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49 Proposed Standard Practice for Preparation of Cylindrical Performance Test Specimens Using the Superpave Gyratory Compactor NCHRP 9-29: PP 01 1. SCOPE 1.1 This practice covers the use of a Superpave gyratory compactor to prepare 100 mm diameter by 150 mm tall cylindrical test specimens for use in a variety of axial compression and tension performance tests. This practice in intended for dense-, gap-, and open-graded hot mix asphalt concrete mixtures with nominal maximum aggregate sizes to 37.5 mm. 1.2 This standard may involve hazardous materials, operations, and equipment, This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this procedure to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to its use. 2. REFERENCED DOCUMENTS 2.1 AASHTO Standards T 312, Preparation and Determining the Density of Hot-Mix Asphalt (HMA) Specimens by Means of the Superpave Gyratory Compactor. R 30, Mixture Conditioning of Hot-Mix Asphalt (HMA) 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 269, Percent Air Voids in Compacted Dense and Open Bituminous Paving Mixtures. 2.1.1 ASTM Standards D 3549, Thickness or Height of Compacted Bituminous Paving Mixture Specimens.

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50 3. TERMINOLOGY 3.1 Gyratory Specimen Nominal 150 mm diameter by 170 mm high cylindrical specimen prepared in a Gyratory compactor meeting the requirements of AASHTO T 312. 3.2 Test Specimen Nominal 100 mm diameter by 150 mm high cylindrical specimen that is sawed and cored from the gyratory specimen. 3. 3 End Perpendicularity - The degree to which an end surface departs from being perpendicular to the axis of the cylindrical test specimen. This is measured using a combination square with the blade touching the cylinder parallel to its axis, and the head touching the highest point on the end of the cylinder. The distance between the head of the square and the lowest point on the end of the cylinder is measured with feeler gauges. 3.4 End Planeness Maximum departure of the specimen end from a plane. This is measured using a straight edge and feeler gauges. 4. SUMMARY OF PRACTICE 4.1 This practice presents methods for preparing 100 mm diameter by 150 mm tall cylindrical test specimens for use in a variety of axial compression and tension performance tests. 5. SIGNIFICANCE AND USE 5.1 This practice should be used to prepare specimens for the following standard tests: AASHTO TP 62, Determining Dynamic Modulus of Hot-Mix Asphalt Concrete Mixtures NCHRP 9-29 PP 03, Determining the Dynamic Modulus and Flow Number for Hot-Mix Asphalt (HMA) Using the Simple Performance Test System 5.2 This practice may also be used to prepare specimens for other non-standard tests requiring 100 mm diameter by 150 mm tall cylindrical test specimens.

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51 6. APPARATUS 6.1 Superpave Gyratory Compactor - A compactor meeting the requirements of AASHTO T 312 and capable of preparing finished 150 mm diameter specimens that a minimum of 170 mm tall. Note 1 - Research completed to date has not determined if it is critical that the compactor maintain the internal angle specified in AASHTO T 312 when compacting 170 mm tall specimens. Until additional work is completed compactors meeting either the external or internal angle requirements of AASHTO T 312 may be used. 6.2 Mixture Preparation Equipment Balances, ovens, thermometers, mixer, pans, and other miscellaneous equipment needed to prepare gyratory specimens in accordance with AASHTO T 312 and make specific gravity measurements in accordance with AASHTO T 166, T 209, and T 269. 6.3 Core Drill An air or water cooled diamond bit core drill capable of cutting nominal 100 mm diameter cores meeting the dimensional requirements of Section 9.5.3. The core drill shall be equipped with a fixture for holding 150 mm diameter gyratory specimens. Note 2 Core drills with fixed and adjustable rotational speed have been successfully used to prepare specimens meeting the dimensional tolerances given in Section 9.5.3. Rotational speeds from 450 750 RPM have been used. Note 3 Core drills with automatic and manual feed rate control have been successfully used to prepare specimens meeting the dimensional tolerances given in Section 9.5.3. 6.4 Masonry Saw An air or water cooled diamond bladed masonry saw capable of cutting specimens to a nominal length of 150 mm and meeting the tolerances for end perpendicularity and end flatness given in Section 9.5.3. Note 4 Single and double bladed saws have been successfully used to prepare specimens meeting the dimensional tolerances given in Section 9.5.3. Both types of saws require a fixture to securely hold the specimen during sawing, and control of the feed rate. Note 5 In National Cooperative Highway Research Project 9-29, a machine that performs both the sawing and coring operation within the tolerances specified in Section 9.5.3 was developed. Contact: Shedworks, Inc., 2151 Harvey Mitchell Parkway, S., Suite 320, College Station, TX 77840-5244, Phone (979) 695-8416, Fax 695-9629, email wwc@shedworks.com. 6.5 Square Combination square with a 300 mm blade and 100 mm head.

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52 6.6 Feeler Gauges Tapered leaf feeler gauges in 0.05 mm increments. 6.7 Metal Ruler Metal ruler capable of measuring nominal 150 mm long specimens to the nearest 1 mm. 6.8 Calipers Calipers capable of measuring nominal 100 mm diameter specimens to the nearest 0.1 mm. 7. HAZARDS 7.1 This practice and associated standards involve handling of hot asphalt binder, aggregates and asphalt mixtures, and the use of sawing and coring machinery. Use standard safety precautions, equipment, and clothing when handling hot materials and operating machinery. 8. STANDARDIZATION 8.1 Items associated with this practice that require calibration are included in the AASHTO Standards referenced in Section 2. Refer to the pertinent section of the referenced standards for information concerning calibration. 9. PROCEDURE 9.1 HMA Mixture Preparation 9.1.1 Prepare HMA mixture for each test specimen and a companion maximum specific gravity test in accordance with Section 8 of AASHTO T 312. 9.1.2 The mass of mixture needed for each specimen will depend on the gyratory specimen height, the specific gravity of the aggregate, the nominal maximum aggregate size and gradation (coarse or fine), and the target air void content for the test specimens. Appendix A describes a trial and error procedure developed in NCHRP Project 9-19 for determining the mass of mixture required to reach a specified test specimen target air void content for gyratory specimens prepared to a height of 170 mm. Note 6 Test specimens with acceptable properties have been prepared from gyratory specimens ranging in height from 165 to 175 mm. The height of the gyratory specimen that should be used depends on the air void gradient produced by the specific compactor, and the capabilities of the sawing equipment. 9.1.3 Perform mixture conditioning for the test specimens and companion maximum specific gravity test in accordance with Section 7.2 of AASHTO R-30, Short-Term Conditioning for Mixture Mechanical Property Testing.

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53 9.2 Gyratory Specimen Compaction 9.2.1 Compact the gyratory specimens in accordance with Section 9 of AASHTO T 312. 9.2.2 Compact the gyratory specimens to the target gyratory specimen height. Note 7 Each laboratory should determine a target gyratory specimen height based on the procedure for evaluating test specimen uniformity given in Appendix B, and an evaluation of the ability of the sawing equipment to maintain the dimensional tolerances given in Section 9.5.3. 9.3 Long-Term Conditioning (Optional) 9.3.1 If it is desired to simulate long-term aging, condition the gyratory specimen in accordance with Sections 7.3.4 through 7.3.6 of AASHTO R-30. 9.3.2 To obtain accurate volumetric measurements on the long-term conditioned specimens, also condition a companion sample of short-term conditioned loose mix meeting the sample size requirements of AASHTO T 209 in accordance with Sections 7.3.4 through 7.3.6 of AASHTO R-30. 9.4 Gyratory Specimen Density and Air Voids (Optional) 9.4.1 Determine the maximum specific gravity of the mixture in accordance with AASHTO T 209 (If long-term conditioning has been used, determine the maximum specific gravity on the long-term conditioned loose mix sample). Record the maximum specific gravity of the mixture. 9.4.2 For dense- and gap-graded mixtures, determine the bulk specific gravity of the gyratory specimen in accordance with AASHTO T 166. Record the bulk specific gravity of the gyratory specimen. 9.4.3 For open-graded mixtures, determine the bulk specific gravity of the gyratory specimen in accordance with Section 6.2 of AASHTO T 269. 9.4.4 Compute the air void content of the gyratory specimen in accordance with AASHTO T 269. Record the air void content of the gyratory specimen. Note 8 Section 9.4 is optional because acceptance of the test specimen for mechanical property testing is based on the air void content of the test specimen, not the gyratory specimen. However, monitoring gyratory specimen density can identify improperly prepared specimens early in the specimen fabrication process. Information on gyratory specimen air voids and test specimens air voids will also assist the laboratory in establishing potentially more precise methods than Appendix A for preparing test specimens to a target air void content.

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54 9.5 Test Specimen Preparation 9.5.1 Drill a nominal 100 mm diameter core from the center of the gyratory specimen. Both the gyratory specimen and the drill shall be adequately supported to ensure that the resulting core is cylindrical with sides that are smooth, parallel, and meet the tolerances on specimen diameter given in Section 9.5.3. 9.5.2 Saw the ends of the core to obtain a nominal 150 mm tall test specimen. Both the core and the saw shall be adequately supported to ensure that the resulting test specimen meets the tolerances given in Section 9.5.3 for height, end flatness and end perpendicularity. Note 9 With most equipment, it is better to perform the coring before the sawing. However, these operations may be done in either order as long as the dimensional tolerances in Section 9.5.3 are met. 9.5.3 Test specimens shall meet the dimensional tolerances given in Table 1. Table 1. Test Specimen Dimensional Tolerances. Item Specification Method Average Diameter 100 mm to 104 mm 9.5.3.1 Standard Deviation of Diameter 0.5 mm 9.5.3.1 Height 147.5 mm to 152.5 mm 9.5.3 .2 End Flatness 0.5 mm 9.5.3.3 End Perpendicularity 1.0 mm 9.5.3.4 9.5.3.1 Using calipers, measure the diameter at the center and third points of the test specimen along axes that are 90 apart. Record each of the six measurements to the nearest 0.1 mm. Calculate the average and the standard deviation of the six measurements. The standard deviation shall be less than 0.5 mm. Reject specimens not meeting the average and standard deviation requirements listed in Table 1. The average diameter, reported to the nearest 0.1 mm, shall be used in all material property calculations. 9.5.3.2 Measure the height of the test specimen in accordance with Section 6.1.2 of ASTM D 3549. Reject specimens with an average height outside the height tolerance listed in Table 1. Record the average height. 9.5.3.3 Using a straightedge and feeler gauges, measure the flatness of each end. Place a straight edge across the diameter at three locations approximately 120 apart and measure the maximum departure of the specimen end from the straight edge using tapered end feeler gauges. For each end record the maximum departure along the three locations as the end flatness. Reject specimens with end flatness exceeding 0.5 mm.

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55 9.5.3.4 Using a combination square and feeler gauges, measure the perpendicularity of each end. At two locations approximately 90 apart, place the blade of the combination square in contact with the specimen along the axis of the cylinder, and the head in contact with the highest point on the end of the cylinder. Measure the distance between the head of the square and the lowest point on the end of the cylinder using tapered end feeler gauges. For each end, record the maximum measurement from the two locations as the end perpendicularity. Reject specimens with end perpendicularity exceeding 1.0 mm. 9.6 Test Specimen Density and Air Voids 9.6.1 Determine the maximum specific gravity of the mixture in accordance with AASHTO T 209 (If long-term conditioning has been used, determine the maximum specific gravity on the long-term conditioned loose mix sample). Record the maximum specific gravity of the mixture. 9.6.2 For dense- and gap-graded mixtures, determine the bulk specific gravity of the test specimen in accordance with AASHTO T 166. Record the bulk specific gravity of the test specimen. Note 10 When wet coring and sawing methods are used, measure the immersed mass followed by the surface dry mass followed by the dry mass to minimize drying time and expedite the specimen fabrication process. 9.6.3 For open-graded mixtures, determine the bulk specific gravity of the test specimen in accordance with Section 6.2 of AASHTO T 269. Record the bulk specific gravity of the test specimen. 9.6.4 Compute the air void content of the test specimen in accordance with AASHTO T 269. Record the air void content of the test specimen. Reject test specimens exceeding the air void tolerances specified in the appropriate Standard Method of Test. 9.7 Test Specimen Storage 9.7.1 Mark the test specimen with a unique identification number. 9.7.2 Store the test specimen on end on a flat shelf in a room with temperature controlled between 15 and 27 C until tested. Note 11 Definitive research concerning the effects of test specimen aging on various mechanical property tests has not been completed. Some users wrap specimens in Saran wrap and minimize specimen storage time to two weeks.

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56 10. REPORTING 10.1 Unique test specimen identification number. 10.2 Mixture design number for link to pertinent mixture design data including design compaction level and air void content, asphalt binder type and grade, binder content, binder specific gravity, aggregate types and bulk specific gravitities, consensus aggregate properties, and maximum specific gravity. 10.3 Type of aging used. 10.4 Maximum specific gravity for the aged condition. 10.5 Gyratory specimen target height (Optional). 10.6 Gyratory specimen bulk specific gravity (Optional). 10.7 Gyratory specimen air void content (Optional). 10.8 Test specimen average height. 10.9 Test specimen average diameter. 10.10 Test specimen bulk specific gravity. 10.11 Test specimen air void content. 10.12 Test specimen end flatness for each end. 10.13 Test specimen end parallelism for each end. 10.14 Remarks concerning deviations from this standard practice. 11. KEYWORDS Performance test specimens; gyratory compaction

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57 APPENDIX A METHOD FOR ACHIEVING TARGET AIR VOID CONTENT (NONMANDATORY INFORMATION) A1. PURPOSE A1.1 This Appendix presents a procedure for estimating the mass of mixture required to produce test specimens at a target air void content. It was developed to reduce the number of trial specimens needed obtain a target air void content for a specific mixture. A1.2 This procedure can be used with either plant produced or laboratory prepared mixture. A2. SUMMARY A2.1 Trial test specimens are prepared as described in this standard practice from gyratory specimens produced with a standard mass of 6,650 g and compacted to a standard height of 170 mm. A2.2 Based on the air void content of the trial specimens, the mass of mixture required to produce test specimens at a target air void content is estimated using a regression equation. Background information regarding the regression equation is presented in Section A4. A2.3 To use this method, it is critical that all gyratory specimens are prepared to a standard height of 170 mm. The approach described in Section A4 can be used to develop a similar equation for other gyratory specimen heights. A3. PROCEDURE A3.1 Prepare trial test specimen 1 and trial test specimen 2 following this standard practice from gyratory specimens produced with a standard mass of 6,650 g and compacted to a standard height of 170 mm. A3.2 Determine the air void content of trial test specimen 1 and trial test specimen 2. A3.3 Calculate the average air void content of the two specimens and designate this as Vas. A3.4 Estimate the mass of mixture, Wt, required to produce test specimens with a target air void content of Vat using Equation A1.

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58 Va t Wt = 7175 - (525) (A1) Va s where: Wt = estimated mass of mixture required to produce a gyratory specimen for a test specimen with a target air void content of Vat, g Vat = target air void content for the test specimen, vol % Vas = test specimen air void content produced with a gyratory mass of 6,650 g, vol % A3.5 Prepare trial test specimen 3 following this standard practice from a gyratory specimen produced with the target mass estimated in Section A3.4 and compacted to the standard height of 170 mm. A3.6 Determine the air void content of trial test specimen 3. A3.7 If the air void content of trial test specimen 3 is within 0.5 percent of the target, use the mass determined in A3.4 as the target mass for test specimen production. A3.8 If the air void content of trial test specimen 3 is not within 0.5 percent of the target, prepare trial specimen 4 using 50g less than calculated in A3.4 and trial test specimen 5 using 50g more than calculated in A3.4. A3.9 Determine the air void content of trial test specimen 4 and trial test specimen 5. A3.10 Plot the air void content of trial test specimens 3, 4, and 5 (y) against the mass of mixture used to prepare the gyratory specimen (x), and draw the best-fit line through the three data points. A3.11 From the best-fit line, determine the mass of mixture needed to produce a test specimen with the target air void content. A3.12 Use the mass determined in A3.11 as the target mass for test specimen production. A4. BACKGROUND A4.1 The method described in this Appendix was developed by the Arizona State University during NCHRP Project 9-19. It is based on analysis of 38 different mixtures, where test specimens were prepared to varying target air void contents representative of in-situ conditions. A4.2 For a given mixture, when gyratory specimens are prepared to a specific height, the relationship between the mixture mass used to prepare the gyratory specimen and the air void content of the test specimens was found to be linear.

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59 Va = I + S (W ) (A2) where: Va = test specimen air void content, vol % W = mass of mixture used to produce the gyratory specimen I = intercept of the regression line S = slope of the regression line A4.3 When a wide range of mixtures is considered, the intercepts and slopes for individual mixtures were also found to be linearly related. I = -C ( S ) (A3) where: I = intercept of individual mixture regression lines S = slope of individual mixture regression lines C = constant A4.4 In the NCHRP Project 9-19 research, the constant, C, was found to be 7,175 for gyratory specimens prepared to a standard height of 170 mm. Substituting this constant into Equation A3, then substituting Equation A3 into Equation A2 and simplifying, yields an equation relating the air void content of the test specimen to the mass of mixture used to prepare the gyratory specimen to the standard height of 170 mm. Va = S (W - 7175) (A4) A4.5 If gyratory specimens are compacted using a standard mass, Ws, and the air void contents for the resulting test specimens are determined to be Vas, then Equation A4 can be solved for the slope. Va s S= (A5) W s - 7175 where: Vas = test specimen air void content produced with a gyratory mass of Ws, vol % Ws = mass of mixture used to produce the gyratory specimen, g S = slope of the regression line A4.6 Using the slope from Equation A5, the target gyratory specimen mass, Wt, required to produce a test specimen with a specific air void content, Vat, can be estimated by substituting Equation A5 into Equation A4 and simplifying. Va t Wt = 7175 + (W s - 7175) (A6) Va s

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60 where: Wt = estimated mass of mixture required to produce a gyratory specimen for a test specimen with a target air void content of Vat, g Vat = target air void content for the test specimen. Vas = test specimen air void content produced with a gyratory mass of Ws, vol % Ws = mass of mixture used to produce the gyratory specimen A4.7 For a standard mixture mass of 6,650 g, which was the average mass used in the NCHRP 9-19 study, Equation A6 reduces to. Va t Wt = 7175 - (525) (A6) Va s where: Wt = estimated mass of mixture required to produce a gyratory specimen for a test specimen with a target air void content of Vat, g Vat = target air void content for the test specimen. Vas = test specimen air void content produced with a gyratory mass of Ws, vol % Ws = mass of mixture used to produce the gyratory specimen

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61 APPENDIX B TEST SPECIMEN UNIFORMITY (NONMANDATORY INFORMATION) B1. PURPOSE B1.1 This Appendix presents a procedure for assessing the uniformity of the air void content in test specimens produced using this standard practice. B1.2 The approach tests the significance of the difference in mean bulk specific gravity between the top and bottom third of the specimen relative the middle third. B1.3 The procedure can be used to determine the height for preparing gyratory specimens with a specific compactor to minimize within sample variations in air voids. B2. SUMMARY B2.1 Three test specimens are prepared as described in this standard practice from gyratory specimens produced with the same mixture mass and compacted to the same height. B2.2 The test specimens are cut into three slices of equal thickness and the bulk specific gravity or each slice is determined. B2.3 A statistical hypothesis test is conducted to determine the significance of differences in the mean bulk specific gravity of the top and bottom slices relative to the middle. B3. PROCEDURE B3.1 Prepare three test specimens following this standard practice to a target air void content of 5.5 percent. All three specimens shall have air void contents within the range of 5.0 to 6.0 percent. B3.2 Label the top, middle, and bottom third of each specimen, then saw the specimens at the third points. B3.3 Determine the bulk specific gravity of each of the nine test section slices in accordance with AASHTO T 166 for dense- and gap-graded mixtures or AASHTO T 269 for open-graded mixtures. B3.4 Assemble a summary table of the bulk specific gravity data where each column contains data for a specific slice, and each row contains the data from a specific core.

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62 B3.5 For each column, compute the mean and variance of the bulk specific gravity measurements using Equations B1 and B2. 3 y i =1 i y= (B1) 3 3 (y i =1 i - y) 2 s2 = (B2) 2 where: y = slice mean s2 = slice variance yi = measured bulk specific gravities B3.6 Statistical Comparison of Means- Compare the mean bulk specific gravity of the top and bottom slices to the middle slice using the hypothesis tests described below. In the descriptions below, subscripts "t", "m", and "b" refer to the top, middle, and bottom slices, respectively. B3.6.1 Check the top relative to the middle. Null Hypothesis: The mean bulk specific gravity of the top slice equals the mean bulk specific gravity of the middle slice, t = m 2 2 Alternative Hypothesis: The mean bulk specific gravity of the top slice is not equal the mean bulk specific gravity of the middle slice, t m 2 2 Test Statistic: (yt - y m ) t= (B3) 0.8165( s ) where: st + s m 2 2 s= (B4) 2 y t = computed mean for the top slices

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63 y m = computed mean for the middle slices st2 = computed variance for the top slices sm2 = computed variance for the middle slices Region of Rejection: For the sample sizes specified, the absolute value of the test statistic must be less than 2.78 to conclude that bulk specific gravity of the top and middle slices are equal. B3.6.2 Check the bottom relative to the middle. Null Hypothesis: The mean bulk specific gravity of the bottom slice equals the mean bulk specific gravity of the middle slice, b = m 2 2 Alternative Hypothesis: The mean bulk specific gravity of the bottom slice is not equal the mean bulk specific gravity of the middle slice, b m 2 2 Test Statistic: (y b - y m ) t= (B5) 0.8165( s ) where: sb + s m 2 2 s= (B4) 2 y b = computed mean for the bottom slices y m = computed mean for the middle slices sb2 = computed variance for the bottom slices sm2 = computed variance for the middle slices Region of Rejection: For the sample sizes specified, the absolute value of the test statistic must be less than 2.78 to conclude that bulk specific gravity of the bottom and middle slices are equal. B4. ANALYSIS B4.1 Significant differences in the bulk specific gravity of the top and bottom slices relative to the middle indicate a systematic variation in density within the specimen.

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64 B4.2 Specimens with differences for the top and/or bottom slices relative to the middle slices on the order of 0.025 have performed satisfactorily in the dynamic modulus, flow number, flow time, and continuum damage fatigue tests. B4.3 Changing the height of the gyratory specimen can improve the uniformity of the density in the test specimen.