1、Standard Practice for Vacuum Drying Compacted Asphalt Specimens AASHTO Designation: R 79-161 Release: Group 3 (August 2016) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-2c R 79-1 AASHTO Standard Practice for Vac
2、uum Drying Compacted Asphalt Specimens AASHTO Designation: R 79-161Release: Group 3 (August 2016) 1. SCOPE 1.1. This standard practice covers the process of drying compacted field and laboratory specimens using a vacuum apparatus. The values stated in SI units are to be regarded as the standard. 1.2
3、. The specimens dried by this practice remain at close to room temperature, which helps in maintaining specimen integrity during the drying process and allows the operators to run repeated tests on the same sample, if necessary. 1.3. This standard can also be used for drying other construction mater
4、ials such as concrete, soils, aggregates, and loose asphalt mixtures. Use recommendations provided from the manufacturer for drying other construction materials. 1.4. This standard practice may involve hazardous materials, operations, and equipment. This standard does not purport to address all of t
5、he 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 2.1. AASHTO Standards: M 231, Weighing Devic
6、es Used in the Testing of Materials T 168, Sampling Bituminous Paving Mixtures 3. TERMINOLOGY 3.1. constant massthe mass at which further drying does not alter the mass by more than 0.05 percent when weighed at 2-h intervals using oven drying at 52 3C (125 5F). 3.2. dry specimen conditiondry specime
7、n condition is based on the factory calibrated pressure at which no more water remains in the vacuum chamber. 4. APPARATUS 4.1. Vacuum DeviceAttached to a pump capable of evacuating a sealed chamber to a pressure of 6 mmHg when at sea level. The chamber shall accommodate cylindrical specimens of 150
8、-mm diameter by 180-mm height or cubical samples of 150-mm length by 150-mm width by 180-mm height. 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2c R 79-2 AASHTO 4.1.1. The device shall be capable
9、 of controlling the vacuum, airflow, and temperature in order to properly dry the specimen at close to room temperature. 4.1.2. The device shall display a pressure value that indicates a dry point in the chamber and number of cycles. 4.1.3. The device shall have a plate for removing water from the b
10、ottom surface of the specimen chamber. 4.1.4. The device shall have a means to trap moisture that is removed from the sample. 4.2. A handheld infrared temperature sensor accurate to 5C (9F) shall be used to measure surface temperature of the specimens. 4.3. Weighing DeviceThe weighing device shall c
11、onform to the General-Purpose Balances and Scales, Class G 2 requirement of M 231. 5. PROCEDURE 5.1. Specimens shall be kept and stored at temperatures above 15C (60F). 5.2. Plug the unit into a power outlet and turn on the switch. Note 1Keeping the unit in the off position when not in use can prolo
12、ng the operating life of the components used in the vacuum drying device. 5.3. Dry the moisture trap (if necessary) and the specimen (vacuum) chamber. Run the unit without any specimens. The unit should display a pressure value that indicates a known dry point. If the unit fails to achieve a dry poi
13、nt pressure value, as recommended by the manufacturer, check that the lid and all hose connections are well sealed. If needed, refer to the manufacturers troubleshooting instructions. 5.4. Measure the sample temperature with a handheld infrared thermometer. Make sure the specimen temperature is abov
14、e 15C (60F). 5.5. Remove any standing water from the surface of the specimen by using a paper towel or an absorptive cloth. 5.6. Place the specimen inside the vacuum chamber. 5.7. Place lids on the vacuum chamber and moisture trap (if applicable). Press “Start” to begin the drying process. 5.8. The
15、machine will automatically stop when the specimen is dry. The unit shall be calibrated at the factory or by the operator to sense a “dry specimen condition.” The pressure is monitored throughout the drying process to ensure “dry specimen condition” pressure is achieved in the unit. Note 2Sample is c
16、onsidered dry when the measured weight after vacuum drying process is within 0.1 percent or less of 24-h oven drying at 50C. This check is only recommended when verification of drying performance is needed. 5.9. Between drying specimens, if applicable, wipe off any free-standing water in the moistur
17、e trap. This will speed up the specimen drying process. 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-2c R 79-3 AASHTO 6. KEYWORDS 6.1. Constant mass; drying; drying apparatus; moisture trap; vacuum drying. 1Formerly AASHTO Provisional Standard PP 75. First published as a full standard in 2016. 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.
