The Tube Suction Test was developed by Saarenketo and Scullion at the Texas Transportation Institute (TTI) for investigating the suction properties of various base course aggregates, and has been further tested and developed during 1996-2000 at TTI, the Tampere University of Technology, in the laboratory of the Lappi Region of Finnra, and at the University of Saskatchewan.
The research results show, that the suction properties of base aggregates have a very significant effect on the deformation properties of the base course. Suction properties, in turn, are primarily dependent on fines content, but also on the chemical properties of the aggregate. The Tube Suction Test takes into consideration matric suction and osmotic suction, as well as the effect of material density on water flow.
The Tube Suction Test has proved to function well in the identification of problematic aggregates as well as in defining appropriate binder types and their required amounts.
During the Tube Suction Test, base aggregate samples (# 0-18mm) are compacted at optimum moisture with a gyratory compactor (ICT) into a 305 mm high and 152 mm diameter plastic tube. The height of the sample should be 180-200 mm. After compacting, a perforated cover is placed on the bottom of each tube, and the samples are dried in an oven at 45 °C, until no more significant changes are observed in their weight. After oven drying, the samples are allowed to cool down at room temperature for at least two days. When their temperature has stabilised, the samples are placed in a dish containing approx. 20 mm of deionised water.
The first measurements of the dielectric and electrical conductivity values are taken before placing the tube samples into the water. Once in the water, measurements are taken at 2 h intervals during the first day, in addition to an initial reading which should be taken a half-hour after placing the tube samples in the water. From the second day on, only one measurement is required per day (in the morning), until the weight of the samples and the dielectric values become constant. The weight of the tube samples is measured in connection with every dielectric value measurement. Grain size, surface moisture content (5 cm), specific density and other required parameters are measured from the samples after the test.
The test can be conducted in the same way for bound and unbound aggregates
See demo of the Tube Suction Test.