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CHAPTER 9 Reclaimed Asphalt Pavement Chapter 9 of the Manual deals with incorporation of reclaimed asphalt pavement (RAP) into HMA mix designs. This is a complicated topic potentially involving numerous calculations: 1. Calculation of the blended aggregate gradation, including contribution from the RAP. 2. Calculation of the binder content, again including contribution from the RAP. 3. Calculation of the blended binder grade, based upon both the new binder added and the binder contributed from the RAP. 4. Calculation of the required new binder grade needed to achieve a specified binder grade, given a certain RAP content and a binder grade for the RAP binder. 5. Calculation of the minimum and maximum RAP that can be used in a mix, given a new binder grade and a grade for the RAP binder. 6. Estimation of the variability in aggregate gradation and binder content, given a job mix formula (JMF) containing a certain amount of RAP. 7. Estimation of the maximum amount of RAP that can be used in a mix without exceeding typ- ical limits on variability of production, given variability in the RAP stockpiles being used. The mathematics of some of these calculations--in particular the variability calculations-- can be challenging. For this reason, HMA Tools has been designed to perform these calculations, and the Manual in general simply discusses how to use this spreadsheet to perform the needed calculations during the mix design process. This avoids having to show and document some involved equations. The Commentary for Chapter 9 therefore involves showing and describing the equations used in HMA Tools to perform these RAP calculations, along with any associated assumptions and/or simplifications. Chapter 9 is structured for the most part as a series of example problems of increasing com- plexity. The section below, on critical tables, figures, and equations therefore is mostly organized on the basis of these examples, presenting and describing the critical information used in solving each example problem. Calculations involving RAP binder properties are based on Appendix A of AASHTO M 323 and are not documented in detail here. Much of what is contained in Chapter 9 of the Manual has been based on NCHRP Report 452 (46). This is an excellent reference for technicians and laboratory engineers responsible for the design and/or analysis of HMA mix designs containing RAP. Example 1. Gradation and Binder Content Analysis for an HMA Mixture Containing RAP 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 253

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254 A Manual for Design of Hot Mix Asphalt with Commentary 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. The binder included in the RAP is computed from Equation 8: PbRAPi wbRAPi = psRAPi (8) 100 where wbRAPi = weight of RAP binder from RAP stockpile i, wt% psRAPi = percentage of RAP stockpile i in the total blend,% PbRAPi = binder content of RAP stockpile i, wt% The total weight of binder contributed by all RAP stockpiles is the sum of the weight con- tributed by each RAP stockpile and is computed from Equation 9: j wbRAPTotal = wbRAPi (9) i =1 where wbRAPTotal = total weight of RAP binder from all RAP stockpiles, weight% wbRAPi = weight of RAP binder from RAP stockpile i, wt% j = total number of RAP stockpiles The total binder content for the mix is simply calculated by adding the weight of binder con- tributed by all RAP stockpiles to the weight of new binder added. For gradation analysis, the percentage of each stockpile based on the total weight of aggregate is needed. The percentage of each new aggregate stockpile based on the total weight of aggregate is given by Equation 10: psnewk pnewk = 100% (10) (100 - wbRAPTotal ) where Pnewk = percentage of new aggregate k, weight% of total aggregate psnewk = percentage of new aggregate stockpile k in the total blend, weight% wbRAPTotal = total weight of RAP binder from all RAP stockpiles, weight% The percentage of each RAP aggregate based on the total weight of aggregate is given by Equation 11: psRAPi - wbRAPi pRAPi = 10 00% (11) (100 - wbRAPTotal ) where pRAPi = percentage of RAP aggregate i, weight% of total aggregate psRAPi = percentage of RAP stockpile i in the total blend, weight% wbRAPi = weight of RAP binder from RAP stockpile i, weight% wbRAPTotal = total weight of RAP binder from all RAP stockpiles, weight% For each sieve, the gradation of the blend of the stockpiles is then computed using the per- centage of each stockpile based on the total weight of aggregate using Equation 12: n pnewk j pRAPi tpp = ppk + ppi (12) k =1 100 i =1 100

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Commentary to the Mix Design Manual for Hot Mix Asphalt 255 where tpp = total percent passing a given sieve, weight% of total aggregate Pnewk = percentage of new aggregate k, weight% of total aggregate pRAPi = percentage of RAP aggregate i, weight% of total aggregate ppk = percent passing a given sieve for new aggregate k, weight% ppi = percent passing a given sieve for RAP aggregate i, weight% j = number of RAP stockpiles n = number of new stockpiles Example 2. Calculation of Mean, Standard Deviation, and Maximum Allowable RAP Content for a Single RAP Stockpile The mean is calculated using Equation 13 (47): n Xi X = (13) i =1 n where _ X = stockpile average Xi = result for location i n = total number of locations tested The standard deviation is calculated using Equation 14 (47): n ( Xi - X ) 2 i =1 s= (14) n -1 where _s = standard deviation X = stockpile average Xi = result for location i n = total number of locations tested Derivation of the procedure for calculation of the maximum allowable RAP content is as fol- lows. ASTM D 4460 gives equations for calculating standard deviation values for quantities deter- mined from calculations involving two other values. From these equations, the following formula for calculating the standard deviation of a blend of two materials can be derived: m = 2a ( ) b ( a b) a 2 2 + 1- 2 + X 2 + X 2 2 (15) where m = standard deviation of the mixture a = standard deviation of component "a" b = standard deviation of component "b" = proportion of component "a" in the mixture _ _a = mean value for component "a" X Xb = mean value for component "b" = standard deviation of the proportions

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256 A Manual for Design of Hot Mix Asphalt with Commentary We can rewrite this for percent passing for a selected sieve for HMA mixtures consisting of a blend of new HMA materials with RAP: PM = w R PR + w N PN + ( PR + PN ) w 2 2 2 2 2 2 2 (16) where PM = standard deviation of percent passing for a selected sieve for the mixture with RAP wR = weight fraction of RAP in the mixture PR = standard deviation of percent passing for the selected sieve for the RAP wN = weight fraction of new materials (new HMA) in the mixture = (1 - wR) _PN = standard deviation of percent passing for the selected sieve for the new HMA _ R = mean value for RAP% passing for the selected sieve P PN = mean value for new HMA% passing for the selected sieve w = standard deviation of the weight fractions, also called "batching variability," Equation 17 can be solved for the maximum amount of RAP that can be added to new material without increasing the standard deviation for percent passing on the selected sieve above a selected maximum value by application of the quadratic equation -b + b 2 - 4ac Max . RAP % = 100% (17) 2a where Max. RAP% = maximum amount of RAP that can be added to the mix, weight% a = 2 PR + PN 2 b = - 2 2 PN_ _ c = 2 PN + (P PN + P N) w - PM/Max 2 2 2 2 and PM/Max is the maximum allowable standard deviation for percent passing for the selected sieve. Equations 1 and 2 can be rewritten for asphalt content rather than for aggregate percent pass- ing, calculated using the following equation: BM = w R BR + w N BN + ( BR + BN ) w 2 2 2 2 2 2 2 (18) where BM = standard deviation of binder content (weight%) for the mixture with RAP wR = weight fraction of RAP in the mixture BR = standard deviation of binder content (weight%) for the RAP wN = weight fraction of new materials (new HMA) in the mixture = (1 - wR) _ BN = standard deviation of binder content (weight%) for the new HMA _ R = mean value for the RAP binder content, weight% B BN = mean value for new HMA binder content, weight% w = standard deviation of the weight fractions or "batching variability" As for Equation 1, Equation 3 can also be solved for the maximum amount of RAP that can be added to new material without increasing the variability above a selected maximum by appli- cation of the quadratic equation: -b + b 2 - 4ac Max . RAP % = 100% (19) 2a

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Commentary to the Mix Design Manual for Hot Mix Asphalt 257 where Max. RAP% = maximum amount of RAP that can be added to a mix without increasing the production variability, weight% a = 2 BR + BN 2 b = -2BN _ _ 2 c = 2 BN + (B R + B N)w - BM/Max 2 2 2 2 and BM/Max is the maximum allowable standard deviation for binder content for the entire mix, including RAP. The approach used in the Manual in applying Equations 17 and 19 to calculate the maximum allowable RAP in an HMA mix design is to assume that the maximum allowable standard devia- tion for the final HMA should be no larger than the standard deviation for the new materials in the mix. This is equivalent to saying that the amount of RAP should be limited so that the overall variability in HMA production is not increased above what it would normally be without the addition of any RAP. This approach simplifies some of the calculations, and as discussed below, if typical variability in aggregate% passing and binder contents are assumed, the mix designer can determine the maximum allowable RAP without knowing the existing HMA variability or the maximum allowable variability desired by the producer. The maximum amount of RAP that can be added to a mix simply becomes a function of the RAP variability. A critical issue in this approach is what values to use for typical standard deviations for HMA production when applying Equations 17 and 19. The simplest and most conservative approach is to base the standard deviation values on information given in ASTM D 3515: Standard Speci- fication for Hot-Mixed, Hot-Laid Bituminous Paving Mixtures. Although this document does not specify standard deviations for aggregates and asphalt binder, it does give tolerances; these are shown in Table 22. The question becomes what is the ratio between these tolerances and typical standard deviations? The standard deviation values corresponding to those given in ASTM D 3515 must be much smaller than the tolerances, otherwise, plants would often violate these specified tolerances. For example, if typical standard deviation values were one-fourth the specified toler- ance, HMA plants would exceed these limits one time in 20. This is probably too frequent; a somewhat smaller standard deviation is more likely--one-fifth of the specified tolerance range appears to provide reasonable estimates of typical standard deviation values in well-run HMA plants (typical variability of HMA production is discussed in more detail in Chapter 12 of the Manual and the Commentary). The resulting estimated typical standard deviations are also shown in Table 22. A second complication arises from the uncertainty in estimating standard deviations. When sev- eral samples of RAP are taken and used to estimate the standard deviation, the resulting value is an estimate. In fact, unless the number of replicate samples is about 30 or higher, the uncertainty Table 22. Production Tolerances for Hot Mix Plants as Given in ASTM D 3515. Typical Standard Sieve Size Tolerance Deviation > 12. 5 mm 8.0% 3.2% 4.75 and 9.5 mm 7.0% 2.8% 1.18 and 2.36 mm 6.0% 2.4% 0.300 and 0.600 mm 5.0% 2.0% 0.150 mm 4.0% 1.6% 0.075 mm 3.0% 1.2% Asphalt binder 0.5% 0.2%

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258 A Manual for Design of Hot Mix Asphalt with Commentary in the estimate can be quite large. To be conservative and to make certain that the variability in plant production will not be increased to an unacceptable level by the addition of RAP, an upper confidence limit for the standard deviation should be used, rather than the actual calculated value. This upper confidence limit is calculated using the following equation (47): (n - 1) s 2 U= (20) 2 ( ; n - 1) where U = upper confidence limit for the standard deviation at 1- confidence level; use in place of PR and/or BR in Equations 2 and 4. n = number of measurements used in estimating the standard deviation s 2 = chi-squared distribution with confidence level 1- and n-1 degrees of freedom A value for of 0.20 (an 80% confidence level) appears to provide reasonable values for U and the resulting calculated maximum allowable RAP contents. One advantage to using an upper confidence limit U for the standard deviation, rather than the actual estimate, is the effect of sam- ple size on the resulting value of U--the larger the number of RAP samples used to estimate the standard deviation, the lower will be the value of U and the greater the resulting maximum allow- able RAP content. Producers who take large numbers of RAP samples to characterize their stock- pile will be rewarded, while those using only a few samples will be severely limited in how much RAP they can use in their mixtures. For example, for the case where PN = PM/max = 2.0, and PR is estimated to be 4.0, if the RAP standard deviation is based on n = 5 samples, the maximum allowable RAP content is 17%. However, if the RAP standard deviation is based on n = 10 sam- ples, the maximum allowable RAP content increases to 27%. A third important question in applying the equations for analyzing the effect of RAP on HMA production variability is what is a typical value for the standard deviation of the proportions, also called "batching variability." Information is given in ASTM D 995: Standard Specification for Mixing Plants for Hot-Mixed, Hot-Laid Bituminous Paving Mixtures on the required accuracy of aggregate scales, control of automated plants, and related information that can be used to estab- lish typical blending standard deviations for HMA plants: The accuracy of metering of asphalt binder must be within 1.0% when compared to another metering device or to within 0.5% when compared to test weights. Assuming a 2 s precision applies to the comparison with test weights, this implies a blending standard deviation for asphalt binders of 0.25% or 0.0025. Aggregate scales for batch plants must also be accurate to within 0.5% when compared to test weights, again, implying a blending standard deviation of 0.25% or 0.0025. Automatic proportioning systems, for both batch plants and drum plants, must batch aggre- gate (other than mineral filler) to within 1.5% of the total batch weight, or for continuous drum plants, to within 1.5% of the mix production per drum rotation/unit time. Assuming that this tolerance refers to comparison with test weights or similarly accurate reference, and that a 2 s precision is implied, this translates to a blending standard deviation of 0.75% or 0.0075. The required tolerance for mineral filler is 0.5%, implying a blending standard deviation of 0.0025. For asphalt binder, the required tolerance is 0.1%, implying a blending standard deviation of 0.0005. Assuming that the tolerance for adding RAP to a mix is similar to that for aggregate, and con- servatively applying the standard deviation calculated from the required tolerance for automated plants, the blending standard deviation for analyzing RAP variability should be 0.0075. It should be noted that this is based on the maximum permitted tolerance in automated plants and is thus

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Commentary to the Mix Design Manual for Hot Mix Asphalt 259 Standard Deviation for RAP Aggregate % Passing, % 0 1 2 3 4 5 6 7 8 50 Max. RAP Content, Wt. % 40 30 20 10 Sieve size, mm: 0.075 0.150 0.300 1.18 4.75 > 9.5 to 0.600 to 2.36 to 9.5 Figure 7. Maximum RAP content as a function of RAP aggregate sieve size and standard deviation (Figure 9-3 in the Mix Design Manual). a conservative assumption. The actual blending variability in many plants will probably be lower than this. HMA Tools calculates mean, standard deviation, the upper confidence limit for standard devi- ation, and the maximum allowable RAP content based on variability for up to four different RAP stockpiles. This analysis uses Equations 13 through 20 along with the assumptions described con- cerning typical variability in HMA production and batching variability. Example 3. Determination of Maximum Allowable RAP Content Based on Variability Analysis Using the Graphical Approach This example problem is essentially identical to the previous one, but in this case a simplified graphical approach is used in determining the maximum allowable RAP. This approach involves the use of four charts--Figures 9-3 through 9-6 in the Manual--to determine the maximum allow- able RAP content. These charts are reproduced here for the convenience of the reader. The charts have been developed based on the analysis described above, with a sample size of N = 5; the sam- ple size is small because it has been assumed that those producers wishing to use this simplified approach would probably not want to use large sample sizes of RAP. Figures 7 and 8 (9-3 and 50 Max. RAP Content, Wt. % 45 40 35 30 25 20 15 0.2 0.3 0.4 0.5 0.6 0.7 Binder Standard Deviation Figure 8. Maximum RAP content as a function of standard deviation for asphalt binder content (Figure 9-4 in the Mix Design Manual). For n = 5 Samples from a single RAP stockpile.

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260 A Manual for Design of Hot Mix Asphalt with Commentary 9-4 in the Manual) are for the case where only a single RAP stockpile is used in a mix design. The development of these charts was straightforward, involving a direct application of the equations given above. As an example of using these charts, if a given RAP stockpile has a standard devia- tion of 4.0% for aggregate passing the 0.60 mm sieve, the maximum allowable RAP content can be found from Figure 7 to be 30%. It must be emphasized that Figure 7 is based on standard devi- ations calculated using at least 5 samples--it should not be applied to standard deviations calcu- lated using a lower number of samples. It can be used for standard deviations calculated using larger samples, but the results will be overly conservative. Also, in developing these figures it is assumed that the difference in percent passing between the RAP aggregate and the new aggre- gate will not exceed these limits: 30% for mineral filler; 40% for passing the 0.150 mm sieve, and 50% for all other aggregate sizes. If the differences exceed these limits, the difference term in Equations 15 through 18 starts to become significant and must be considered in the calculation. In using Figure 7 in an actual mix design, all aggregate sizes would be evaluated, and the overall maximum allowable RAP content would be the lowest value calculated for all sieve sizes. The maximum RAP content based on asphalt binder standard deviation should also be evaluated (Figure 8, or Figure 9-4 in the Manual)--again, the lowest calculated of these maximum RAP contents should be applied. Figures 7 and 8 will in general not be accurate when more than one RAP stockpile is used in a mix design. This is because as RAP stockpiles are blended, the variability of the resulting stockpile will be reduced. The more stockpiles in a blend, the lower will be its variability when compared to the average variability for the materials in the blend. The standard deviation for % passing and binder content for a blend of three or more RAP stockpiles can be accurately estimated by sequen- tial application of Equations 15 and 17, respectively. This calculation is done as follows. The stan- dard deviation for % passing for a blend of Stockpiles 1 and 2 is first calculated. Then, the standard deviation is calculated for a second blend, made up of stockpile 3 and the blend of Stockpiles 1 and 2. If a fourth stockpile is used, the standard deviation for a blend of Stockpile 4 and the blend of Stockpiles 1, 2, and 3 is calculated. This is done for both aggregate % passing and binder content. This approach is very accurate and is used in HMA Tools in calculating the standard deviation values for RAP blends involving more than two stockpiles. Unfortunately, constructing graphs similar to Figures 7 and 8 for this situation is somewhat complicated. The approached used for the Manual was to develop an empirical relationship between the average standard deviation of a blend of stockpiles and the standard deviation calculated using Equations 15 and 17. The data was generated using a Monte Carlo approach. A total of 500 data points were generated, with simulated RAP stockpile blends composed of from two to four separate stockpiles, having a wide range of standard deviations along with a wide range of blend compositions. The relationships between average standard deviation and cal- culated standard deviation for % passing is shown in Figure 9, and for binder content in Fig- ure 10. These plots include the regression function for predicted standard deviation, along with the 80% upper prediction limit. In order to provide a conservative estimate of standard deviation, the upper prediction limits were used in generating the charts for determining maximum RAP content in HMA designs using more than one stockpile. The equation for estimating the 80% upper prediction limit for standard deviation of a blend of RAP stock- piles for aggregate% passing is as follows: -- SD ( PP , 80% UPL ) = 0.70 SD1.023 (21) where SD(PP, 80% UPL) = Estimated standard deviation for % passing for the overall RAP stockpile blend, 80% upper prediction limit -- SD = average standard deviation for % passing for the RAP stockpile blend

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Commentary to the Mix Design Manual for Hot Mix Asphalt 261 10.0 Overall RAP Std. Dev. 1.0 Data Predicted Std. Dev. 80 % Upper Prediction Limit 0.1 1.0 10.0 Average RAP Standard Deviation for % Passing Figure 9. Relationship between average RAP standard deviation for % passing and calculated overall RAP standard deviation for % passing. The 80% upper prediction limit for standard deviation of the binder content for a blend of RAP stockpiles can be estimated using the following equation: SD ( BC , 80% UPL ) = 0.69 SD 0.973 (22) where SD(BC, 80% UPL) = Estimated standard deviation for binder content (weight%) for the over- all RAP stockpile blend, 80% upper prediction limit -- SD = average standard deviation for binder content (weight %) for the RAP stockpile blend Using Equations 21 and 22, Figures 11 and 12 were developed, respectively, showing maxi- mum allowable RAP content as a function of average RAP standard deviation values. It should be noted that these charts are conservative and like Figures 7 and 8 are based on standard devi- ation values calculated using N = 5 independent samples of RAP. HMA Tools uses the pertinent equations directly, without any assumptions or simplifications. HMA Tools will therefore pro- vide more accurate estimates of maximum allowable RAP contents. Furthermore, in general, the estimated maximum RAP contents found using HMA Tools will be somewhat larger than those found with the charts. This is especially true when more than five samples of RAP are used in esti- mating standard deviation values, when more than one RAP is used in a mix design, or both. 1.0 Overall RAP Std. Dev. 0.1 Data Predicted Std. Dev. 80 % Upper Prediction Limit 0.0 0.1 1.0 Average RAP Standard Deviation for Binder Content Figure 10. Relationship between average RAP standard deviation for binder content and calculated overall RAP standard deviation for binder content.

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262 A Manual for Design of Hot Mix Asphalt with Commentary Average Standard Deviation for RAP Aggregate % Passing 0 1 2 3 4 5 6 7 8 9 10 50 Max. RAP Content, Wt. % 45 40 35 30 25 20 15 Sieve size, mm: 0.075 0.150 0.300 1.18 4.75 > 9.5 & 0.600 & 2.36 & 9.5 Figure 11. Maximum RAP content as a function of average standard deviation for aggregate % passing (Figure 9-5 in the Mix Design Manual). For n = 5 Samples from a blend of RAP stockpiles, and no stockpile making up more than 70% of the RAP blend. Calculation of Aggregate Specific Gravity Values for RAP Stockpiles. 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 deter- mine the bulk specific gravity of the RAP aggregate (46). 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 RAP aggregate after removing the binder with the ignition oven or solvent extraction. Details of these approaches are discussed below (46). 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 23 (Equation 9-1 in the Manual) (46): 50 Max. RAP Content, Wt. % 45 40 35 30 25 20 15 0.2 0.3 0.4 0.5 0.6 0.7 Average Binder Standard Deviation Figure 12. Maximum RAP content as a function of average standard deviation for asphalt binder content (Figure 9-6 in the Mix Design Manual). For n = 5 Samples from a blend of RAP stockpiles, and no stockpile making up more than 70% of the RAP blend.

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Commentary to the Mix Design Manual for Hot Mix Asphalt 263 (100 - Pb ) Gse = (23) 100 Pb - Gmm Gb 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 24 (Equa- tion 9-2 in the Manual), which is a rearranged version of the equation used in volumetric analy- sis to compute asphalt absorption. Gse Gsb = (24) ba se P G +1 100 Gb where Gsb = estimated bulk specific gravity of the RAP aggregate Gse = effective specific gravity of the RAP aggregate from Equation 23 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 the preci- sion of the maximum specific gravity measurement, 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 that was 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 bulk specific gravity of the RAP binder is small. For a typi- cal mixture it is only 0.002 for a 0.010 error in the bulk specific gravity of the binder. Poten- tial errors associated with errors in the RAP binder content or the RAP binder absorption are significantly larger. These errors are shown in Figure 13 for RAP having a maximum specific gravity of 2.500, a total binder content of 4.0%, 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 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 spe- cific gravity and binder content of the RAP depends mostly on the accuracy of the estimated cor- rection 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 similar accuracy as those mea- sured 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 sam- ples from at least three locations in the RAP stockpile.

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264 A Manual for Design of Hot Mix Asphalt with Commentary 0.040 RAP Binder Content RAP Binder Absorption ERROR IN BULK SPECIFIC GRAVITY OF RAP 0.030 0.020 0.010 AGGREGATE 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, % Figure 13. Potential errors in bulk specific gravity of the RAP aggregate for errors in RAP binder content and binder absorption (Figure 9-7 in the Mix Design Manual). Measuring RAP Aggregate Specific Gravity If a reasonable estimate of the binder absorption for the RAP is not available, the specific grav- ity 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 has been designed so that either approach can be used to estimate RAP aggregate specific gravity values. If the specific gravity values are to be estimated from maximum theoret- ical specific gravity, binder content, and related information, the data is entered in cells C6:F9 in 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 grav- ity for each of up to four RAP stockpiles then appear in cells C16:F17. If data for both 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 Binder Properties The section in the Manual on RAP binder properties is based on information and equations given in Appendix A of AASHTO M 323. The various equations and calculations described herein have been implemented in HMA Tools. Using HMA Tools to perform calculations related to RAP binder properties should give results identical to manual calculations carried out following the instructions given in Appendix A of AASHTO M 323.