Sample Conditioning for Testing

Both ASTM and AASHTO recognize the importance of proper sample handling to achieve valid test results. They recognize that all asphalt emulsions are made hot typically 180° to 200° F (82° to 93° C), some grades are stored hot typically 150° to 180° F (66° to 82° C), and that some of these hot stored grades are subsequently transported and applied at temperatures above 140° F (60° C). Hot samples collected in the field usually arrive at the laboratory at ambient temperature. How should these samples be handled? The language in ASTM D244 and AASHTO T-59 is significant and similar, with AASHTO stating:

All emulsions with viscosity requirements of 50° C (122° F) should be heated to 122 5° F (50° 3° C) in a 160° F (68° C) water bath or oven. The container should be vented to relieve pressure. After the sample reaches 122 5° F (50°3° C), stir the sample to achieve homogeneity.

The above statement recognizes that the viscous grades of emulsion, those tested for viscosity at 122° F (50° C), generally give low, false viscosity values if manipulated or handled in the laboratory at ambient temperatures. The key to this sample-conditioning step is that if the sample is NOT stirred or agitated prior to heating to 122° F (50° C), it will give a more realistic laboratory viscosity like that experienced at the jobsite. This recovery of the jobsite viscosity is quite independent of the duration of ambient temperature storage of the sample.