Interlaboratory Study of the Tube Suction Test (0-4114-2)

The Tube Suction Test (TST) was developed in a cooperative effort between the Finnish National Road Administration and the Texas Transportation Institute (TTI) for assessing the moisture susceptibility of granular base materials. The moisture susceptibility ranking is based on the mean surface dielectric value of compacted specimens after a 10-day capillary soak in the laboratory, where the Adek PercometerTM is employed in the test to measure the dielectric values of specimens. Based on promising correlations of test results to important engineering properties of aggregates, this project was initiated by the Texas Department of Transportation (TxDOT) to conduct an interlaboratory study aimed at developing a standard test procedure and a precision statement for the TST. The project involved six TxDOT district laboratories geographically distributed across the state. The repeatability limits computed from data obtained in this project compared well with those repeatability limits calculated from data collected in earlier research, which were also used to demonstrate that the repeatability limits are proportional to the final dielectric value. The reproducibility limits obtained in this project exceeded the repeatability limits by factors as high as four and were the motivation for further testing. Relative humidity was shown to have major impacts on the final dielectric values of specimens tested in the TST, and the protocol was subsequently revised to require capillary soaking inside a closed ice chest. However, inconsistencies between different PercometerTM devices may also have been the source of the poor reproducibility observed in the study. This report provides background information about the development of the TST, presents the details of the interlaboratory study, summarizes findings, and offers recommendations for further work. NOTE: Report 0-4114-1 was not published and contains no information not in 0-4114-2.