AASHTO R 68-2015 Standard Practice for Preparation of Asphalt Mixtures by Means of the Marshall Apparatus.pdf

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1、Standard Practice for Preparation of Asphalt Mixtures by Means of the Marshall Apparatus AASHTO Designation: R 68-151American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001TS-2d R 68-1 AASHTO Standard Practice for Preparation

2、 of Asphalt Mixtures by Means of the Marshall Apparatus AASHTO Designation: R 68-1511. SCOPE 1.1. This standard practice describes procedures for the compaction of cylindrical specimens of asphalt mixtures using the Marshall compaction hammer. This practice is for use with mixtures containing asphal

3、t binder or asphalt cutback and aggregate up to 25.4-mm (1-in.) maximum size. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M 231, Weighing Devices Used in the Testing of Materials R 30, Mixture Conditioning of Hot Mix Asphalt (HMA) T 166, Bulk Specific Gravity (Gmb) of Compacted Hot Mix Asphalt (H

4、MA) Using Saturated Surface-Dry Specimens T 168, Sampling Bituminous Paving Mixtures T 275, Bulk Specific Gravity (Gmb) of Compacted Hot Mix Asphalt (HMA) Using Paraffin-Coated Specimens T 331, Bulk Specific Gravity (Gmb) and Density of Compacted Hot Mix Asphalt (HMA) Using Automatic Vacuum Sealing

5、Method 3. APPARATUS 3.1. Specimen Mold AssemblyMold cylinders 101.6 mm (4 in.) in diameter by 76.2 mm (3 in.) in height, base plates, and extension collars shall conform to the details shown in Figure 1. Three mold cylinders are recommended. 2015 by the American Association of State Highway and Tran

6、sportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d R 68-2 AASHTO Figure 1Specimen Mold Assembly Table 1Table of Equivalents for Figures 1 and 3 Metric Equiva- lents, mm U.S. Customary Units, in. Metric Equiva- lents, mm U.S. Customary Units, in. Metric Equiv

7、a- lents, mm U.S. Customary Units, in. Metric Equiva- lents, mm U.S. Customary Units, in. 0.11 0.005 17.5 11/1658.7 25/16104.8 41/80.8 1/3219.0 3/463.5 21/2108.7 49/321.6 1/1622.2 7/869.8 23/4109.1 419/643.2 1/823.8 15/1673.0 27/8114.3 41/24.8 3/1625.4 1 76.2 3 117.5 45/86.4 1/428.6 11/882.6 31/4120

8、.6 43/47.1 9/3231.8 11/487.3 37/16128.6 51/169.5 3/834.9 13/898.4 37/8130.2 51/812.6 0.496 38.1 11/2101.2 363/64146.0 53/412.67 0.499 41.3 15/8101.35 3.990 152.4 6 12.7 1/244.4 13/4101.47 3.995 158.8 61/414.3 9/1650.8 2 101.6 4 193.7 75/815.9 5/857.2 21/4101.73 4.005 685.8 27 3.2. Specimen Extractor

9、Steel, in the form of a disk with a diameter not less than 100 mm (3.95 in.) and 12.7 mm (1/2in.) thick for extracting the compacted specimen from the specimen mold with CollarCompactionMoldBase PlateCompaction Mold Assembledwith Collar and Base PlateSteel-Cadmium PlatedCompaction MoldSymmetricalabo

10、ut this CL363/64in. D33/4in. D4.005 in.3.995 in.41/2-in. O.D.419/64in.49/32-in. Dia.41/2-in. O.D.41/8-in. I.D.3/8in.9/16in.1/4in.9/32in.23/4in.1/4in.37/16in.1/8in. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applic

11、able law.TS-2d R 68-3 AASHTO the use of the mold collar. A suitable bar is required to transfer the load from the ring dynamometer adapter to the extension collar while extracting the specimen. A hydraulic jack or similar device may also be used provided specimens are not damaged during extraction.

12、3.3. Compaction Hammer: 3.3.1. Manual HammerThe compaction hammer (Figure 2) shall have a flat, 98.4 3.2 mm (37/8 1/8in.) circular tamping face and a 4536 9 g (10 0.02 lb) sliding weight (including a safety finger guard if so equipped) with a free fall of 457.2 1.524 mm (18 0.06 in.). 3.3.2. Automat

13、ic HammerAn automatic hammer shall meet the requirements listed for manual hammers in Section 3.3.1. The automatic hammer consists of the mechanical compactor, an automatic counter, a tapered-foot hammer assembly for rotating-mold models or a flat-foot hammer assembly for stationary mold models. To

14、calibrate the automatic hammer to the manual hammer, compact six specimens: three specimens using the manual hammer and three specimens using the automatic hammer. Use the same number of blows for each specimen. After the specimens have cooled to room temperature, use T 166, T 275, or T 331 to deter

15、mine the average bulk densities of the two sets of specimens. If the bulk densities of the two sets of specimens are within 2.0 percent of each other, then the results are comparable. If the results are not within 2.0 percent of each other, then the tests need to be repeated using more or fewer blow

16、s on the automatic hammer to achieve a comparable density. Figure 2Compaction Hammer (Manual) 3.4. Compaction PedestalThe compaction pedestal shall consist of a 203.2-by-203.2-by-457.2-mm (8-by-8-by-18-in.) wooden post capped with a steel plate with minimum dimensions of 304.8-by-304.8-by-25.4-mm (1

17、2-by-12-by-1-in.). The wooden post shall have an average dry weight of 0.67 to 0.77 g/cm3(42 to 48 lb/ft3). The wooden post shall be secured by four angle brackets to a solid concrete slab. The steel cap shall be firmly fastened to the post. The pedestal assembly shall be installed so that the post

18、is plumb and the cap is level. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d R 68-4 AASHTO 3.5. Specimen Mold HolderMounted on the compaction pedestal so as to center the compaction mold over the

19、 center of the post. It shall hold the compaction mold, collar, and base plate securely in position during compaction of the specimen. 3.6. Ovens or Hot PlatesOvens or hot plates shall be provided for heating aggregates, asphalt material, specimen molds, compaction hammers, and other equipment to th

20、e required mixing and molding temperatures. It is recommended that the heating units be thermostatically controlled so as to maintain the required temperature within 2.8C (5F). Suitable shields, baffle plates, or sand baths shall be used on the surfaces of the hot plates to minimize localized overhe

21、ating. 3.7. Heating DeviceA small hot plate with continuously variable heating rate, a sand bath, infrared lamp, or other suitable device shall be available for supplying sufficient heat under the mixing bowl to maintain the aggregate and asphalt material at the desired temperature during mixing. If

22、 a hot plate is used, a wire mesh or similar material shall be placed on the hot plate to prevent direct contact between the hot plate and mixing bowl. 3.8. Mixing ApparatusMechanical mixing is recommended. Any type of mechanical mixer may be used provided it can be maintained at the required mixing

23、 temperature and will produce a well- coated, homogeneous mixture of the required amount in the allowable time, and further provided that essentially all of the batch can be recovered. A metal pan or bowl of sufficient capacity and hand mixing may also be used. 3.9. Air BathThe air bath for asphalt

24、cutback mixtures shall be thermostatically controlled and shall maintain the air temperature at 25 1C (77 2F). 3.10. ThermometersFor determining temperatures of aggregates, asphalt binder, and asphalt mixtures. Armored-glass, dial type, or digital thermometers with metal stems are recommended. A ran

25、ge from 9.9 to 204C (50 to 400F) with sensitivity of 2.8C (5F) is required. 3.11. Balance A balance meeting the requirements of M 231, Class G 2, for determining the mass of aggregates, binder and asphalt mixture. 3.12. Miscellaneous EquipmentFlat-bottom metal pans or other suitable containers for h

26、eating aggregates, containers (gill-type, beakers, pouring pots, or saucepan) for heating asphalt, flat bottom scoop for batching aggregates, steel trowel (garden type) or spatula for spading and hand mixing, gloves for handling hot equipment, paper disks, marking crayons for identifying specimens,

27、and a large spoon for placing mixture in specimen molds. 4. PROCEDURE 4.1. Number of SpecimensPrepare at least three specimens for each combination of aggregates and bitumen content. 4.2. Preparation of AggregatesDry aggregates to constant mass at 105 to 110C (221 to 230F) and separate the aggregate

28、s by dry-sieving into the desired size fractions. The following size fractions are recommended: 25.0 to 19.0 mm (1 to 3/4in.) 19.0 to 9.5 mm (3/4to 3/8in.) 9.5 mm to 4.75 mm (3/8in. to No. 4) 4.75 mm to 2.36 mm (No. 4 to No. 8) Passing 2.36 mm (No. 8) 2015 by the American Association of State Highwa

29、y and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d R 68-5 AASHTO 4.3. Determination of Mixing and Compacting Temperatures: 4.3.1. The temperatures to which the asphalt binder and asphalt cutback must be heated to produce a viscosity of 170 20 cSt s

30、hall be the mixing temperature. 4.3.2. The temperature to which asphalt binder must be heated to produce a viscosity of 280 30 cSt shall be the compacting temperature. 4.3.3. From a composition chart for the asphalt cutback used, determine from its viscosity at 60C (140F) the percentage of solvent b

31、y mass. Also determine from the chart the viscosity at 60C (140F) of the asphalt cutback after it has lost 50 percent of its solvent. The temperature determined from the viscosity temperature chart to which the asphalt cutback must be heated to produce a viscosity of 280 30 cSt after a loss of 50 pe

32、rcent of the original solvent content shall be the compaction temperature. 4.4. Preparation of Mixtures (Laboratory Prepared): 4.4.1. An initial batch shall be mixed for the purpose of “buttering” the mixture bowl and stirrers. This batch shall be emptied after mixing and the sides of the bowl and s

33、tirrers shall be cleaned of mixture residue by scraping with a small limber spatula but shall not be wiped with cloth or washed clean with solvent, except when a change is to be made in the binder or at the end of a run. 4.4.2. Weigh into separate pans for each test specimen the amount of each size

34、fraction required to produce a batch that will result in a compacted specimen 63.5 1.27 mm (2.5 0.05 in.) in height (about 1200 g). 4.4.3. Mix the aggregate in each pan and place the pans on a hot plate or in the oven and heat to a temperature not exceeding the mixing temperature established in Sect

35、ion 4.3 by more than approximately 28C (50F) for asphalt mixtures and 14C (25F) for cutback asphalt mixes. 4.4.4. Heat, to the established mixing temperature, just sufficient asphalt material for the batch in a separate container. 4.4.5. Charge the mixing bowl with the heated aggregate. Form a crate

36、r in the dry-blended aggregate and weigh the preheated required amount of asphalt material into the mixture. For mixes prepared with cutback asphalt, introduce the mixing blade in the mixing bowl and determine the total mass of the mix components plus bowl and blade before proceeding with mixing. Ca

37、re must be exercised to prevent loss of the mix during mixing and subsequent handling. At this point, the temperature of the aggregate and asphalt material shall be within the limits of the mixing temperature established in Section 4.3. 4.4.6. Mix the aggregate and asphalt material rapidly until tho

38、roughly coated. To maintain proper mixing temperature, one of the methods described in Section 3.8 may be used. 4.4.7. Cure mixtures containing asphalt binder in accordance with R 30. 4.4.8. Cure asphalt cutback mixtures in a ventilated oven maintained at approximately 11.1C (20F) above the compacti

39、on temperature. Curing is to be continued in the mixing bowl until the precalculated weight of 50 percent solvent loss or more has been obtained. The mix may be stirred in a mixing bowl during curing to accelerate the solvent loss. However, care should be exercised to prevent loss of the mix. Weigh

40、the mix during curing in successive intervals of 15 min initially and less than 10-min intervals as the weight of the mix at 50 percent solvent loss is approached. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applic

41、able law.TS-2d R 68-6 AASHTO 4.5. Preparation of Mixture (Plant Produced): 4.5.1. Obtain the sample in accordance with T 168. 4.5.2. Reduce the sample in accordance with R 47 to a sample size that will result in compacted specimens 63.5 1.27 mm (2.5 0.05 in.) in height as described in Section 4.4.2.

42、 4.5.3. Place the sample into a pan to a uniform thickness. 4.5.4. Bring the asphalt mixture to the compaction temperature range by careful, uniform heating in an oven immediately prior to compaction. 4.6. Compaction of Specimens: 4.6.1. Thoroughly clean the specimen mold assembly and the face of th

43、e compaction hammer and heat them either in boiling water, on the hot plate, or in an oven, to a temperature between 93.3 and 148.9C (200 and 300F). 4.6.2. Place a piece of filter paper or paper towel, cut to size, in the bottom of the mold before the mixture is introduced. 4.6.3. Place the entire b

44、atch in the mold, and spade the mixture vigorously with a heated spatula or trowel 15 times around the perimeter and 10 times over the interior. Smooth the surface of the mix with a trowel to a slightly rounded shape. Remove the collar if necessary. Temperatures of the mixtures immediately prior to

45、compaction shall be within the limits of the compaction temperature established in Section 4.3. If the temperature of the specimen is too high, allow the specimen to cool within the range of compaction temperatures; however, if the mixture is below compaction temperature, remove the mixture from the

46、 mold and replace it in the oven until the desired temperature is reached. Next, repeat the steps in this section. This process should not be repeated more than once. The material should be heated for the minimum time required to achieve the compaction temperature. Note 1Excessive heating times may

47、cause oxidation and loss of volatiles and should be avoided. 4.6.4. Replace the collar, then place a piece of filter paper or paper toweling cut to size on top of the mixture and place the mold assembly on the compaction pedestal in the mold holder, and unless otherwise specified, apply 50 or 75 blo

48、ws with the compaction hammer with a free fall in 457.2 mm (18 in.). Hold the axis of the compaction hammer perpendicular to the base of the mold assembly during compaction. Remove the base plate and collar, and reverse and reassemble the mold. Apply the same number of compaction blows to the face o

49、f the reversed specimen. 4.6.5. After compaction, remove the base plate, carefully extract the specimen from the mold and transfer to a smooth, flat surface. 4.6.6. Allow the specimen to stand overnight at room temperature. Note 2In general, specimens shall be cooled as specified in Section 4.6.6. When more rapid cooling is desired, table fans may be used. Mixtures that lack sufficient cohesion to result in the required cylindrical shape on removal from the mold im