Determining Aggregate Frost Susceptibility with the Tube Suction Test

Abstract

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 aggregate base materials. The moisture susceptibility ranking is based on the mean surface dielectric value of compacted specimens after a 10-day capillary soak, where the dielectric value is most sensitive to the amount of unbound water that exists within the aggregate matrix. The purpose of this research was to investigate the relationship between the final dielectric value in the TST and the frost susceptibility of aggregates. The laboratory test program included 35 specimens representing 10 aggregate base materials from Indiana, Minnesota, Pennsylvania, Texas, and Virginia. Each sample was subjected to the TST and afterwards to a frost heave test developed at TTI. In the TST, electrical conductivity measurements were also made to evaluate the salinity of the specimens. Sample volumetrics were computed and compared for post-TST and post-freezing conditions. In this study, aggregates classified in the TST as good performers did not experience significant frost heave, while several materials with higher dielectric values exhibited substantial amounts of heave. These latter specimens were characterized, on average, by greater percentages of fines, higher porosity, and higher moisture contents in the TST. Aggregate samples with high salinity also had high dielectric values in the TST, but they were generally less frost susceptible than other high-dielectric specimens due to the depression of the freezing point caused by salt ions in the pore water. Samples with high porosity also exhibited reduced frost heave because the additional internal space allowed formation of ice with less expansion of the aggregate matrix.