Supporting Materials for NCHRP Report 673 (2011)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Recommended Standard Specification for Volumetric Mix Design of Dense-Graded HMA NCHRP 9-33 Designation M 1 1. SCOPE 1.1. This specification for volumetric mix design uses aggregate and mixture properties to produce a hot mix asphalt (HMA) job mix formula. 1.2. This standard specifies minimum quality requirements for binder, aggregate, and dense-graded HMA mix designs. 1.3. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of the user of this procedure to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards:  M 320, Performance-Graded Asphalt binder  R 29, Grading or Verifying the Performance Grade of an Asphalt Binder  T 11, Materials Finer Than 75-µm (No. 200) Sieve in Mineral Aggregates by Washing  T 27, Sieve Analysis of Fine and Coarse Aggregates  T 164, Quantitative Extraction of Bitumen from Bituminous Paving Mixtures  T 170, Recovery of Asphalt from Solution by Abson Method  T 176, Plastic Fines in Graded Aggregates and Soils by Use of the Sand Equivalent Test  T 240, Effect of Heat and Air on a Moving Film of Asphalt (Rolling Thin- Film Oven Test)  T 283, Resistance of compacted Asphalt Mixtures to Moisture-Induced Damage  T 304, Uncompacted Void Content of Fine Aggregate  T 308, Determining the Asphalt Binder Content of Hot-Mix Asphalt (HMA) by the Ignition Method  T 312, Preparing and Determining the Density of Hot-Mix Asphalt (HMA) Specimens by Means of the Superpave Gyratory compactor  T 319, Quantitative Extraction and Recovery of Asphalt Binder from Asphalt Mixtures 161

2.2. ASTM Standards:  D 4791, Flat Particles, Elongated Particles, or Flat and Elongated Particles in Coarse Aggregate  D 5821, Determining the Percentage of Fractured Particles in Coarse Aggregate 2.3. Asphalt Institute Publication:  MS-2, Mix Design Methods for Asphalt Concrete and Other Mix Types 2.4. National Asphalt Pavement Association Publication  IS 128, HMA Pavement Mix Type Selection Guide 2.5. Other References:  Recommended Standard Practice M 2, Design of Dense-Graded HMA  LTPP Seasonal Asphalt Concrete Pavement Temperature Models. FHWA- RD-97-103, FHWA, U.S. Department of Transportation, Washington, DC, September 1988.  LTPPBind can be downloaded at http://ltpp-products.com/OtherProducts.asp 3. TERMINOLOGY 3.1. HMA—hot mix asphalt 3.2. design ESALs—Design equivalent (80 kN) single axle loads, normally specified over a 20-year design life. 3.2.1. Discussion—design ESALs are the anticipated project traffic level expected on the design lane over the design life of the pavement. 3.3. air voids (Va)—The total volume of the small pockets of air between the coated aggregate particles throughout a compacted paving mixture, expressed as a percent of the bulk volume of the compacted paving mixture (Note 1) Note 1—Term defined in Asphalt Institute Manual MS-2, Mix Design Methods for Asphalt Concrete and Other Mix types. 3.4. voids in the mineral aggregate (VMA)—The volume of the intergranular void space between the aggregate particles of a compacted paving mixture that includes the air voids and the effective binder content, expressed as a percent of the total volume of the specimen (Note 1). 3.5. absorbed binder volume (Vba)—The volume of asphalt binder in a mixture absorbed into the permeable voids in the aggregate. 162

3.6. effective binder volume (Vbe)—The volume of asphalt binder in a mixture, excluding the volume of binder absorbed by the aggregate. 3.7. voids filled with asphalt (VFA)—the percentage of the VMA filled with binder (the effective binder volume divided by the VMA). 3.8. dust-to-binder ratio (P0.075/Pbe)—By mass, the ratio between the percent of aggregate passing the 75-µm (No. 200) sieve (P0.075) and the effective binder content (Pbe). 3.9. nominal maximum aggregate size—One size larger than the first sieve that retains more than 10 percent aggregate (Note 2). 3.10. maximum aggregate size—One size larger than the nominal maximum aggregate size (Note 2). Note 2—The definitions given in Sections 3.7 and 3.8 also apply to Superpave mixes, but differ from the definitions published in other AASHTO standards. 3.11. reclaimed asphalt pavement (RAP)—Pavement materials, removed, processed, or both, containing asphalt binder and aggregate. 3.12. primary control sieve (PCS)—The sieve defining the break point between fine- and coarse-graded mixtures for each nominal maximum aggregate size, as defined in Table 5 below. 4. SIGNIFICANCE AND USE 4.1. This standard may be used to select and evaluate materials for dense-graded HMA volumetric mix designs. 5. BINDER REQUIREMENTS 5.1. The binder shall be a performance-graded (PG) binder, meeting the requirements of AASHTO M 320, which is appropriate for the climate and traffic-loading conditions at the site of the paving project or as specified by the contract documents. 5.1.1. In most cases, binder grade selections should follow specifications established by the agency. 5.1.2. In cases where specifications for binder grade selection have not been established by the agency, or where unusual traffic loading or environmental conditions make such specifications suspect, the following procedure may be used to determine binder grade. 163

5.1.2.1. Determine the mean and the standard deviation of the yearly, 7-day-average, maximum pavement temperature, measured 20 mm below the pavement surface, and the mean and the standard deviation of the yearly, 1-day-minimum pavement temperature, measured at the pavement surface, at the site of the paving project. These temperatures can be determined by use of the LTPPBind software or be supplied by the specifying agency. Often, actual site data is not available, and representative data from the nearest weather station will have to be used. 5.1.2.2. Using the latest available version of LTPPBind software, the maximum and minimum pavement temperatures determined in 5.1.2.1, and a reliability level of 98%, determine the required binder grade for a traffic level less than 0.3 million ESALs and standard traffic speed. 5.1.2.3. For traffic levels of 0.3 million ESALs or more, for traffic speeds of 70 km/h or less, or both, adjust the binder grade determined in 5.1.2.2. according to the grade adjustments given in Table 1. Table 1—High Temperature Binder Grade Adjustments for Traffic Level and Speed Traffic Speed Category: Very Slow Slow Fast Traffic speed, mph (kph): < 15 (< 25) 15 to < 45 (25 to < 70) ≥ 45 (≥ 70) 20-year Design Traffic (MESALs) Grade Adjustment for Traffic Speed Level Given Above and Design Traffic Level at Left: < 0.3 --- --- --- 0.3 to < 3 2 1 --- 3 to < 10 3a 2 1 10 to < 30 4a 3a 2 ≥ 30 4a 4a 3a a Consider use of polymer-modified binder. If a polymer-modified binder is used, high temperature grade may be reduced one grade (6°C) provided rut resistance is verified using suitable performance testing. Note 4—The grade adjustments in Table 1 should not necessarily be applied to “base” binder grades specified by the agency, since such “base” binder grades are normally already adjusted for traffic level and speed. 5.2. If RAP is to be used in the mixture, and the RAP content is not greater than 15% by total mix weight, the binder grade can be selected as described in 5.1. If the RAP content is greater than 15% by total mix weight, the blended binder grade, as determined following the procedure given in the Appendix to this standard or some equivalent method, must meet the requirements as described in 5.1. 6. COMBINED AGGREGATE REQUIREMENTS 6.1. Size Requirements 164

6.1.1. Nominal Maximum Size—The combined aggregate shall have a nominal maximum aggregate size of 4.75 to 19.0 mm for HMA surface courses and no larger than 37.5 mm for HMA subsurface courses. Recommended nominal maximum aggregate sizes for different applications and lift thicknesses are given in Table 2. Table 2—Recommended Aggregate Nominal Maximum Aggregate Sizes for Dense-Graded HMA Mixtures Application Recommended NMAS, mm Minimum Lift Thickness, mm Fine-Graded Mixtures Coarse-Graded Mixtures Leveling course mixtures 4.75 15 to 25 20 to 25 9.5 30 to 50 40 to 50 Wearing course mixtures 4.75 15 to 25 20 to 25 9.5 30 to 50 40 to 50 12.5 40 to 65 50 to 65 Intermediate course mixtures 19.0 60 to 100 75 to 100 25.0 75 to 125 100 to 125 Base course mixtures 19.0 60 to 100 75 to 100 25.0 75 to 125 100 to 125 37.5 115 to 150 150 Rich base course mixtures 9.5 30 to 50 40 to 50 12.5 40 to 65 50 to 65 Note 5—Additional guidance on selection of the appropriate nominal maximum size mixture can be found in the National Asphalt Pavement Association’s publication IS 128. 6.1.2. Gradation Control Points—The combined aggregate should conform to the gradation recommendations listed in Table 3 (19.0-mm through 37.5-mm sizes) and Table 4 (4.75-mm through 12.5-mm sizes) when tested according to T 11 and T 27. 165

Table 3—Control Points for 19.0-mm through 37.5-mm Aggregate Gradations for Dense-graded HMA Mixtures Sieve Size (mm) Percent Passing for Nominal Maximum Aggregate Size: 37.5 mm 25.0 mm 19.0 mm Min. Max. Min. Max. Min. Max. 50.0 100 --- --- --- --- --- 37.5 90 100 100 --- --- --- 25.0 --- 90 90 100 100 --- 19.0 --- --- --- 90 90 100 12.5 --- --- --- --- --- 90 9.5 --- --- --- --- --- --- 4.75 --- --- --- --- --- --- 2.36 15 41 19 45 23 49 1.18 --- --- --- --- --- --- 0.600 --- --- --- --- --- --- 0.075 0 6 1 7 2 8 Table 4—Control Points for 4.75-mm through 12.5-mm Aggregate Gradations for Dense-graded HMA Mixtures Sieve Size (mm) Percent Passing for Nominal Maximum Aggregate Size: 12.5 mm 9.5 mm 4.75 mm Min. Max. Min. Max. Min. Max. 50.0 --- --- --- --- --- --- 37.5 --- --- --- --- --- --- 25.0 --- --- --- --- --- --- 19.0 100 --- --- --- --- --- 12.5 90 100 100 --- 100 --- 9.5 --- 90 90 100 95 100 4.75 --- --- --- 90 90 100 2.36 28 58 32 67 --- --- 1.18 --- --- --- --- 30 60 0.600 --- --- --- --- --- --- 0.075 2 10 2 10 6 12 6.1.3. Gradation Classification—The combined aggregate gradation shall be classified as coarse-graded when it passes below the primary control sieve (PCS) control point as defined in Table 5. All other gradations shall be classified as fine-graded. 166

Table 5—Gradation Classification and Primary Control Sieve Sizes Aggregate NMAS (mm) Primary Control Sieve (mm) PCS Control Point (% Passing) 4.75 1.18 42 9.5 2.36 47 12.5 2.36 39 19.0 4.75 47 25.0 4.75 40 37.5 9.5 47 6.2. Coarse Aggregate Fractured Faces Requirements—The aggregate shall meet the percentage of fractured faces requirements specified in Table 6 and measured according to ASTM D 5821. Table 6—Coarse Aggregate Fracture Faces Requirements. Design ESALs (million) Percentage of Particles with at Least One/Two Fractured Faces, for Depth of Pavement Layera, mm 0 to 100b Below 100b < 0.30 55 / --- --- / --- 0.3 to < 3 75 / --- 50 / --- 3 to < 10 85 / 80 60 / --- 10 to < 30 95 / 90 80 / 75 30 or more 98 / 98c 98/ 98c aDepth of pavement layer is measured from pavement surface to surface of pavement layer. bIf less than 25 percent of a construction lift is within 100 mm of the surface, the lift may be considered to be below 100 mm for mixture design purposes. cThe CAFF requirement for design traffic levels of 30 million ESALs or more may be reduced to 95/95 if experience with local conditions and materials indicate that this would provide HMA mixtures with adequate rut resistance under very heavy traffic. 6.3. Fine Aggregate Angularity Requirements—The aggregate shall meet the uncompacted void content of fine aggregate requirements specified in Table 7 and measured according to AASHTO T 304, Method A. 167

Table 7—Fine Aggregate Angularity Requirements Design ESALs (million) Depth of Pavement Layer from Surface, mm 0 to 100a Below 100a < 0.30 ---b --- 0.3 to < 3 40 --- 3 to < 10 45c 40 10 to < 30 45c 45c 30 or more 45c 45c Criteria are presented as percent air voids in loosely compacted fine aggregate. aIf less than 25 percent of a construction lift is within 100 mm of the surface, the lift may be considered to be below 100 mm for mixture design purposes. bAlthough there is no FAA requirement for design traffic levels below 0.30 million ESALS, consideration should be given to requiring a minimum uncompacted void content of 40 percent for 4.75 mm nominal maximum aggregate size mixes. cThe FAA requirement of 45 may be reduced to 43 if experience with local conditions and materials indicate that this would produce HMA mixtures with adequate rut resistance under the given design traffic level. 6.4. Sand Equivalent Requirements—Aggregates not derived from RAP shall meet the sand equivalent (clay content) requirements specified in Table 8 and measured according to AASHTO T 176. RAP aggregates need not meet the requirements of Table 8. Table 8—Maximum Clay Content Requirements Design ESALs (million) Minimum Sand Equivalency Value < 0.30 40 0.3 to < 3 40 3 to < 10 45 10 to < 30 45 30 or more 50 Criteria are presented as Sand Equivalent Value. 6.5. Flat-and-Elongated Requirements—The aggregate shall meet the flat-and- elongated requirements specified in Table 9 and measured according to ASTM D 4791, with the exception that material passing the 9.5-mm sieve and retained on the 4.75-mm sieve shall be included. The aggregate shall be measured using the ratio of 5:1, comparing the length (longest dimension) to the thickness (smallest dimension) of the aggregate particles. 168

Table 9—Criteria for Flat and Elongated Particles Design ESALs (million) Maximum Percentage of Flat and Elongated Particles at 5:1 < 0.30 --- 0.3 to < 3 10 3 to < 10 10 10 to < 30 10 30 or more 10 Criteria are presented as percent flat and elongated particles by mass. 6.6. When RAP is used in the mixture, the RAP aggregate shall be extracted from the RAP using a solvent extraction (AASHTO T 164) or ignition oven (AASHTO T 308) as specified by the agency. The RAP aggregate shall be included in determination of gradation, coarse aggregate fractured faces, fine aggregate angularity, and flat-and-elongated requirements. The sand equivalent requirements shall be waived for the RAP aggregate but shall apply to the remainder of the aggregate blend. 7. HMA DESIGN REQUIREMENTS 7.1. The binder and aggregate in the HMA shall conform to the requirements of Sections 5 and 6. 7.2. The HMA design, when compacted in accordance with AASHTO T 312 at the design number of gyrations, shall have an air void content of 4.0 ±0.5%. The VMA shall meet the requirements given in Table 10. The dust-to-binder ratio shall meet the requirements given in Table 11. 169

Table 10—VMA Requirements for Standard Dense-Graded Mixtures Aggregate NMAS (mm) Minimum VMAa (%) Maximum VMAa (%) 4.75 16.0 to 17.0 18.0 to 19.0 9.5 15.0 to 16.0 17.0 to 18.0 12.5 14.0 to 15.0 16.0 to 17.0 19.0 13.0 to 14.0 15.0 to 16.0 25.0 12.0 to 13.0 14.0 to 15.0 37.5 11.0 to 12.0 13.0 to 14.0 aThe specifying agency may establish minimum and maximum values for VMA within the stated ranges. Lower values for VMA will tend to produce HMA with improved rut resistance, while higher values for VMA will tend to produce HMA with better fatigue resistance and durability. Table 11—Requirements for Dust/Binder Ratio Mix Aggregate NMAS, mm Allowable Range for Dust/Binder Ratio, by Weight > 4.75 0.8 to 1.6a 4.75 0.9 to 2.0 aThe specifying agency may lower the allowable range for dust/binder ratio to 0.6 to 1.2 if warranted by local conditions and materials. However, the dust/binder ratio should not be lowered if VMA requirements are increased above the standard values as listed in Table 8-6. 7.3. The HMA design, when compacted according to T 312 at 7.0 ±0.5 percent air voids and tested in accordance with T 283 shall have a minimum tensile strength ratio of 0.80. APPENDIX A: PROCEDURES FOR BLENDED BINDER GRADE TESTING AND CALCULATIONS FOR HMA MIXTURES CONTAINING MORE THAN 15% RECLAIMED ASPHALT BY WEIGHT A1. Blending of RAP binders can be accomplished by knowing the desired final performance grade (critical temperature) of the blended binder, the physical properties (and critical temperatures) of the recovered RAP binder, and either the physical properties (and critical temperature) of the virgin asphalt binder or the desired percentage of RAP in the mixture. A2. Determine the physical properties and critical temperature of the RAP binder. A2.1. Recover the RAP binder using AASHTO T 319 (Note A1) with an appropriate solvent. At least 50 g of recovered RAP binder are needed for testing. Perform 170

binder classification testing using the tests in M 320. Rotational viscosity, flash point, and mass loss tests are not required. Note A1—While AASHTO T 319 is the preferred method, at the discretion of the agency, AASHTO T 170 may be used. Research conducted under NCHRP Project 9-12 (NCHRP Report 452 and NCHRP Research Results Digest 253) indicated that AASHTO T 170 might affect recovered binder properties. A2.2. Determine the percentage of binder that is contributed by the RAP using Equation A1: ( )( )       × − −× = 100 100 100 % RAPRAP RAPRAP Pbps Pb PbPbps RAPB (A1) where: %RAPB = percentage of total binder content that is obtained from the RAP, wt% RAPPb = binder content of RAP, wt% RAPps = stockpile percentage of RAP in the total blend, wt% Pb = binder content of the mixture, wt% A2.3. Determine G*/sinδ for the recovered binder in accordance with AASHTO T 315 at two temperatures: one resulting in G*/sinδ greater than 1.00 kPa, and one resulting in G*/sinδ less than 1.00 kPa. A2.3.1 Compute the As Recovered true high temperature grade to the nearest 0.1 degree using Equation A2.       − −× += )log()log( )()log( 21 121 1cov GG TTGTT eredreas (A2) where: Tas recovered = critical temperature where G*/sinδ equals 1.00 kPa for the as recovered RAP binder T1 = test temperature where G*/sinδ is closest to but above 1.00 kPa G1 = G*/sinδ for temperature T1, kPa T2 = test temperature where G*/sinδ is closest to but below 1.00 kPa G2 = G*/sinδ for temperature T2, kPa A2.4. Condition the remaining binder in accordance with AASHTO T 240. 171

A2.5. Determine G*/sinδ for the RRTFOT conditioned binder in accordance with AASHTO T 315 at two temperatures: one resulting in G*/sinδ greater than 2.20 kPa, and one resulting in G*/sinδ less than 2.20 kPa. A2.5.1. Compute the RRTFOT true high temperature grade to the nearest 0.1 degree using Equation A3. ( )       − −×− += )log()log( )(3424.0)log( 21 121 1 GG TTGTTRTFOT (A3) where: TRRTFOT = critical temperature where G*/sinδ equals 2.20 kPa for the RRTFOT conditioned RAP binder T1 = test temperature where G*/sinδ is closest to but greater than 2.20 kPa G1 = G*/sinδ for temperature T1, kPa T2 = test temperature where G*/sinδ is closest to but less than 2.20 kPa G2 = G*/sinδ for temperature T2, kPa A2.6. Determine G*×sinδ for the PAV conditioned binder in accordance with AASHTO T 315 at two temperatures; one resulting in G*×sinδ greater than 5,000 kPa and one resulting in G*×sinδ less than 5,000 kPa. A2.6.1. Compute the true intermediate temperature grade to the nearest 0.1 degree using Equation A4.       − −×− += )log()log( )()6990.3)(log( 21 121 1int GG TTGTT ermediate (A4) where: Tintermediate = critical temperature where G*×sinδ equals 5,000 kPa for the PAV conditioned RAP binder T1 = test temperature where G*×sinδ is closest to but above 5,000 kPa G1 = G*×sinδ for temperature T1, kPa T2 = test temperature where G*×sinδ is closest to but below 5,000 kPa G2 = G*×sinδ for temperature T2, kPa A2.7. Determine the low temperature creep stiffness, S, and m-value for the PAV conditioned binder in accordance with AASHTO T 313 at two temperatures; one resulting in S greater than 300 MPa, and one resulting in S less than 300 MPa. 172

A2.7.1. Compute the true low temperature grade for S to the nearest 0.1 degree using Equation A5. ( )       − −×− += )log()log( )(4771.2)log( 21 121 1 SS TTSTTS (A5) where: TS = critical temperature where S equals 300 MPa for the PAV conditioned RAP binder T1 = test temperature where S is closest to but greater than 300 MPa S1 = S for temperature T1, MPa T2 = test temperature where S is closest to but less than 300 kPa S2 = S for temperature T2, MPa A2.7.2. Compute the true low temperature grade for the m-value to the nearest 0.1 degree using Equation A6. ( )       − −×− += )( )(300.0 12 121 1 mm TTmTTm (A6) where: Tm = critical temperature where the m-value equals 0.300 kPa for the PAV conditioned RAP binder T1 = test temperature for the lower m-value. m1 = m-value for temperature T1 T2 = test temperature for the higher m-value. m2 = m-value for temperature T2 A2.8. Determine the performance grade for the recovered binder. A2.8.1. The critical high temperature grade for the recovered binder is the lower of the two for the as recovered (Section A2.3.1) and the RRTFOT conditions (Section A2.5.1). A2.8.2. The critical low temperature grade for the recovered binder is the higher of the two for the creep stiffness (Section A2.7.1) and the m-value (A2.7.2). A2.8.3. The critical intermediate grade for the recovered binder is the true intermediate temperature grade determined in Section A2.6.1. A3. Estimate the properties and grade of the blended binder from the properties of the recovered and virgin binders and the percentage of RAP. 173

A3.1. Determine the critical temperature of the blended binder from the high, intermediate, and low temperature test data using Equation A7: ( ))()( 100 % )()( virginTRAPTRAPBvirginTblendT Cccc −+= (A7) Where: Tc(blend) = critical temperature for the blend of RAP and new binder Tc(virgin) = critical temperature for the new binder Tc(RAP) = critical temperature for the RAP binder %RAPB = percentage of total binder content that is obtained from the RAP, wt% A3.2. The critical high temperature grade for the blended binder is the lower of the two calculated using Equation A7 for the as recovered and the RRTFOT conditions minus a factor of safety [Note A2]. A3.3. The critical low temperature grade for the blended binder is the higher of the two calculated using Equation A7 for the creep stiffness and the m-value plus a factor of safety [Note A2]. A3.4. The critical intermediate grade for the blended binder is the true intermediate temperature grade calculated using Equation A7 plus a factor of safety [Note A2]. Note A2—A factor of safety of 2°C is suggested for determining high and low critical temperatures and a factor of safety of 1°C is suggested for determining the intermediate critical temperature when grading a blended binder for an HMA mix design containing more than 15% RAP. The factor of safety provides for errors in the grading procedure. A4. Estimation of the Required Virgin Binder Properties from the specified Blended Binder Grade and RAP Content A4.1. Determine the critical temperature of the virgin asphalt binder from high, intermediate, and low temperature test data using Equation A8: ( )       − − = 100 % 1 )( 100 % )( )( RAPB RAPTRAPBspecT virginT cc c (A8) where: Tc(spec) = design critical temperature 174

= critical temperature to meet performance grade requirements ± factor of safety [Note A3] Tc(virgin) = critical temperature for the new binder Tc(RAP) = critical temperature for the RAP binder %RAPB = percentage of total binder content that is RAP, wt% Note A3—The suggested factor of safety is +2°C for the critical high temperature, −2°C for the critical low temperature, and −1°C for critical intermediate temperature. The factor of safety provides for errors in the grading procedure. A4.2. The critical high temperature grade for the virgin binder is the lower of the two calculated using Equation A8 for the as recovered and the RRTFOT conditions. A4.4. The critical low temperature grade for the virgin binder is the higher of the two calculated using Equation A8 for the creep stiffness and the m-value. A4.5. The critical intermediate grade for the virgin binder is the true intermediate temperature grade calculated using Equation A8. A5. Determine the percentage of RAP from required blended binder grade and virgin binder properties. A5.1. Determine the percentage of RAP based upon the high, intermediate and low temperature test data using equation A9: %100 )()( )()( % ×      − − = virginTRAPT virginTspecTRAPB cc cc (A9) where: Tc(spec) = design critical temperature = critical temperature to meet performance grade requirements ± factor of safety [Note A4] Tc(virgin) = critical temperature for the new binder Tc(RAP) = critical temperature for the RAP binder %RAPB = percentage of total binder content that is RAP, wt% Note A4—Care must be used in applying Equation A9. If the virgin binder meets the required critical temperature (Tc(spec)), but the RAP binder does not, the value given by Equation A9 represents a maximum allowable RAP content. If the RAP binder meets the required critical temperature, but the virgin binder does not, the values given by Equation A9 represents a minimum required RAP content. If both the virgin and RAP binders exceed the required critical temperature, then the maximum allowable RAP based on that critical temperature is 100%. If both the 175

virgin and RAP binders fail to meet the required critical temperature, then no combination of these binders will satisfy the given grading requirement. Note A5—Regardless of the results of the binder grading analysis, the RAP content of HMA mixtures shall not exceed 50%. 176