22°C. The binder content of 5.20% is entered in cell C11, and an absorption value of 0.0 is entered in cell C12. Since only one RAP is being used, 100 is entered in cell C16, and cells C17:C19 are left blank. In cell C22 the RAP binder content of 4.40% is entered, with an absorption value of 0.0 entered in cell D22. Since only one RAP stockpile is being used, cells C23:D25 are left blank. The RAP binder being used is the same as already entered in the worksheet “RAP_Binders,” so the grading information (in the form of critical temperatures) appears in cells H30:J30. These values are then copied into cells C30:E30. Again, if more RAP stockpiles were used, additional grading information could be entered in cells C31:E33, but only one RAP is being used in this example so these cells are left blank. The RAP content of 30% by weight of total RAP plus aggregate is entered in cell C70. The required new binder grade of PG 58-28 is reported in the worksheet “Blended_ Binders” in cell C80. Note that the required critical temperatures for the new binder are given in cells C76:C78 as follows: high critical temperature—57.7°C, intermediate critical temperature—22.9°C, and low critical temperature—15.3°C. As in many other locations, HMA Tools reports the required grade by including the intermediate temperature grading of 19°C in parentheses, so cell C80 actually reads “58-(19)-28.” The worksheet “Blended_Binders” is designed to only provide one binder in this cell, although several others would typically meet the require- ments. The grade reported in cell C80 represents that with the lowest high temper- ature grade and the highest low temperature grade. For instance, in this example a PG 64-28 binder would also meet the grade requirements. When determining whether or not performance grades other than that listed in cell C80 would meet the requirements for an HMA design containing RAP, the engineer or technician must make certain that not only the high and low critical temperature require- ments are met, but also that the intermediate critical temperature requirement (cell C77) is met. In this example, a PG 64-28 binder would have a maximum intermediate critical temperature of 22°C and would therefore meet the speci- fied grading requirements. However, a PG 70-28 binder has a maximum interme- diate critical temperature of 25°C, which is greater than the calculated maximum intermediate critical temperature of 22.9°C and therefore should not be used in this mix design.

Handling RAP Materials in the Laboratory RAP materials must be handled differently than new aggregates when preparing specimens for volumetric design and performance analysis. First, the weight of the binder contained in the RAP must be accounted for during laboratory batching. Second, the RAP must be heated gently during the preparation of laboratory specimens to avoid changing the properties of the RAP binder. Recommended methods for handing RAP are discussed below. Laboratory Batching A supply of RAP for the preparation of laboratory specimens is obtained by combining the main portion of the individual samples for each stockpile and thoroughly mixing the combined material. Material for each RAP stockpile should be kept separate. Prior to batching, the RAP should be dried in an oven at 60 °C (140 °F) to remove field moisture. Laboratory batching is based on the weight of the aggregate, while the stockpile percentages used to produce the HMA at the hot-mix plant are based on total weight. When the HMA is composed of all new aggregates, the stockpile percentages can be used directly. However, when RAP stockpiles are used, the weight of the binder contained in the RAP must be accounted for and stockpile percentages based 170 A Manual for Design of Hot Mix Asphalt with Commentary Example Problem 9-6. Calculating the Maximum Allowable RAP Content Given an HMA Design with a Specific New Asphalt Binder The RAP binder from Example 4 will be used in an HMA mixture. A PG 64-22 binder with excellent low temperature characteristics is available, and the pro- ducer would like to use this binder in mixtures with RAP because of limited binder storage at the plant. The RAP has a binder content of 4.4%, and the HMA mixture has a binder content of 5.2%. Determine the amount of RAP that can be used with this binder to meet the specification requirements for PG 70-22. The critical temperatures for the new binder, based on historical data provided by the supplier, are Tc(High) = 66.0 °C, Tc(Int) = 19.3 °C, and Tc(Low) = −17.3 °C. Solution Much of the required information for this problem is the same as Example 5 and is entered in HMA Tools in the same way. The required continuous grade temper- atures for a PG 70-22 are Tc(High) = 70.0 °C, Tc(Int) = 28.0 °C, and Tc(Low) = −22.0 °C; these values are different from those for the PG 64-22 required in the previous example and should be entered in cells C6:C8. The critical temperatures for the new binder (PG 64-22) are entered in cells C44:C45 and C47. The minimum and maximum RAP contents, as a weight percentage of the total RAP plus aggregate weight, are given in cells C64 and C65, respectively: 33.5% minimum and 38.1% maximum. For the actual mix design, a value of 35% RAP would be a good choice. Note that for RAP contents of 15% and lower, the effects of RAP on binder grading need not be considered. Therefore, if HMA Tools calcu- lates that less than 15% RAP should be used in a mix because of binder grading considerations, a value of 15% is reported in cell C64. In a similar way, RAP con- tents above 50% are discouraged because of practical difficulties in handling such a quantity of RAP in many plants, so that the highest value HMA Tools will report in cell C65 is 50%, regardless of the value calculated on the basis of binder grading.

on the total weight of aggregate must be computed and used for laboratory batching. The required analysis was discussed earlier in the Blending and Variability section of this chapter. Example 1 illustrated the required computations. When preparing laboratory specimens, new aggregate stockpiles should be separated into the following size fractions: • Passing 37.5 mm—Retained 25.0 mm • Passing 25.0 mm—Retained 19.0 mm • Passing 19.0 mm—Retained 12.5 mm • Passing 12.5 mm—Retained 9.5 mm • Passing 9.5 mm—Retained 4.75 mm • Passing 4.75 mm—Retained 2.36 mm • Passing 2.36 mm Because of the relatively large amount of fine material in most RAP, it is not necessary to separate the RAP into size fractions for laboratory batching. The amount of each size fraction of new aggregate needed for a laboratory batch is computed directly from the proportions based on the total weight of aggregate. The amount of each RAP stockpile needed for a laboratory batch must be increased to account for the weight of binder in the RAP using Equation 9-4: where MRAP = mass of RAP required for the laboratory batch, g MRAPAGG = mass of RAP aggregate required for the laboratory batch, g PbRAP = RAP binder content, wt % The mass of binder provided by the RAP is then where MRAPBINDER = mass of RAP binder in the laboratory batch, g MRAP = mass of RAP in the laboratory batch, g PbRAP = RAP binder content, wt % HMA Tools can be used to perform these and all other required calculations for determining batch weights of mix designs containing RAP. Before determining batch weights for a mix design, all of the pertinent mix design data should be entered on various worksheets, including “General,” “Binders,” “RAP_Binders,” “Aggregates,” “RAP_Aggregates,” and “Trial_Batches.” Other data should be entered in the worksheet “Batch.” For cylindrical specimens, the diameter and height of up to three different-sized specimens are entered in cells F3:F5 and G3:G5, respectively. The numbers of specimens needed for each of these three different cylinder sizes are entered in cells I3:I5. The dimensions and number of specimens for up to two differently shaped beam-shaped specimens are entered in a similar way in cells F8:I9. If desired, an extra amount of loose mix can be entered in cell K3 (in grams)—this might be material needed for theoretical maximum specific gravity determinations. In addition to this loose mix, an extra percentage of material can be specified in cell O7. This represents a contingency, to ensure that enough material is available for the required specimens; 5 or 10% should normally be entered here. The user must also make sure to specify the trial batch number for the batch calculations in cell O1; this would be a number from 1 to 7, corresponding to the trial batch numbers in the worksheet “Trial_Batch.” M Pb MRAPBINDER RAP RAP= ⎛⎝⎜ ⎞⎠⎟ ×100 9 5( )- M M Pb RAP RAPAGG RAP = −( ) ×100 100 9 4( )- Reclaimed Asphalt Pavement 171

HMA Tools will calculate batch weights for each aggregate and RAP material, providing a complete breakdown for coarse material (retained on the 2.36-mm sieve) and three different breakdowns for fine aggregate: complete, partial (in two-sieve fractions), and with no break- down. HMA Tools also calculates the amount of new binder required—the amount of binder contributed by the RAP is automatically accounted for. The worksheet “Batch” is conveniently designed to print out a one page report that can be used to weigh out materials in the laboratory. The last example in this chapter shows how HMA Tools is used to calculate batch weights for mix designs containing RAP. 172 A Manual for Design of Hot Mix Asphalt with Commentary Example Problem 9-7. Laboratory Batching for an HMA Mix Design Containing RAP Laboratory specimens of the mixture from Example 1 will be prepared. The aggre- gate gradations were given previously in Table 9-1. The mixture will be produced using three new aggregate stockpiles, hydrated lime, and two RAP stockpiles. The stockpiles will be combined in the following proportions: 29% of Aggregate 1, 40% of Aggregate 2, 10% of Aggregate 3, 1% lime, 10% Coarse RAP, and 10% Fine RAP. The target VMA for the mix is 16.0% and the target air void content is 4.0%. Deter- mine batch weights for making two 150-mm-diameter by 100-mm-tall cylindrical specimens with 2,000 grams of extra material for performing a theoretical maxi- mum specific gravity test. Allow 5% extra material for contingency. The fine aggre- gate fraction (passing the 2.36-mm sieve) will not be further broken down, and the RAP will not be broken down at all. Calculate weights for this trial batch. Solution The aggregate and RAP data are entered into the worksheets “Aggregates” and “RAP_Aggregates” as for Example Problem 1. In the worksheet “Batch,” 1 should be entered for batch number in cell O1. Dimensions for the cylindrical specimen are entered in cells F3:G3, and 2 is entered for the number of specimens in cell I3. The amount of loose mix (2,000 g) is entered in cell K3, and 5% is entered in cell O7 for the desired amount of extra mix. After pressing shift+F9 to calculate, the batch weights appear on the lower portion of the spreadsheet. Table 9-10 sum- marizes the batch weights calculated by HMA Tools for this example. Material Total wt., g Fraction Mm Batch wt, g 12.5 – 9.5 267 9.5 – 4.75 2,136 4.75 – 2.36 386 Aggregate 1 - 2.36 179 9.5 – 4.75 82 4.75 – 2.36 1,514 Aggregate 2 4,091 -2.36 2,495 9.5 – 4.75 102 4.75 – 2.36 389 Aggregate 3 1,023 -2.36 532 Lime 102 All 102 CRAP 1,022 All 1,022 FRAP 1,023 All 1,023 New Binder 506 All 506 Total 10,735 Table 9-10. Summary of batch weights for example 7.

Heating RAP Exercise care when preparing laboratory specimens with RAP to avoid changing the properties of the RAP binder. The RAP should be heated for the shortest time possible to reach the mixing temperature. Heat the RAP for no more than 2 hours in a separate oven set to 110°C (230°F). Higher temperatures and longer heating times have been shown to change the properties of some RAP. The new aggregates should be heated from 10 to 20 °C above the mixing temperature before combining with the RAP and new binder. The mixture should be mixed, short-term aged, and compacted in the usual manner. Bibliography AASHTO Standards M 320, Standard Specification for Performance-Graded Asphalt Binder R 29, Grading or Verifying the Performance Grade of an Asphalt Binder T 2, Standard Method of Test for Sampling Aggregates T 248, Standard Method of Test for Reducing Samples of Aggregate to Testing Size T 308, Standard Method of Test for Determining the Asphalt Binder Content of Hot-Mix Asphalt (HMA) by the Ignition Method T 30, Standard Method of Test for Mechanical Analysis of Extracted Aggregates T 164, Standard Method of Test for Quantitative Extraction of Bitumen for Bituminous Paving Mixtures T 209, Standard Method of Test for Theoretical Maximum Specific Gravity and Density of Bituminous Paving Mixtures T 84, Standard Method of Test for Specific Gravity and Absorption of Fine Aggregate T 85, Standard Method of Test for Specific Gravity and Absorption of Coarse Aggregate T 176, Standard Method of Test for Plastic Fines in Graded Aggregates and Soils by Use of the Sand Equivalent Test T 319, Standard Method of Test for Quantitative Extraction and Recovery of Asphalt Binder from Asphalt Mixtures T 240, Standard Method of Test for Effect of Air on a Moving Film of Asphalt (Rolling Thin-Film Oven Test) T 315, Standard Method of Test for Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer (DSR) T 313, Standard Method of Test for Determining the Flexural Creep Stiffness of Asphalt Binder Using the Bending Beam Rheometer (BBR) Other Standards ASTM D 5821, Standard Test Method for Determining the Percentage of Fractured Particles in Coarse Aggregate ASTM D 4791, Standard Test Method for Flat Particles, Elongated Particles, or Flat and Elongated Particles in Coarse Aggregate Other Publications McDaniel, R., and R. M. Anderson (2001) NCHRP Report 452: Recommended Use of Reclaimed Asphalt Pavement in the Superpave Mix Design Method: Technician’s Manual, TRB, National Research Council, Washington, DC, 58 pp. McDaniel, R. S., et al. (2000) NCHRP Web-Only Document 30: Recommended Use of Reclaimed Asphalt Pavement in the Superpave Mix Design Method: Contractor’s Final Report, TRB, National Research Council, Washington, D.C., October, 461 pp. NAPA (2007) NAPA Quality Improvement Series 124: Designing HMA Mixtures with High RAP Content, NAPA, Lanham, MD NAPA (1996) Recycling Hot Mix Asphalt Pavement, Information Series 123, NAPA, Lanham, MD NAPA (2000) Recycling Practices for HMA, Special Report 187, NAPA, Lanham, MD, 2000. FHWA (1998) “User Guidelines for Waste and Byproduct Materials in Pavement Construction” FHWA-RD-97-148, FHWA, Washington, DC. Reclaimed Asphalt Pavement 173

Next: Chapter 10 - Design of Gap-Graded HMA Mixtures »
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TRB’s National Cooperative Highway Research Program (NCHRP) Report 673: A Manual for Design of Hot-Mix Asphalt with Commentary incorporates the many advances in materials characterization and hot-mix asphalt (HMA) mix design technology developed since the conclusion of the Strategic Highway Research Program (SHRP).

The final report on the project that developed NCHRP Report 673 and Appendixes C through F to NCHRP Report 673 were published as NCHRP Web-Only Document 159. The titles of the appendixes are as follows:

• Appendix C: Course Manual

• Appendix D: Draft Specification for Volumetric Mix Design of Dense-Graded HMA

• Appendix E: Draft Practice for Volumetric Mix Design of Dense-Graded HMA

• Appendix F: Tutorial

The companion Excel spreadsheet HMA tool and the training course materials described in NCHRP Report 673 are available for download from the Internet.

In January 2012, TRB released NCHRP Report 714: Special Mixture Design Considerations and Methods for Warm Mix Asphalt: A Supplement to NCHRP Report 673: A Manual for Design of Hot Mix Asphalt with Commentary. The report presents special mixture design considerations and methods used with warm mix asphalt.

In January 2012, TRB released an errata to NCHRP Report 673: Page 41, Table 4-7, and page 123, Table 8-10, respectively, should be replaced with a new table.

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