1、Standard Method of Test for Bulk Specific Gravity (Gmb) and Density of Compacted Hot Mix Asphalt (HMA) Using Automatic Vacuum Sealing Method AASHTO Designation: T 331-131ASTM Designation: D6752/D6752M-11 American Association of State Highway and Transportation Officials 444 North Capitol Street N.W.
2、, Suite 249 Washington, D.C. 20001 TS-2c T 331-1 AASHTO Standard Method of Test for Bulk Specific Gravity (Gmb) and Density of Compacted Hot Mix Asphalt (HMA) Using Automatic Vacuum Sealing Method AASHTO Designation: T 331-131ASTM Designation: D6752/D6752M-11 1. SCOPE 1.1. This method covers the det
3、ermination of bulk specific gravity (Gmb) of specimens of compacted hot mix asphalt (HMA) mixtures. 1.2. This method should be used with samples that contain open or interconnecting voids and/or absorb more than 2.0 percent of water by volume, as determined by T 166. An agency may specify this metho
4、d as an alternative to T 275. 1.3. The bulk specific gravity (Gmb) of the compacted HMA may be used in calculating the unit mass of the mixture. 1.4. The values stated in SI units are to be regarded as the standard. 1.5. This standard may involve hazardous materials, operations, and equipment. This
5、standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS
6、 2.1. AASHTO Standards: M 231, Weighing Devices Used in the Testing of Materials T 166, Bulk Specific Gravity (Gmb) of Compacted Hot Mix Asphalt (HMA) Using Saturated Surface-Dry Specimens T 245, Resistance to Plastic Flow of Asphalt Mixtures Using Marshall Apparatus T 275, Bulk Specific Gravity (Gm
7、b) of Compacted Hot Mix Asphalt (HMA) Using Paraffin-Coated Specimens T 312, Preparing and Determining the Density of Asphalt Mixture Specimens by Means of the Superpave Gyratory Compactor 2.2. ASTM Standards: D6752/D6752M, Standard Test Method for Bulk Specific Gravity and Density of Compacted Bitu
8、minous Mixtures Using Automatic Vacuum Sealing Method D7227/D7227M, Standard Practice for Rapid Drying of Compacted Asphalt Specimens Using Vacuum Drying Apparatus E1, Standard Specification for ASTM Liquid-in-Glass Thermometers 2015 by the American Association of State Highway and Transportation Of
9、ficials.All rights reserved. Duplication is a violation of applicable law.TS-2c T 331-2 AASHTO 2.3. Other Document: FHWA-IF-02-044, NCAT Report No. 02-11, Bulk Specific Gravity Round-Robin Using the CoreLokTMVacuum Sealing Device 3. TERMINOLOGY 3.1. Definitions: 3.1.1. bulk specific gravity (of soli
10、ds)the ratio of the mass in air of a unit volume of a permeable material (including both permeable and impermeable voids normal to the material) at a stated temperature to the mass in air of equal density of an equal volume of gas-free distilled water at a stated temperature. The form of the express
11、ion shall be: Bulk specific gravity at x/yC where: x = temperature of the material; and y = temperature of the water. 3.1.2. constant massshall be defined as the mass at which further drying does not alter the mass by more than 0.05 percent when the mass is determined at 2-h intervals. 4. TEST SPECI
12、MENS 4.1. Test specimens may be either laboratory-compacted HMA mixtures or sampled from HMA pavements. The mixtures may be surface or wearing course, binder or leveling course, or hot mix base. 4.2. Size of SpecimensSpecimens shall conform to the requirements of T 166. 4.3. Specimens shall be taken
13、 from pavements with a core drill, diamond or carborundum saw, or by other suitable means. 4.4. Care shall be taken to avoid distortion, bending, or cracking of specimens during and after the removal from the pavement or mold. Specimens shall be stored in a safe, cool place. 4.5. Specimens shall be
14、free from foreign materials such as seal coat, tack coat, foundation material, soil, paper, or foil. 4.6. If desired, specimens may be separated from other pavement layers by sawing or other suitable means. Care should be exercised to ensure sawing does not damage specimens. Jagged edges or sharp ag
15、gregates may puncture the plastic bag. Specimen ends or planar edges may require sawing if the bag does not conform to the specimen in a uniform manner. 5. APPARATUS 5.1. Bag CutterA knife, scissors, or other types of clipping devices may be used to quickly open bags. 5.2. OvenThe oven shall be capa
16、ble of maintaining the appropriate temperature for drying specimens to a constant mass. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2c T 331-3 AASHTO 5.3. Weighing DeviceThe weighing device shall
17、have sufficient capacity, be readable to 0.1 percent of the sample mass or better, and conform to the requirements of M 231. The weighing device shall be equipped with a suitable suspension apparatus and holder to determine the mass of the specimen while suspended from the center of the scale pan of
18、 the weighing device. 5.4. Plastic BagsThe two most commonly used sizes of bags are designated as small and large size bags. The small bags shall have a minimum opening of 235 mm (9.25 in.) and a maximum opening of 260 mm (10.25 in.) with a mass of less than 35 g. The large bags shall have a minimum
19、 opening of 375 mm (14.75 in.) and a maximum opening of 394 mm (15.5 in.) with a mass of 35 g or more. The bags shall be made of a plastic material that will not adhere to asphalt film and shall be puncture-resistant, capable of withstanding sample temperatures of up to 70C (158F), impermeable to wa
20、ter, and contain no air channels for evacuation of air from the bag. The bags shall have a minimum thickness of 0.100 mm (0.004 in.) and a maximum thickness of 0.152 mm (0.006 in.). The manufacturer shall provide the bag correction factor (apparent specific gravity) of the bags (usually located in t
21、he operators manual). See the manufacturers recommendations to ensure proper handling of bags. 5.5. Specimen Sliding PlatesLevel and smooth-sided planar filler plates shall be inserted into the chamber to keep the samples of various heights level with the seal bar while being sealed. The plates shal
22、l be removable and of the appropriate dimensions to easily fit into the vacuum chamber. A smooth-sided specimen supporting plate shall easily slide on top of the smooth-sided plates. The opposite side of the smooth-sided specimen supporting plate shall have a cushioning membrane to help prevent tear
23、s in the plastic bag. The plate shall be large enough to fully support the specimen but small enough to allow movement during the sealing process. 5.6. Suspension ApparatusThe wire suspending the container shall be of the smallest practical size to minimize any possible effects of a variable immerse
24、d length. The suspension apparatus shall be constructed to enable the container to be immersed to a depth sufficient to cover it and the test sample during weighing. 5.7. ThermometerASTM 17C (17F), having a range of 19 to 27C (66 to 80F), graduated and conforming to ASTM E1. An electronic temperatur
25、e measuring device, such as a resistance thermometer or thermocouple, may be used. 5.8. Vacuum ChamberThe pump shall be capable of evacuating the sealed and enclosed chamber to 5 mmHg in 60 s at sea level. The chamber shall be large enough to seal samples of 150-by-350-by-150 mm (6-by-14-by-6 in.).
26、A sealing bar of sufficient length to fully seal small and large size bags shall be located inside the chamber. The heat setting shall be set according to the manufacturers recommendations and the bag composition. The device shall automatically seal the plastic bag and exhaust air back into the cham
27、ber in a controlled manner to ensure proper conformance of the plastic bag to the specimen. The air exhaust and vacuum operation time should be calibrated to bring the chamber to atmospheric pressure in 80 to 120 s after completion of the vacuum operation. The vacuum system should be provided with a
28、 latch to control chamber door opening. 5.9. Vacuum Gauge (Standardized)The standardized vacuum gauge shall be capable of being placed inside the automatic vacuum sealing device to verify vacuum performance and seal integrity. The gauge shall have a minimum range of 10 to 0 mmHg (10 to 0 torr) and s
29、hall be readable to 1 mmHg (1 torr) increments, as a minimum. 5.10. Water BathFor immersing the specimen in water while suspended under the weighing device, equipped with an overflow outlet for maintaining a constant water level and thermostatically controlled so as to maintain the bath at 25 1C (77
30、 1.8F). A heater and circulator may be attached. The circulator shall not be in use while recording sample masses. It is important that the water bath be of sufficient size to ensure sufficient space for the sample and the plastic bag suspension. A water bath with suggested minimum dimensions (lengt
31、h by width by depth) of 610- 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2c T 331-4 AASHTO by-460-by-460 mm (24-by-18-by-18 in.) or a large cylindrical container has been found to work well for th
32、is test method. (See Note 1.) Note 1If a cushioned holder is used inside the water bath, it should not have sharp edges. Cushioned holders with sharp edges have been found to puncture the plastic bags. A clip may be attached to the container to hold the plastic bags underwater and to keep edges of t
33、he plastic bags from touching the edges of the water bath. Water baths at eye level may help prevent tears in bags and assist in ease of use. 6. PROCEDURE 6.1. Initial Mass of Specimen in AirDry the specimen to a constant mass at a temperature of 52 3C (125 5F), or vacuum-dry the specimen according
34、to ASTM D7227/D7227M. Samples saturated with water shall initially be dried overnight and then the mass determined at 2-h drying intervals. Recently compacted laboratory samples that have not been exposed to moisture do not require drying. Cool the specimen to room temperature at 25 5C (77 9F), and
35、record the initial dry mass as A. It is important that the sample contain less than 5 g of water before it is exposed to vacuum. At high vacuum, water will evaporate, potentially causing the bag around the sample to loosen due to trapped gas, thus resulting in a higher volume determination and a low
36、er bulk specific gravity result. Note 2Bulk specific gravity (Gmb) determined by this method may be lower, and air voids higher, than the results obtained by T 166. The differences may be more pronounced for coarse and absorptive mixtures. Users of this test method are cautioned to evaluate any alte
37、ration in asphalt content or aggregate gradation for mix designs with a positive performance history. If this procedure will be used for control or assurance testing, users are cautioned to follow this procedure during the laboratory mix design. Note 3Laboratory-compacted specimens of 3000 to 6000 g
38、 may be considered at room temperature equilibrium after 2 h of cooling under a fan. The cooling time may be reduced for smaller specimens or if verified to have no significant differences in properties from those cooled to room temperature equilibrium. Note 4Some steps may be performed in conjuncti
39、on with T 166. 6.2. Sealing the SpecimenSelect an appropriately sized bag for the specimen. Specimens of 100 mm (4 in.) and 150 mm (6 in.) up to 50 mm (2 in.) in thickness are usually tested with the small bag. Specimens of 150 mm (6 in.) in diameter by 50 mm (2 in.) or greater in thickness will usu
40、ally be tested with a large bag. 6.2.1. Set the heat-sealing bar temperature according to the bag manufacturers recommendations. 6.2.2. Inspect the bag for holes and irregularities, then record the bag mass. Place the bag inside the vacuum chamber on top of the specimen sliding plate. 6.2.3. Insert
41、the specimen into the bag with the smoothest plane of the specimen on the bottom. This operation may be done inside the chamber while holding the bag open with one hand over the sliding plate and gently inserting the specimen with the other hand. There should be about 25 mm (1 in.) of slack between
42、the presealed bag end and the specimen. 6.2.4. If needed, filler plates should be added or removed prior to inserting the specimen. Grab the unsealed end of the bag on each side, and gently pull and center it over the seal bar, overlapping the bag at least 25 mm (1 in.). 6.2.5. Ensure that there are
43、 no wrinkles in the bag along the seal bar just prior to closing the lid. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2c T 331-5 AASHTO 6.2.6. Close the lid, and engage the lid-retaining latch. Th
44、e vacuum pump light will illuminate “red,” and the vacuum gauge on the exterior of the chamber will become active, or a digital reading will show the vacuum state. It is normal for the bag to expand or “puff up” during this process. 6.2.7. Once sealed, the “de-vac” valve will open, and air will ente
45、r the chamber, causing atmospheric pressure to collapse the bag around the specimen. 6.2.8. Disengage the lid-retaining latch, and carefully remove the sealed specimen from the chamber. Gently pull on the bag at any areas that appear loose. Loose areas indicate a poor seal and the process must then
46、be restarted at Section 6.1 with a new bag and a new initial mass. 6.3. Sealed Specimen MassCalculate the mass of the sealed specimen in air by summing the masses recorded in Sections 6.1 and 6.2.2. Designate this mass as B. 6.4. Mass of Sealed Specimen in WaterQuickly weigh the sealed specimen in a
47、 water bath at 25 1C (77 1.8F). Fully submerge the specimen and bag to ensure no trapped air bubbles exist under the specimen. Ensure that the bag is completely underwater and that it is not touching the edges of the water bath. Designate this mass as E. Note 5The time between the lid opening after
48、sealing and the time to placement of the specimen into the water bath should not exceed 1 min to reduce the potential for bag leaks. 6.5. CheckTo ensure a tight seal in the bag, remove the sample from the water, and cut the bag open. Remove the sample from the bag, and determine its mass. Designate
49、this mass as C. Compare this mass with initial dry mass determined in Section 6.1 as A. If A is more than 5 g from the mass of dry specimen C, the results from this method may not be accurate. The check passes if less than 0.08 percent is lost or no more than 0.04 percent is gained. A loss indicates sample material loss, and a gain indicates a possible bag leakage problem. Remove the bag, and restart the process at Section 6.1 if this check fails. 6.6. If the specimen may be needed for referee testing, oven-dry th
