U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
|This report is an archived publication and may contain dated technical, contact, and link information|
Publication Number: FHWA-04-111
Date: February 2005
The NCHRP 9-10 researchers used three sampling times (6 hr, 24 hr, 48 hr) and in the present study, four sampling times (6 hr, 24 hr, 31 hr, 48 hr) were used. While these are acceptable during procedure development, they are not convenient for use during routine testing in practice. Therefore, to shorten the test, it is recommended that sampling be done only at 0 hr and 48 hr. This, however, does not guarantee that the conclusions drawn would always be accurate.
In fact, based on the results obtained for the modified binders analyzed in this study, the LAST cannot be truly termed a reliable test. On a number of occasions, the samples that failed the Rs or Rd criterion in the first instance passed when reruns were performed. This implies that the results based on the LAST cannot always be trusted to be accurate enough to judge the stability of the modified binders.
The test itself is very time-consuming, and too much care must be taken to make sure that the time of drawing of samples matches with the time when the DSR would be available to generate rheological data. If there are delays, then the results cannot be trusted, due to the effect of an extra time variable that has crept into the experimental plan.
To generate rheological data for the LAST, the DSR was locked in for extended periods of time due to the nature of the sampling conditions. However, there might be a way to circumvent this problem. In almost all cases, because the variation in the phase angle d at different time intervals is marginal, one possibility would be to track the stability of the samples through devices other than the DSR, namely, viscometers that could assess only the viscous property; they should be able to assess the stability with equal efficacy.