Supporting Materials for NCHRP Report 673 (2011)

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Recommended Standard Practice for Volumetric Mix Design of Dense-Graded HMA NCHRP Project 9-33 Designation M 2 1. SCOPE 1.1. This standard for mix design evaluation uses aggregate and mixture properties to produce a hot mix asphalt (HMA) job mix formula. The mix design is based on the volumetric properties of the HMA in terms of the air voids (Va), voids in the mineral aggregate (VMA), and voids filled with asphalt (VFA). 1.2. This standard may also be used to provide a preliminary selection of mix parameters as a starting point for mix evaluation and performance prediction analyses that primarily use T 320 and T 322. 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  R 30, Mixture Conditioning of Hot-Mix Asphalt (HMA)  T 2, Sampling of Aggregates  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 84, Specific Gravity and Absorption of Fine Aggregate  T 85, Specific Gravity and Absorption of Coarse Aggregate  T 100, Specific Gravity of Soils  T 164, Quantitative Extraction of Bitumen from Bituminous Paving Mixtures  T 166, Bulk Specific Gravity of Compacted Asphalt Mixtures Using Saturated Surface-Dry Specimens  T 209, Theoretical Maximum Specific Gravity and Density of Bituminous Paving Mixtures  T 228, Specific Gravity of Semi-Solid Bituminous Materials  T 240, Effect of Heat and Air on a Moving Film of Asphalt (Rolling Thin- Film Oven Test)  T 248, Reducing Samples of Aggregate to Testing Size 177

 T 275, Bulk Specific Gravity of Compacted Bituminous Mixtures Using Paraffin-Coated Specimens  T 283, Resistance of compacted Asphalt Mixtures to Moisture-Induced Damage  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 320, Determining the Permanent Shear Strain and Stiffness of Asphalt Mixtures Using the Superpave Shear Tester (SST)  T 324, Hamburg Wheel-Track Testing of Compacted Hot-Mix Asphalt (HMA) 2.2. Asphalt Institute Publication:  MS-2, Mix Design Methods for Asphalt Concrete and Other Mix Types 2.3. National Asphalt Pavement Association Publication  IS 128, HMA Pavement Mix Type Selection Guide 2.4. Other References:  NCHRP M 1, Recommended Standard Specification for Design of Dense- Graded HMA  NCHRP Report 508—Accelerated Laboratory Rutting Tests: Evaluation of the Asphalt Pavement Analyzer, A. Cooley, Transportation Research Board, Washington, DC, 2003.  NCHRP Report 629, Ruggedness Testing of the Dynamic Modulus and Flow Number Tests with the Simple Performance Tester, R. Bonaquist, Transportation Research Board, Washington, DC, 2008.  LTPP Seasonal Asphalt Concrete Pavement Temperature Models. FHWA- RD-97-103, FHWA, U.S. Department of Transportation, Washington, DC, September 1988. 3. TERMINOLOGY 3.1. HMA—hot mix asphalt 3.2. design ESALs—Design equivalent (80 kN) single axle loads. 3.2.1. Discussion—design ESALs are the anticipated project traffic level expected on the design lane over the design life of the pavement. 178

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—As 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 binder absorbed into the aggregate (equal to the difference in aggregate volume when calculated with the bulk specific gravity and effective specific gravity). 3.6. binder content (Pb)—The percent by mass of binder in the total mixture including binder and aggregate. 3.7. effective binder volume (Vbe)—The volume of binder which is not absorbed into the aggregate. 3.8. voids filled with asphalt (VFA)—the percentage of the VMA filled with binder (the effective binder volume divided by the VMA). 3.9. dust-to-binder ratio (P0.075/Pbe)—By mass, the ratio between the percent of aggregate passing the 75-µm (No. 200) sieve (P0.75) and the effective binder content (Pbe). 3.10. nominal maximum aggregate size—One size larger than the first sieve that retains more than 10 percent aggregate (Note 2). 3.11. maximum aggregate size—One size larger than the nominal maximum aggregate size (Note 2). Note 2—The definitions given in Sections 3.10 and 3.11 also apply to Superpave mixes, but differ from the definitions published in other AASHTO standards. 3.12. reclaimed asphalt pavement (RAP)—Pavement materials, removed, processed, or both, containing asphalt binder and aggregate. 3.13. primary control sieve (PCS)—the sieve defining the break point between fine- and coarse-graded mixtures for each nominal maximum aggregate size. 3.14. compositional requirement—specified requirements on aggregate quality and mixture composition, including coarse aggregate crush count, flat and elongated 179

particles, fine aggregate angularity, clay content/sand equivalent, VMA, air voids, and dust:binder ratio. 4. SUMMARY OF THE PRACTICE 4.1. Gather Information—All pertinent information concerning the paving project and mix design are gathered and organized. This should include information on potential binders, aggregates, and RAP stockpiles 4.2. Select Asphalt Binder—An asphalt binder meeting the performance grading requirements as specified in NCHRP 9-33 M 1 is selected. 4.3. Determine Compaction Level—Based upon anticipated traffic level, the number of design gyrations is selected. 4.4. Select Nominal Maximum Aggregate Size—The nominal maximum aggregate size (NMAS) is usually specified by the agency, and depends on the lift thickness to be used in the paving project. 4.5. Determine Target VMA and Air Voids Value—Target VMA increases one percent for every size increase in NMAS, but may be increased up to 1.0% at the agency’s discretion. The target air voids value is usually specified at 4.0%, but may vary from 3.5 to 4.5%. 4.6. Calculate Target Binder Content—The target effect binder volume (Vbe) is the target VMA minus the target air voids value. 4.7. Calculate Aggregate Volume—The aggregate volume is calculated as 100% minus VMA. 4.8. Proportion Aggregate Blends for Trial Mixtures—Aggregate and RAP stockpiles are selected, based on NMAS, available materials and the values of specified properties. Aggregate properties specified by the agency but not addressed in this standard must also be considered. Prepare aggregate blends for three trial mixtures by proportioning selected aggregates and RAP to create coarse, dense and fine aggregate gradations, that is, near the upper specification limits, through the center of the specification limits and near the lower specification limits for the aggregate gradation. 4.9. Calculate Trial Mixture Proportions by Weight and Check Dust/Binder Ratio—The volumetric mix proportions are used to calculate mix proportions by weight and batch weights for trial mixes. 4.10. Evaluate and Refine Trial Mixtures—For each trial mixture, specimens are prepared using the Superpave gyratory compactor, and their bulk specific 180

gravity determined, along with the theoretical maximum specific gravity of the loose mixture. From these data, VMA, air voids and dust to binder ratio are calculated and evaluated to determine if they meet the specified compositional requirements. If one of the trial mixtures meets all compositional requirements it is selected for performance evaluation. If none of the trial mixtures meets all compositional requirements, then additional trial mixtures are prepared and evaluated until a mixture meeting all established compositional requirements has been developed. 4.11. Evaluate Performance—The moisture resistance of the selected trial mixture is evaluated in accordance with AASHTO T 283. If necessary, the mix design is modified to meet the requirements of AASHTO T 283. The rut resistance of the trial mixture is then evaluated using one of six test methods. The mix design is modified as needed until rut resistance requirements are met. 4.12. Compile Mix Design Report—A clear and concise report documenting project information, the composition of the final mix design, and the values of all specified properties is prepared. 4. SIGNIFICANCE AND USE 4.1. This standard may be used to select and evaluate materials for dense-graded HMA volumetric mix designs. 5. GATHER INFORMATION 5.1. All pertinent information concerning the paving project and mix design shall be gathered and compiled. This includes the name or code identifying the paving project, the location, the lift thickness or NMAS specified by the agency, the design traffic level, the design life of the pavement, the VMA and air voids if specified by the agency, the binder performance grade if specified by the agency, and other agency-specified properties not addressed in this specification. 5.2. A list of available materials should be compiled, including available aggregates and their specification properties, RAP stockpiles and their specification properties, and asphalt binders and their specification properties. 181

6. SELECT ASPHALT BINDER 6.1. In many cases, the agency will specify the binder performance grade to be used in the mix design for the paving project. If not, select an asphalt binder meeting the requirements of NCHRP 9-33 M 1. If RAP materials are being used, and the total RAP content of the mix exceeds 15% by weight, the performance grade of the blended binder—new binder plus RAP binder—must meet the specified requirements. Procedures for determining blended binder grades for HMA mix designs containing RAP are given in NCHRP 9-33 M 1. 7. DETERMINE COMPACTION LEVEL 7.1. The number of design gyrations for the mix design shall be as specified in Table 1. Table 1 – Gyratory Compaction Effort for Dense-Graded HMA Mixtures Design ESALs (millions) Ndesign Typical Roadway a < 0.3 50 Applications include roadways with very light traffic volumes such as local roads, country roads, and city streets where truck traffic is prohibited or at a very minimal level. Traffic on these roadways would be considered local in nature, not regional, intrastate, or interstate. Special purpose roadways serving recreational sites or areas may also be applicable to this level. 0.3 to < 3 75 Applications include many collector roads or access streets. Medium-trafficked city streets and the majority of country roadways may be applicable to this level. 3 to < 30 100 Applications include many two-lane, multilane, divided, and partially or completely controlled access roadways. Among these are medium to highly trafficked city streets, many state routes, U.S. highways, and some rural Interstates. > 30 125 Applications include the vast majority of the U.S. Interstate System, both rural and urban in nature. Special applications such as truck-weighing stations or truck-climbing lanes on two-lane roadways may also be applicable to this level. aAs defined in A Policy on Geometric Design of Highways and Streets, 2004, AASHTO. Note 2 – When specified by the agency and the top of the design layer is > 100 mm from the pavement surface and the estimated design traffic level is > 0.3 million ESALs, decrease the estimated design traffic level by one, unless the mixture will be exposed to significant mainline construction traffic prior to being overlaid. If 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 the mixture design purposes. 182

Note 3 – When it is estimated that the design traffic level is between 3 and <10 million ESALs, the Agency may, at its discretion, specify Ndesign at 75. 8. SELECT NOMINAL MAXIMUM AGGREGATE SIZE 8.1. The NMAS for the mix design is usually specified by the agency. 8.2. In cased where the NMAS has not been specified by the agency, select the NMAS following the guidelines given in Table 2. Table 2—Recommended Aggregate NMAS for Different Applications and Lift Thicknesses 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 9. DETERMINE TARGET VMA AND AIR VOIDS VALUES 9.1. Select the target VMA for the mix design. The target VMA shall be between the minimum and maximum values specified in Table 3, and should preferably be in the center of the specified range. 9.2. Select the target air void content for the mix design. The target air void content shall be between 3.5 and 4.5%, and should preferably be set at 4.0%. 183

Table 3—VMA Values for Dense-Graded HMA 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. 10. CALCULATE TARGET BINDER CONTENT 10.1. The target binder content, expressed as a volume (Vb) is calculated as the target VMA minus the target air voids, plus 1.0% to account for absorption of binder by the aggregate. 10.2. If desired, a more accurate estimate of the effect of absorption can be used in calculating total binder content based upon the water absorption of the aggregate. Using this approach, the target binder content is calculated using Equation 1:             −+= 2100 1 wasbb PGVMAVBEV (1) Where: Vb = total asphalt content by volume% VBE = effective asphalt content by volume% VMA = voids in the mineral aggregate = Vbe + air void content Gsb = aggregate bulk specific gravity Pwa = water absorption of the aggregate, weight% 11. CALCULATE AGGREGATE VOLUME 11.1 The total aggregate volume percentage is calculated as 100% minus the target VMA. 184

12. PROPORTION AGGREGATE BLENDS FOR TRIAL MIXTURES 12.1. Select aggregates and RAP materials (if applicable) that will be used for the mix design. 12.1.1. The aggregates and RAP materials shall conform to the NMAS selected for the mix design. 12.1.2. The aggregates and RAP materials shall be selected so that the final aggregate blend will likely pass aggregate requirements specified in NCHRP 9-33 M 1, and any other applicable requirements specified by the agency. Note 5—Initial conformance to aggregate specifications is normally estimated based upon the properties of individual aggregates and RAP materials and the composition of the aggregate blend. Final conformance must be based on actual measurement of the final aggregate blend. Note 6—RAP aggregates need not meet clay content (sand equivalent) requirements. 12.2. Characterize the properties of the aggregates. 12.2.1. Obtain samples of aggregates to be used for the mix design from the aggregate stockpiles in accordance with AASHTO T 2. 12.2.2. Reduce the samples of aggregate according to AASHTO T 248 to sizes meeting the requirements specified in AASHTO T 27. 12.2.3. Wash and grade each aggregate according to the procedures given in AASHTO T 11 and AASHTO T 27. 12.2.4. Determine the bulk and apparent specific gravity for each coarse and fine aggregate in accordance with AASHTO T 85 and AASHTO T 84, respectively, and determine the specific gravity of the mineral filler in accordance with AASHTO T 100. 12.3. Characterize the RAP materials, if applicable, following the procedures given in Appendix A. This will include determination of the binder content, the aggregate gradation, the RAP aggregate bulk and apparent specific gravity, the RAP aggregate specification properties (not including clay content/sand equivalent, which does not apply), and the RAP binder grade. The RAP characterization should also include an estimate of the maximum amount of RAP that can be used in the mix design without increasing the production variability of the final mix to an unacceptable level. 185

Note 7—It is recommended that the field compaction temperature be greater than the as-recovered high temperature grade of the RAP binder. If the total time that the HMA will remain at a temperature above the as-recovered high temperature grade of the RAP binder is expected to be less than 2 hours, it is recommended that a plant mixing study be conducted to ensure that the RAP binder and new binder adequately mix. Note 8—In most cases, the ignition oven, AASHTO T 308, can be used to obtain the representative sample of RAP aggregate for consensus property testing. 12.4. Determine the proportions of the aggregate blends for up to three initial trial mixtures. Note 9—For mix designs using new materials, or that differ substantially in volumetric composition from existing mix designs, three trial mixtures should initially be prepared. If an existing mix design is being refined with only minor changes in materials, composition, or both, only one or two initial trial mixtures may be necessary. 12.4.1. Determining aggregate proportions for an aggregate blend for a trial mix is largely a trial-and-error procedure. Initial proportions are assumed for each aggregate in a blend and the resulting gradation is calculated and compared to the desired gradation. If it is close to the target gradation, the proportions are used for the trial mixture. If not, the proportions are altered until an acceptable gradation is produced. Note 10—For new mix designs involving three initial trial mixtures, one trial mixture should be towards the upper limits of the gradation band given in NCHRP 9-33 M 1 (“fine” gradation),one should be near the lower limit (“coarse” gradation), and one should be near the center of the gradation band (“dense” gradation). When modifying existing mix designs, experience is the best guide in developing aggregate blends for one or two initial trial mixtures. 12.4.2. Calculate the percent passing for each aggregate blend using Equation 2: P = (PmA × a) + (PmB × b) + (PmC × c) +… (2) Where: Pm = Percentage of aggregate passing sieve size m for the combined blend of aggregates A, B, C, etc. PmA = Percentage of material passing sieve size m for aggregate A a = Fraction of aggregate A in combined aggregate blend PmB = Percentage of material passing sieve size m for aggregate B b = Fraction of aggregate B in combined aggregate blend PmC = Percentage of material passing sieve size m for aggregate C 186

c = Fraction of aggregate C in combined aggregate blend 12.4.3. Compare the gradations of the aggregate trial blends with the gradation control points given in NCHRP 9-33 M 1, and verify that the gradations meet or nearly meet these limits. Note 11—Other than the requirements for NMAS, the aggregate gradations described in NCHRP 9-33 M 1 should be considered guidelines and not requirements. If necessary, aggregate blends may deviate from the control points given in NCHRP 9-33 M 1, except for the control points defining the NMAS. Also, the requirements for dust to binder ratio given in NCHRP 9-33 M 1 must be met. Note 12—If desired, the specification properties of the aggregate blends can be estimated from the blend proportions and the properties of the individual aggregates and RAP materials, to verify that they will likely meet the requirements of NCHRP 9-33 M 1. 13. CALCULATE TRIAL MIXTURE PROPORTIONS BY WEIGHT AND CHECK DUST/BINDER RATIO 13.1. Calculate the overall aggregate bulk specific gravity using Equation 3:   +      +      +      +++ = 3 /3 2 /2 1 /1 /3/2/1 sb As sb As sb As AsAsAs sb G P G P G P PPPG (3) Where: Gsb = overall bulk specific gravity for aggregate blend Ps1/A = volume% of aggregate 1 in aggregate blend Gsb1 = bulk specific gravity for aggregate 1 Ps2/A = volume% of aggregate 2 in aggregate blend Gsb2 = bulk specific gravity for aggregate 2 Ps3/A = volume% of aggregate 3 in aggregate blend Gsb3 = bulk specific gravity for aggregate 3 13.2. Calculate the asphalt binder content by weight using Equation 4: %100× + = bbsbsb bb b GVGV GVP (4) 187

Where: Pb = total binder content,% by total mix weight Vb = total binder content,% by total mix volume Gb = binder specific gravity Vsb = aggregate content,% by total mix volume Gsb = overall bulk specific gravity of aggregate (Equation 3) 13.3. Estimate the effective asphalt binder content by weight using Equation 5: %100× + = bbsbsb bbe be GVGV GVP (5) Where: Pbe = effective binder content,% by total mix weight Vbe = effective binder content,% by total mix volume Gb = binder specific gravity Vsb = aggregate content,% by total mix volume Gsb = overall bulk specific gravity of aggregate (Equation 3) 13.4. Calculate the aggregate content using Equation 6: %100× + = bbsbsb sbsb s GVGV GVP (6) Where: Pb = total aggregate content,% by total mix weight Vb = total binder content,% by total mix volume Gb = binder specific gravity Vsb = aggregate content,% by total mix volume Gsb = overall bulk specific gravity of aggregate (Equation 3) 13.5. Calculate the weight percentage of each aggregate using Equation 7:      = 100 /1 1 As ss PPP (7) Where: Ps1 = weight percent (by total mix) of aggregate 1 (or aggregate 2, 3, etc.) 188

Ps = weight percent (by total mix) of combined aggregate, from Equation 7 Ps1/A = weight percent (in aggregate blend) of aggregate 1 (or aggregate 2, 3, etc.) 13.6. Estimate the percent of mineral dust (material finer than 0.075 mm) in the total mixture using Equation 8: 100 33/075.022/075.011/075.0 075.0 +++ = ssssss PPPPPPP (8) Where: P0.075 = mineral dust content (material finer than 0.075 mm), percent by total mix weight P0.075/s1 =% passing the 0.075 mm sieve for aggregate 1 Ps1 = weight percent (by total mix) of aggregate 1 P0.075/s2 =% passing the 0.075 mm sieve for aggregate 2 Ps2 = weight percent (by total mix) of aggregate 2 P0.075/s3 =% passing the 0.075 mm sieve for aggregate 3 Ps3 = weight percent (by total mix) of aggregate 3 13.7. Estimate the dust to binder ratio using Equation 9: beP PBD 075.0/ = (9) Where: D/B = dust to binder ratio, calculated using effective binder content P0.075 = mineral dust content,% by total mix weight (Equation 8) Pbe = effective binder content,% by total mix weight (Equation 5) 13.7.1. Verify that the dust to binder ratio meets the requirements of NCHRP 9-33 M 1. 14. EVALUATE AND REFINE TRIAL MIXTURES 14.1. Prepare replicate specimens for specific gravity measurements for each trial mixture. Note 13—At least two replicate specimens are required, but three or more may be prepared if desired. Generally, 4500 to 4700 g of aggregate are sufficient for each compacted gyratory specimen having a height of 110 to 120 mm, for aggregate having bulk specific gravity values from 2.55 to 2.70. 189

14.1.1 Determine batch weights for each trial mixture by multiplying the total mix weight by the weight fraction of each component (weight percentage divided by 100%). 14.1.2. Weight out aggregates for each batch, taking care to avoid segregation while handling the aggregates. This may require sieving coarse aggregates into different size fractions and weighing out these fractions separately. 14.1.3. Condition the mixture in accordance with R 30, and compact specimens using the Superpave gyratory compactor in accordance with T 312, with the number of gyrations determined as described in Section 7. 14.2. Determine the bulk specific gravity (Gmb) of each of the compacted specimens in accordance with AASHTO T 166 or AASHTO T 275 as appropriate. 14.3. Determine the air void content and VMA of the specimens. 14.3.1. Calculation the air void content of each compacted specimen using Equation 10:             −= mm mb a G GV 1100 (10) Where: Va = Air void content, volume% Gmb = Bulk specific gravity of compacted mixture Gmm = Maximum theoretical specific gravity of loose mixture 14.3.2. Calculate the effective asphalt content of each compacted specimen using Equation 11:             −      +      −= mmsb s b b mbbbe GG P G PGVV 100 (11) Where: Vbe = Effective binder content, percent by total mixture volume Vb = Total binder content, percent by total mixture volume Gmb = Bulk specific gravity of the mixture Pb = Total asphalt binder content,% by mix mass Gb = Specific gravity of the asphalt binder Ps = Total aggregate content,% by mix mass = 100 − Pb Gsb = Average bulk specific gravity for the aggregate blend Gmm = Maximum specific gravity of the mixture 190

14.3.3. Calculate the VMA using Equation 12: VMA = Va + Vbe (12) Where: VMA = Voids in mineral aggregate, percent by total mixture volume Va = Air void content Vbe = Effective binder content, percent by total mixture volume 14.4. Tabulate all specified properties for trial mixtures and compare to required values. Select as the final mix design the trial mixture that meets all requirements with the property values most nearly in the center of the specified ranges. Proceed to performance evaluation as described in 14.6. 14.5. If none of the trial mixtures meet all requirements, additional trial mixtures must be prepared and evaluated. Proportion aggregate blends for additional trial mixtures based upon the properties of initial trial mixtures. Note 14—Evaluating and refining trial mixtures when developing an HMA mix design is largely a trial-and-error process. Judgment and experience are an important part of this process. Additional useful information concerning developing and adjusting aggregate blends for HMA trial mixtures can be found in the Asphalt Institute’s MS-2, Transportation Research Circular E-C044: Bailey Method for Gradation Selection in Hot-Mix Asphalt Mixture Design. and Mix Design Manual for Hot-Mix Asphalt, developed during NCHRP Project 9-33. 14.5.1. Prepare specimens from additional trial mixtures and determine the bulk and theoretical maximum specific gravity values. Calculate air voids, VMA, dust to binder ratio and other specified properties to determine if any of the additional trial mixtures meet all requirements. If not, continue to modify the aggregate blends for trial mixtures, prepare specimens, and evaluate specified properties, until a suitable mix design has been developed. Proceed to performance evaluation of the final mix design as described in 15. 191

15. EVALUATE PERFORMANCE OF THE MIX DESIGN. 15.1. Evaluate the moisture resistance of the final mix design. 15.1.2. Using the final mix design, prepare six mixture specimens (nine are needed if freeze-thaw testing is required). Condition the mixture in accordance with AASHTO R 30, and compact the specimens to 7.0 ± 0.5 percent air voids in accordance with AASHTO T 312. 15.1.3. Test the specimens and calculate the tensile strength ratio in accordance with AASHTO T 283. 15.1.4. If the tensile strength ratio is less than 0.80, adjust the mix design to increase the moisture resistance of the mix to an acceptable level as measured using AASHTO T 283. Such adjustments might include adding hydrated lime to the mixture, adding various anti-strip additives, or changing the source of the aggregate binder, or both. Once the required tensile strength ratio of 0.80 is achieved (along with all other specified requirements), proceed to rut resistance evaluation. 15.2. Evaluate the rut resistance of the final mix design. 15.2.1. Select the test to be used in evaluating rut resistance. Allowable procedures are the asphalt mixture performance tester (AMPT), using either the flow number test (14.6.2.3) or the flow time test (14.6.2.4); the asphalt pavement analyzer (APA, 14.6.2.5); the Hamburg wheel tracking test (HWTT, 14.6.2.6); the Superpave shear tester, repeated shear at constant height (SST/RSCH) test (14.6.2.7); or the high temperature indirect tensile (HT/IDT) strength test (14.6.2.8). 15.2.2. Using the final mix design, prepare the required number and type of specimens for the selected rut resistance test. Condition the mixtures in accordance with R 30. 15.2.3. For AMPT testing using the flow number procedure, follow procedures given in NCHRP Report 629, Ruggedness Testing of the Dynamic Modulus and Flow Number Tests with the Simple Performance Tester. Prepare two specimens in accordance with AASHTO T 312, with a final air void content within 0.5 percent of the expected as-constructed air void content. If the as-constructed air void content is not specified, compact the specimens to an air void content of 7.0 ± 0.5%. Final nominal specimen dimensions are 150 mm high by 100 mm in diameter. For mixtures designed for fast traffic (≥ 70 kph), the test temperature shall be the average, 7-day maximum pavement temperature 20 mm from the surface, at 50% reliability as determined using LTPPBind version 3.1. For slow traffic (25 to < 70 kph), the test temperature shall be 6°C higher than the test temperature for fast traffic; for very slow traffic (< 25 kph), the test temperature shall be 12°C higher. In all cases, the test temperature shall be controlled to within 0.5°C of that specified. Perform the flow number test and report the 192

average of the results for the two specimens tested. The recommended minimum flow number values as a function of design traffic level are shown in Table 4 (Note 15). If the required minimum flow number value is not met, the mix must be modified to improve rut resistance, while meeting all other applicable requirements as given in this standard (Note 16). Table 4—Recommended Minimum Flow Number Requirements Traffic Level Million ESALs Minimum Flow Number Cycles < 3 --- 3 to < 10 340 10 to < 30 560 ≥ 30 890 Note 15—The minimum flow number values, and other recommended test values for rut resistance tests given in this standard, should be considered guidelines that should be evaluated and modified as necessary by the agency to account for local materials, climate and traffic conditions. Note 16—Rut resistance of HMA mixtures can be improved by a variety of methods: increasing the high temperature binder grade; using a polymer modified binder if not already in use; by using aggregate with increased angularity, hardness, or both; or by a combination of these methods. 15.2.4. For AMPT testing using the flow time procedure, follow procedures given in NCHRP Report 629, Ruggedness Testing of the Dynamic Modulus and Flow Number Tests with the Simple Performance Tester. Prepare two specimens in accordance with T 312, with a final air void content within 0.5 percent of the expected as-constructed air void content. If the as-constructed air void content is not specified, compact the specimens to an air void content of 7.0 ± 0.5%. Final nominal specimen dimensions are 150 mm high by 100 mm in diameter. For mixtures designed for fast traffic (≥ 70 kph), the test temperature shall be the average, 7-day maximum pavement temperature 20 mm from the surface, at 50% reliability as determined using LTPPBind version 3.1. For slow traffic (25 to < 70 kph), the test temperature shall be 6°C higher than the test temperature for fast traffic; for very slow traffic (< 25 kph), the test temperature shall be 12°C higher. In all cases the test temperature shall be controlled to within 0.5°C of that specified. Perform the flow time test and report the average of the results for the two specimens tested. The recommended minimum flow time values as a function of design traffic level are shown in Table 5 (Note 15). If the required minimum flow time value is not met, the mix must be modified to improve rut resistance, while meeting all other applicable requirements as given in this standard (Note 16). 193

Table 5—Recommended Minimum Flow Time Requirements Traffic Level Million ESALs Minimum Flow Time s < 3 --- 3 to < 10 110 10 to < 30 180 ≥ 30 290 15.2.5. For rut resistance testing using the APA device, follow procedures given in Appendix B of NCHRP Report 508—Accelerated Laboratory Rutting Tests: Evaluation of the Asphalt Pavement Analyzer. Prepare six specimens in accordance with AASHTO T 312, with a final air void content of 4.0 ± 0.5%. Final nominal specimen dimensions are 150 mm high by 75 mm in diameter. The test temperature shall be the temperature corresponding to the high-temperature binder performance grade specified for the project by the agency. Perform the APA test and report the average of the results for the six specimens tested, as described in Appendix B of NCHRP Report 508. The recommended maximum rut depth values as a function of design traffic level are shown in Table 6 (Note 15). If the maximum rut depth value is exceeded, the mix must be modified to improve rut resistance, while meeting all other applicable requirements as given in this standard (Note 16). Table 6—Recommended Maximum Rut Depths for the APA Test. Traffic Level Million ESALs Maximum Rut Depth mm < 3 --- 3 to < 10 5 10 to < 30 4 ≥ 30 3 - 15.2.6. For rut resistance testing using the Hamburg wheel tracking test, follow procedures given in AASHTO T 324. Prepare two specimens in accordance with T 312, with a final air void content of 7.0 ± 2.0%. Final nominal specimen dimensions are 150 mm high by 75 mm in diameter. The test temperature shall be 40 ± 1°C for mixtures made with non-modified binders having a high temperature grade of PG 64 or less, and 50 ± 1°C for mixtures made with binders having a high temperature grade above PG 64. The wheel load shall be 705 ± 2 N. Perform the Hamburg wheel tracking test under wet conditions and report the average of the results for the two specimens tested, as wheel passes to a 12-mm rut depth. The recommended minimum values as a function of design traffic level are shown in Table 7 (Note 15). If the number of passes does not meet the required value, the mix must be modified to improve rut resistance, while meeting all other applicable requirements as given in this standard (Note 16). 194

Table 7—Recommended Minimum Passes to a 12-mm Rut Depth for Hamburg Wheel Tracking Test High Temperature Binder Grade Minimum Passes to 12-mm Rut Depth PG 64 or lower 10,000 PG 70 15,000 PG 76 or higher 20,000 15.2.7. For rut resistance testing using the SST/RSCH test, follow procedures given in AASHTO T 320 for the repeated shear at constant height test (Note 17). Prepare two specimens in accordance with AASHTO T 312, with a final air void content of 3.0 ± 0.5%. Prepare specimens as described in T 320. For mixtures designed for fast traffic (≥ 70 kph), the test temperature shall be the average, 7-day maximum pavement temperature 20 mm from the surface, at 50% reliability as determined using LTPPBind version 3.1. For slow traffic (25 to < 70 kph), the test temperature shall be 6°C higher than the test temperature for fast traffic; for very slow traffic (< 25 kph), the test temperature shall be 12°C higher. Perform the SST/RSCH test and report the average of the results for the two specimens tested. The recommended maximum values for permanent shear strain (MPSS) as a function of design traffic level are shown in Table 8 (Note 15). If the required MPSS value is exceeded, the mix must be modified to improve rut resistance, while meeting all other applicable requirements as given in this standard (Note 16). Table 8—Recommended Maximum Values for MPSS Determined Using the SST/RSCH Test Traffic Level Million ESALs Maximum Value for MPSS % < 3 --- 3 to < 10 3.2 10 to < 30 2.2 ≥ 30 1.4 Note 17—Due to the cost and complexity of the SST, the SST/RSCH test procedure is not recommended for routine use by most pavements and materials testing laboratories. The procedure has been included in this standard so that research laboratories that have the SST and have significant experience with it can use it as an acceptable method for evaluating rut resistance in the design of HMA mixtures. 195

15.2.8. For rut resistance testing using the HT/IDT test, perform an indirect tension test according to AASHTO T 283 for unconditioned (dry) laboratory-prepared, laboratory compacted specimens, but with the following exceptions. The specimen size shall be 100 ± 10 mm high, and 150-mm in diameter. For mixtures designed for fast traffic (≥ 70 kph), the test temperature (the conditioning temperature immediately prior to testing) shall be 10°C lower than the average, 7- day maximum pavement temperature 20 mm from the surface, at 50% reliability as determined using LTPPBind version 3.1. In all cases, the test conditioning temperature shall be controlled to within 0.5°C of that specified. For slow traffic (25 to < 70 kph), the test temperature shall be 6°C higher than the test temperature for fast traffic; for very slow traffic (< 25 kph), the test temperature shall be 12°C higher. Perform the HT/IDT test and report the average of the results for the two specimens tested. The recommended minimum indirect tensile strengths as a function of design traffic level are shown in Table 9 (Note 15). If the required strength is not met, the mix must be modified to improve rut resistance, while meeting all other applicable requirements as given in this standard (Note 16). Table 9—Recommended Minimum High-Temperature Indirect Tensile Strength Requirements. Traffic Level Million ESALs Minimum HT/IDT Strength kPa < 3 --- 3 to < 10 200 10 to < 30 340 ≥ 30 460 16. COMPILE MIX DESIGN REPORT 16.1. Compile a report on the final mix design, summarizing all pertinent project information, information on the composition of the mix design, and all pertinent data on specification tests on the mixture. Appendix A: Recommended Procedure for Characterizing Reclaimed Asphalt Pavement Stockpiles A1. Sampling A1.1. Obtain representative samples from between 5 to 10 locations within the RAP stockpile in accordance with AASHTO T 2. Note A1—The size of each sample should be large enough to determine the properties of the RAP stockpile as described in this Appendix and to have sufficient material for subsequent mixture design and analysis work. A 5 to 7 kg 196

sample at each location is recommended for determining RAP stockpile properties. An additional 10 kg sample per mixture design is recommended at each location to provide sufficient RAP materials for mixture design and analysis. A1.2. From each sample location split a 5 to 7 kg sample in accordance with AASHTO T 248 for determining the properties of the RAP stockpile. Combine the remainder of the sample from each location for use in mixture design and analysis. Note A2—If AASHTO T 308 will be used for determining asphalt content and a reasonable estimate of the correction factor for the aggregate is not known, split approximately 7 kg samples for 5 of the 10 samples to develop corrections factors by determining asphalt contents using both AASHTO T 164 and AASHTO T 308. A1.3. From each 5 to 7 kg sample split an appropriate size sample in accordance with AASHTO T 248 for determining asphalt content and gradation in accordance with AASHTO T 308 or AASHTO T 164. The sample size will depend on the nominal maximum aggregate size of the RAP. Note A3—If correction factors will be determined using AASHTO T 164, split two samples (one for AASHTO T 308 and one for AASHTO T 164) from 5 of the 10 samples. A1.4. Combine the remainder of the stockpile property sample from each location. Then split the following representative samples in accordance with AASHTO T 248, as listed in Table A1: 197

Table A1—Sample Sizes for RAP Testing Purpose Approximate Size RAP Binder Properties 2.5 kg RAP Aggregate Properties 5.0 kg RAP Aggregate Specific Gravity Using Effective Specific Gravity 0.5 to 4 kg depending on the maximum particle size A2. Binder Content and Gradation A2.1. Determine the binder content of the RAP at each sampling location in accordance with AASHTO T 308 or AASHTO T 164. Note A4—If reasonable estimates of the ignition oven correction factor can be made, use AASHTO T 308. If the correction factors for local aggregate are highly variable use AASHTO T 164 or determine correction factors by testing 5 of the 10 samples using both AASHTO T 164 and AASHTO T 308. A2.2. Determine the gradation of the RAP aggregate in accordance with AASHTO T 30. A2.3. Determine the average and standard deviation of the binder content and percent passing each sieve size. A2.4. Estimate the maximum RAP content that can be used based on variability from Figures A1 through A4 (Note A5). Note A5—Other statistically based methods of variability analysis may be used to estimate the amount of RAP that can be used in an HMA mix design without causing an unacceptable increase in production variability. The general approach in any method used should be to maintain final variability in aggregate gradation and binder content significantly below maximum variability in HMA production as recommended by AASHTO, ASTM, or the agency. 198

A2.4.1. For mix designs using a single RAP stockpile or blends of stockpiles in which one of the RAP stockpiles makes up more than 70% of the RAP blend, determine the maximum amount of RAP that can be used based on aggregate gradation variability from Figure A1, by entering the chart on the horizontal axis with the standard deviation for percent passing for a given sieve size and reading the maximum RAP content on the vertical axis; repeat for each sieve size in the gradation. Also determine the maximum amount of RAP that can be used based on binder content variability from Figure A2, by entering the chart with standard deviation for binder content and reading the maximum RAP content on the vertical axis. The final maximum RAP content that can be used in the mix design based on RAP variability is the lowest maximum RAP content among the values determined for all sieve sizes and the binder content, but in no case shall exceed 50% (Note A6). Note A6—Figures A1 through A4 are based on standard deviations calculated for N=5 RAP samples taken from widely separated locations within the RAP stockpile. These figures are not valid for sample sizes below N = 5. Using standard deviations calculated from a sample size greater than N = 5 is not recommended for these charts. However, other methods of estimating maximum RAP contents for HMA mix designs based on variability will often provide more accurate results and, in general, higher RAP contents when larger samples sizes are used. A2.4.2. For mix designs using a blend of RAP stockpiles in which none of the RAP stockpiles makes up more than 70% of the RAP blend, determine the maximum amount of RAP that can be used based on aggregate gradation variability from Figure A3, by entering the chart on the horizontal axis with the standard deviation for percent passing for a given sieve size and reading the maximum RAP content on the vertical axis; repeat for each sieve size in each of the RAP aggregate gradations. Also determine the maximum amount of RAP that can be used based on binder content variability from Figure A2, by entering the chart with standard deviation for binder content and reading the maximum RAP content on the vertical axis for each of the RAP stockpiles in the blend. The final maximum RAP content that can be used in the mix design based on RAP variability is the lowest maximum RAP content among the values determined for all sieve sizes for all RAP stockpiles and for binder contents for all RAP stockpiles in the blend, but in no case shall exceed 50% (Note A6). 199

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 C on te nt , W t. % S ieve size, mm: 0.075 0. 150 0. 300 1. 18 4. 75 > 9.5 & 0.600 & 2.36 & 9.5 Figure A1—Maximum RAP Content as a Function of Standard Deviation for Aggregate % Passing, for n = 5 Samples from a Single RAP Stockpile 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 C on te nt , W t. % Figure A2—Maximum RAP Content as a Function of Standard Deviation for Asphalt Binder Content, for n = 5 Samples from a Single RAP Stockpile 200

15 20 25 30 35 40 45 50 0 1 2 3 4 5 6 7 8 9 10 Average Standard Deviation for RAP Aggregate % Passing M ax . R A P C on te nt , W t. % S ieve size, mm: 0.075 0. 150 0. 300 1. 18 4. 75 > 9.5 & 0.600 & 2.36 & 9.5 Figure A3—Maximum RAP Content as a Function of Average Standard Deviation for Aggregate % Passing, for n = 5 Samples from a Blend of RAP Stockpiles, and No Stockpile Making up More than 70% of the RAP Blend 15 20 25 30 35 40 45 50 0.2 0.3 0.4 0.5 0.6 0.7 Average Binder Standard Deviation M ax . R A P C on te nt , W t. % Figure A4—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 201

A3. RAP Aggregate Properties A3.1. Remove the binder from the 5 kg combined sample of RAP in accordance with AASHTO T 308 to obtain a sample of the RAP aggregate for testing. A3.2. Split the RAP aggregate sample on the 4.75 mm sieve. A3.3. Determine the bulk specific gravity of the coarse fraction of the RAP aggregate in accordance with AASHTO T 85. A3.4. Determine the bulk specific gravity of the fine fraction of the RAP aggregate in accordance with AASHTO T 84. Note A7—The bulk specific gravity of the RAP aggregate may be determined without removing the RAP binder if a reasonable estimate of the binder absorption is known. See Section A3.8 for details of this optional procedure. A3.5. Determine the angularity of the coarse fraction of the RAP aggregate in accordance with ASTM D 5821. A3.6. Determine the amount of flat and elongated particles in the coarse fraction of the RAP aggregate in accordance with ASTM D 4791. A3.7. Determine the angularity of the fine fraction of the RAP aggregate in accordance with AASHTO T 304. A3.8. Alternative Method for Determining Bulk Specific Gravity of RAP Aggregate Note A8—A reasonable estimate of the binder absorption for the RAP aggregate must be known to apply this procedure. The accuracy of this approach depends on the accuracy of the estimated binder absorption. A3.8.1. Determine the maximum specific gravity of the RAP in accordance with AASHTO T 209. A3.8.2. Compute the effective specific gravity of the RAP aggregate using Equation A1. b b mm b se G P G P G − − = 100 100 (A1) where: Gse = effective specific gravity of the RAP aggregate 202

Pb = binder content of the RAP (See Section A2) Gmm = maximum specific gravity of the RAP Gb = specific gravity of the RAP binder (assumed) A3.8.3. Compute the bulk specific gravity of the combined RAP aggregate using Equation A2.         +      × = 1 100 b seba se sb G GP G G (A2) where: Gsb = bulk specific gravity of the combined RAP aggregate Gse = effective specific gravity of the RAP aggregate (Equation A1) Pba = percent absorbed binder (assumed) Gb = specific gravity of the RAP binder (assumed) A4. RAP Binder Properties A4.1. Extract and recover approximately 100 g of RAP binder in accordance with AASHTO T 164 and ASTM D 5404. A4.2. 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. A4.3. Compute the As Recovered true high temperature grade to the nearest 0.1 degree using Equation A3.       − −× += )log()log( )()log( 21 121 1cov GG TTGTT eredreas (A3) where: Tas recovered = 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 A4.4. Condition the remaining binder in accordance with AASHTO T 240. 203

A4.5. 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. A4.6. Compute the RRTFOT true high temperature grade to the nearest 0.1 degree using Equation A4. ( )       − −×− += )log()log( )(3424.0)log( 21 121 1 GG TTGTTRTFOT (A4) where: TRRTFOT = temperature where G*/sinδ equals 2.20 kPa for the RRTFOT conditioned RAP binder T1 = test temperature where G*/sinδ is closest to but above 2.20 kPa G1 = G*/sinδ for temperature T1, kPa T2 = test temperature where G*/sinδ is closest to but below 2.20 kPa G2 = G*/sinδ for temperature T2, kPa A4.7. 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. A4.8. Compute the true intermediate temperature grade to the nearest 0.1 degree using Equation A5.       − −×− += )log()log( )()6990.3)(log( 21 121 1int GG TTGTT ermediate (A5) where: Tintermediate = 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 A4.9. 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. A4.10. Compute the true low temperature grade for S to the nearest 0.1 degree using Equation A6. 204

( )       − −×− += )log()log( )(4771.2)log( 21 121 1 SS TTSTTS (A6) where: TS = temperature where S equals 300 MPa for the PAV conditioned RAP binder T1 = test temperature where S is closest to but above 300 MPa S1 = S for temperature T1, MPa T2 = test temperature where S is closest to but below 300 kPa S2 = S for temperature T2, MPa A4.11. Compute the true low temperature grade for the m-value to the nearest 0.1 degree using Equation A7. ( )       − −×− += )( )(300.0 12 121 1 mm TTmTTm (A7) where: Tm = 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 A4.12. The critical high temperature grade for blending chart analyses is the lower of the two for the as recovered (Section A4.3) and the RRTFOT condition (Section A4.6). A4.13. The critical low temperature grade for blending chart analyses is the higher of the two for the creep stiffness (Section A4.11) and the m-value (A4.12). A4.14. The critical intermediate grade for blending chart analyses is the true intermediate temperature grade determined in Section A4.9. 205