AASHTO R79-19 pdf free download

AASHTO R79-19 pdf free download.Vacuum Drying Compacted Asphalt Specimens.
3 TERMINOLOGY
3.1. diy specimen condition—dry specimen condition is based on the factory calibrated pressure at
which no more water remains in the vacuum chamber.
4. APPARATUS
4.1. Vacuum Device—Attached to a pump capable of evacuating a sealed chamber to a pressure of
6 mrnHg when at sea level. The chamber shall accommodate cylindrical specimens of 1 50-mm (5.91 -in.) diameter by I 80-mm (7,09-in.) height or cubical samples of 150-mm (5.91-in.) length by 150-mm (5.91-in.) width by 180-mm (7.09-in.) height.
4.1.1. The device shall be capable 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 bottom 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 thermometric device accurate to ±5°C (±9°F) shall be used to measure surface temperature of the specimens.
4.3. Weighing Device—The weighing device shall conform to the General-Purpose Balances and Scales, Class G 2 requirement of M 23 1.
5. PROCEDURE
5.1. Specimens shall be kept and stored at temperatures above 15°C (60°F).
5.2. Plug the unit into a power outlet and turn on the switch.
Note 1—Keeping the unit in the off position when not in use can prolong 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 point pressure value, as recommended by the manufacturer, check that the lid and all hose connections are well sealed. If needed, refer to the manufacturer’s troubleshooting instructions.
5.4. Measure the sample temperature. Make sure the specimen surface temperature is above 15°C
(60°F).
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). Initiate the vacuum drying process.
5.8. The 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 2 —The sample is considered dry when the measured weight after the vacuum drying process is within 0.1 percent or less of 24-h oven drying at 50°C (122°F). This check is only recommended when verification of drying performance is needed.
5.9. Remove the specimen from the chamber. Determine and record the specimen mass to the nearest
0.1 g.
5.10. Repeat Sections 5.6 through 5.8.
5.11. Remove the specimen from the chamber, Determine and record the specimen mass to the nearest
0.1 g. Compare this value with the mass obtained in Section 5.9. If the mass determinations vary by more than UJ g, repeat Sections M through .9 until the mass values from consecutive drying cycles are within 0.3 g of each other.
5.12. Between drying specimens, wipe off any free-standing water in the moisture trap. This vi11 speed up the specimen drying process.
6. KEYWORDS
6.1. Drying; drying apparatus; moisture trap; vacuum drying.AASHTO R79-19 pdf download.