J.4_38-mm_Specimen_Fabrication.pdf

DRAFT PROCEDURE

Preparation of Small Cylindrical Performance Test Specimens Using the Superpave

Gyratory Compactor (SGC) and Field Cores

1. SCOPE

1.1. This practice covers the use of a Superpave gyratory compactor (SGC) or field cores to prepare 38-mm-diameter by 110-mm-height performance test specimens for use in a variety of axial compression and tension performance tests. This practice is intended for dense-graded asphalt mixtures with nominal maximum aggregate sizes up to 25.0 mm.

1.2. This standard may involve hazardous material, operations, and equipment. This standard does not purport to address all 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 use.

2. REFERENCED DOCUMENTS

2.1. AASHTO Standards:

R 30, Mixture Conditioning of Hot Mix Asphalt

T 166, Bulk Specific Gravity (Gmb) of Compacted Hot Mix Asphalt (HMA) Using Saturated

Surface Dry Specimens

T 209, Theoretical Maximum Specific Gravity (Gmm) and Density of Hot Mix Asphalt (HMA)

T 269, Percent Air Voids in Compacted Dense and Open Asphalt Mixtures

T 312, Preparing and Determining the Density of Asphalt Mixture Specimens by Means of the

Superpave Gyratory Compactor

T 342, Determining the Dynamic Modulus of Hot Mix Asphalt (HMA)

Determining the Dynamic Modulus for Asphalt Mixtures Using Small Specimens in the

Asphalt Mixture Performance Tester (AMPT)

Determining the Damage Characteristic Curve and Analysis Parameters Using Small

Specimens in the Asphalt Mixture Performance Tester (AMPT) Cyclic Fatigue Test

2.2. ASTM Standard:

D3549/D3549M, Standard Test Method for Thickness or Height of Compacted Bituminous

Paving Mixture Specimens

3. TERMINOLOGY

3.1. SGC specimen—a 150-mm-diameter by 180-mm-tall (minimum) cylindrical specimen prepared in an SGC meeting the requirements of T 312.

3.2. 38-mm test specimen—a 38-mm-diameter by 110-mm-tall cylindrical specimen that is cored and sawed from an SGC 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 configuration is measured using a precision square with the beam touching the cylinder parallel to its axis (or prisms) and the blade touching the highest point on the end of the cylinder (or prism). The distance between the blade of the square and the lowest pint on the end of the cylinder is checked with 1.0-mm-diameter wire or feeler gauges.

3.4. end planeness—maximum departure of the specimen end from a plane. This dimension is checked using a straightedge and 0.5-mm-diameter wire or feeler gauges.

4. SUMMARY OF PRACTICE

4.1. This practice presents methods for extracting 38-mm-diameter by 110-mm-tall cylindrical test specimens from SGC specimens and field cores 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 small-specimen (|E*|) and (fatigue).

5.2. This practice may also be used to prepare specimens for other tests requiring 38-mm-diameter by 110-mm-height cylindrical test specimens.

6. APPARATUS

6.1. Superpave Gyratory Compactor—Meeting the requirements of T 312 and capable of preparing 150-mm-diameter specimens that are a height of at least 180 mm.

6.2. Mixture Preparation Equipment—Balances, ovens, thermometers, mixer, pans, and other miscellaneous equipment needed to prepare SGC specimens in accordance with T 312, perform bulk specific gravity (Gmb) measurements in accordance with T 166, and perform maximum specific gravity

(Gmm) measurements in accordance with T 209.

6.3. Core Drill—An air- or water-cooled, diamond-bit core drill capable of cutting cores to a nominal diameter of 38-mm and meeting the dimensional requirements of Section 9.5.4. The core drill shall be equipped with a fixture for holding the SGC specimens or field cores from which the test specimens are being extracted.

Note 1—Core drills with fixed and adjustable rotational speed have been used successfully to prepare specimens meeting the dimensional tolerances given in Section 9.5.4. Rotational speeds from 450 to 750 rpm have been used.

Note 2—Core drills with automatic and manual feed rate have been used successfully to prepare specimens meeting the dimensional tolerances given in Section 9.5.4.

6.4. Masonry Saw—An air- or water-cooled, diamond-bladed masonry saw capable of cutting specimens to a nominal length of 110 mm and meeting the tolerances for end perpendicularity and end flatness given in Section 9.5.4.

Note 3—Heavy duty tile saws with good stability have been found effective for sawing 38-mm-diameter specimens. Larger masonry saws may not produce specimens meeting the dimensional tolerances. Saws require a fixture to securely hold the specimen during sawing and to control the feed rate.

6.5. Square—Precision square with 8-in. beam and 12-in. blade. McMaster Carr Pro-Value Square, Catalog

Number 2278A21 or equivalent.

6.6. 1.0-mm Diameter Carbon Steel Wire—0.039-in. (1-mm) diameter carbon steel wire, McMaster Carr

Catalog Number 8907K42 or equivalent.

6.7. 0.5-mm Diameter Carbon Steel Wire—0.020-in. (0.5-mm) diameter carbon steel wire, McMaster Carr

Catalog Number 8907K21 or equivalent.

6.8. Feeler Gauges—Tapered-leaf feeler gauges in 0.05-mm increments.

6.9. Metal Ruler—Capable of measuring 150-mm-long (nominal) specimens to the nearest 1 mm.

6.10. Calipers—Capable of measuring 100-mm-diameter (nominal) specimens to the nearest 0.1 mm.

7. HAZARDS

7.1. This practice and associated standards involve handling of hot asphalt binder, aggregates, and HMA. It also includes 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 or verification are included in the AASHTO standards referenced in Section 2. Refer to the pertinent section of the referenced standards for information concerning calibration or verification.

9. PROCEDURE A – FABRICATION FROM GYRATORY SPECIMENS

9.1. Asphalt Mixture Preparation:

9.1.1. Prepare asphalt mixture for each SGC specimen in accordance with T 312 and prepare a companion test specimen for maximum specific gravity (Gmm) in accordance with T 209.

9.1.2. The mass of asphalt mixture needed for each specimen will depend on the SGC specimen height, the Gmm of the mixture, the nominal maximum aggregate size, gradation (coarse or fine), and target air void content of the test specimens.

Note 4—Appendix X1 describes one procedure for determining the mass of asphalt mixture required to reach a specified test specimen target air void content.

9.1.3. Perform conditioning on the asphalt mixture for the test specimens and companion Gmm sample in accordance with R 30.

9.2. SGC Specimen Compaction:

9.2.1. Compact the SGC specimens to a height of 180 mm or higher, in accordance with T 312, carefully following the exceptions noted.

9.2.2. Pour the mixture into the center of the mold to minimize air void variation between samples. Pouring material down the sides of the mold will result in lower air voids on that side of the mold.

9.2.3. Charge the mold in two equal lifts, and rod the sample 20 times after each lift, to minimize vertical air void variance.

9.3. Long-Term Conditioning (optional):

9.3.1. If it is desired to simulate long-term aging, condition the SGC specimen in accordance with R 30.

9.3.2. To obtain accurate volumetric measurements on the long-term-conditioned specimens, also condition a sample of short-term-conditioned loose asphalt mixture meeting the sample size requirements of T

209 in accordance with R 30.

9.4. SGC Specimen Density and Air Voids (Optional):

9.4.1. Determine the Gmm of the asphalt mixture in accordance with T 209. If long-term conditioning has been used, determine the Gmm on the long-term-conditioned loose asphalt mixture. Record the Gmm of the mixture.

9.4.2. Determine Gmb of the SGC specimen in accordance with T 166. Record the Gmb of the SGC specimen.

9.4.3. Compute the air void content of the SGC specimen in accordance with T 269. Record the air void content of the SGC specimen.

Note 5—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 SGC specimen. However, monitoring SGC specimen density can identify improperly prepared specimens early in the specimen fabrication process. Information on SGC specimen air voids and test specimen air voids will also assist the laboratory in establishing potentially more precise methods than Appendix X1 for preparing test specimens to a target air void content

9.5. Test Specimen Preparation:

9.5.1. Prepare the gyratory specimen by marking the location(s) where the cores will be taken. All cores must be taken within the inner 100 mm of the gyratory specimen. As many as four 38-mm diameter cores can be extracted from one gyratory specimen, as shown by the gray circles in Figure 1. The optimal lines to mark to extract four gyratory specimens are shown in white in Figure 1.

Figure 1-Graphic of a marked gyratory specimen

9.5.2. Drill a core of nominal diameter of 38 mm from the SGC specimen. Both the SGC 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 Table 1.

9.5.3. Saw the ends of the core to obtain a test specimen of a nominal height of 110 mm. Both the core and the saw shall be adequately supported to ensure that the resulting test specimen meets the tolerances given in Table 1 for height, end flatness, and end perpendicularity.

Note 6—With most equipment, it is better to perform the coring before the sawing. However, these operations may be performed in either order as long as the dimensional tolerances in Table 1 are satisfied.

9.5.4. Test specimens shall meet the dimensional tolerances given in Table 1.

Table 1— Test Specimen Dimensional Tolerances

Item Specification Method Reference

Average diameter 36 to 40 mm 9.5.4.1

Standard deviation of diameter ≤0.5 mm 9.5.4.1

Height 107.5 to 112.5 mm 9.5.4.2

End flatness ≤0.5 mm 9.5.4.3

End perpendicularity ≤1.0 mm 9.5.4.4

9.5.4.1. Using calipers, measure the diameter at the center and third points of the test specimen along axes that are

90 degrees apart. Record each of the six measurements to the nearest 0.1 mm. Calculate the average and the standard deviation of the six measurements. Reject specimens not meeting the average and the standard deviation requirements given in Table 1. The average diameter, reported to the nearest 0.1 mm, shall be used in all material property calculations.

9.5.4.2. Measure the height of the test specimen in accordance with ASTM D3549/D3549M. Reject specimens with an average height outside the height tolerance listed in Table 1. Record the average height.

9.5.4.3. Using the blade of the precision square as a straightedge, check the flatness of each end at three locations approximately 120 degrees apart. At each location, place the blade of the precision square across the diameter of the specimens and check the maximum departure of the specimen from the blade using the 0.5-mm-diameter carbon steel wire or feeler gauge. Reject specimens if the 0.5-mm-diameter carbon steel wire fits between the blade and the specimen at any location.

9.5.4.4. Check the perpendicularity of each end of the specimen using the precision square and the 1.0 mm carbon steel wire at two locations approximately 90 degrees apart. Place the precision square on a table with the beam in contact with the table and the blade extending vertically. Place the long axis of the specimen on the beam such that the blade is in contact with the end of the specimen. Check the maximum departure of the specimen from the blade using the 1.0-mm-diameter carbon steel wire or feeler gauge. Reject any specimens if the 1.0-mm-diameter carbon steel wire fits between the blade and the specimen at any location.

9.6. Test Specimen Density and Air Voids:

9.6.1. Determine the Gmm of the asphalt mixture in accordance with T 209. If long-term conditioning has been used, determine the Gmm on the long-term-conditioned loose asphalt mixture. Record the Gmm of the mixture.

9.6.2. Determine Gmb of the test specimen in accordance with T 166. Record the Gmb of the SGC specimen.

Note 7—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. Compute the air void content of the SGC specimen in accordance with T 269. Record the air void content of the SGC specimen.

9.7. Test Specimen Storage:

9.7.1. Mark the test specimen with a unique identification number.

9.7.2. Store the test specimen, until tested, on its end on a flat shelf in a room with the temperature controlled between 15 and 27ºC.

Note 8—Definitive research concerning the effects of test specimen aging on various mechanical property tests has not been completed. Some users enclose specimens in plastic wrap, or minimize specimen storage time to two weeks, or both.

10. PROCEDURE B – FABRICATION FROM FIELD CORES

10.1. Field Core Preparation:

10.1.1. Obtain sufficient field cores for all testing and additional cores to provide sufficient material to conduct the maximum specific gravity (Gmm) test in accordance with T 209.

10.1.2. Mark the direction of traffic on the field core before coring in the field, if possible. Otherwise evaluate the field core and select the most probable direction of traffic.

10.1.3. Reduce the size of the field core, if needed, using the saw to make the field core a geometry which can be held stable by the fixture for coring and is suitable for extracting one or more specimens perpendicular to the direction of traffic. Before cutting, mark the direction of traffic on all sections of the field core.

10.2. Test Specimen Preparation:

10.2.1. Prepare the field core by marking where the cores will be taken. Two 38-mm diameter cores can be extracted from one 6-inch diameter field core, as shown by the gray rectangles in Figure 2.

Additional samples may be extracted from larger field cores, provided the samples are all extracted perpendicular to the direction of traffic.

Figure 1-Graphic of samples extracted from a 6-inch field core

10.2.2. Drill a core of nominal diameter of 38 mm from the SGC specimen. Both the field core 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 Table 1.

10.2.3. Saw the ends of the core to obtain a test specimen of a nominal height of 110 mm. Both the core and the saw shall be adequately supported to ensure that the resulting test specimen meets the tolerances given in Table 1 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 performed in either order as long as the dimensional tolerances in Table 2 are satisfied.

10.2.4. Test specimens shall meet the dimensional tolerances given in Table 1.

10.3. Test Specimen Density and Air Voids:

10.3.1. Procure sufficient material from separate field cores to determine the Gmm of the asphalt mixture in accordance with T 209.

10.3.2. Determine Gmb of the SGC specimen in accordance with T 166. Record the Gmb of the SGC 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.

10.3.3. Compute the air void content of the SGC specimen in accordance with T 269. Record the air void content of the SGC specimen

10.4. Test Specimen Storage:

10.4.1. Mark the test specimen with a unique identification number.

10.4.2. Store the test specimen, until tested, on its end on a flat shelf in a room with the temperature controlled between 15 and 27ºC.

Note 11—Definitive research concerning the effects of test specimen aging on various mechanical property tests has not been completed. Some users enclose specimens in plastic wrap, or minimize specimen storage time to two weeks, or both.

11. REPORTING

11.1. Report the following information:

11.1.1. Unique test specimen identification number;

11.1.2. Mixture design data including design compaction level and air void content, asphalt binder type and grade, binder content, binder specific gravities, aggregate types and specific gravities, aggregate consensus properties, and Gmm;

11.1.3. Type of conditioning used;

11.1.4. Gmm for the conditioned specimens;

11.1.5. SGC specimen target height (optional);

11.1.6. SGC specimen Gmb (optional);

11.1.7. SGC specimen air void content (optional);

11.1.8. Test specimen average height;

11.1.9. Test specimen average diameter;

11.1.10. Test specimen Gmb;

11.1.11. Test specimen air void content;

11.1.12. Test specimen end flatness for each end;

11.1.13. Test specimen end perpendicularity for each end; and

11.1.14. Remarks concerning deviations from this standard practice.

12. KEYWORDS

12.1. Gyratory compaction; performance test specimens

APPENDIXES (NONMANDATORY INFORMATION)

METHOD FOR ACHIEVING A TARGET AIR VOID CONTENT

X1.1. Purpose:

X1.1.1. This appendix presents a procedure for estimating the mass of asphalt mixture required to produce test specimens at a target air void content. It was developed to avoid compacting repeat trial specimens. A trial and error method which may use less material is available in PP 60 Appendix

X1.

X1.1.2. This procedure can be used with either plant-produced or laboratory-prepared asphalt mixtures.

X1.2. Summary:

X1.2.1. An estimate of the mass of mixture required is made knowing the maximum specific gravity of the mixture, Gmm, and the volume of the gyratory specimen.

X1.2.2. Three trial specimens are compacted to the target height, one at the target mass and the other two at the target mass ±100 grams. 100-mm diameter by 150-mm height specimens are extracted from each of the gyratory specimens.

X1.2.3. The air void contents of the trial specimens are measured and used to develop a relationship between gyratory specimen mass and test specimen air voids.

X1.3. Procedure:

X1.3.1. Measure the maximum specific gravity, Gmm, of the mixture in accordance with T 209.

X1.3.2. Calculate the mass of the mixture required for a gyratory specimen of target height, H, using Equation

X1.1:

Mass = [ 100−(𝑉𝑎𝑡+𝐹)

] ∗ 𝐺𝑚𝑚 ∗ 176.7147 ∗ 𝐻

(X1.1) where:

Mass = estimated mass of mixture to prepare a test specimen to the target air voids, g

Vat = target air void content for the test specimen, percent by volume

Gmm = maximum specific gravity for the mixture

H = height of the gyratory specimen, cm

F = air void adjustment factor: 1.0 for fine-graded; 1.5 for coarse-graded

X1.3.3. Using the estimated mass from Equation X1.1, prepare three trial gyratory specimens at the target mass and

±100 grams. Extract 100-mm diameter by 150-mm height specimens from each of the gyratory specimens.

X1.3.4. Measure the bulk specific gravity of the trial test specimens and calculate the air void content of the trial test specimens in accordance with Section 9.6.

X1.3.5. Prepare a plot of the gyratory specimen mass against the test specimen air void content. Fit a line to the three points as shown in Figure X1.1.

Figure X1.1-Example of Air Void Relationship Plot with Fitted Line and Equation

X1.3.6. Use the fitted line to determine the mass needed for the specific target air voids.

X1.3.7. This procedure does require three specimens, but it avoids the repeat compaction which may be needed in a trial-and-error procedure.

y = -80.0x + 7,479.7

7,060

7,080

7,100

7,120

7,140

7,160

7,180

7,200

7,220

7,240

3 3.5 4 4.5 5 5.5

G y ra to ry S p e c im e n

M a s s g

Test Specimen Air Voids (%)