Tube Suction Test for Evaluating Aggregate Base Materials in Frost- and Moisture-Susceptible Environments

Abstract

A simple tube suction test has been developed by the Finnish National Road Administration for evaluating unstabilized granular base material. The test consists of monitoring the capillary rise of moisture within a 150-mm-diameter by 200-mm-high cylinder of compacted aggregate. A probe is used to measure the dielectric constant at the surface of the sample. The dielectric constant is a measure of the free, or unbound, water within the aggregate sample. It is this unbound water that is thought to be directly related to the strength of the material and its ability to withstand repeated freeze-thaw cycling. Measurements of dielectric constants are made over a period of 10 days. The poorest performing materials are those that rapidly reach saturation and exhibit high surface dielectric values. A study was conducted on four marginal aggregates from Alaska, Nevada, New Mexico, and Texas. These aggregates have been reported to be poor performers in their environments. Each aggregate failed the tube suction test. A mineralogical evaluation was performed to identify the mineral composition of each aggregate and to explain their high affinity for moisture. Subsequently the aggregates were treated with a concentrated liquid stabilizer. Upon treatment the aggregates showed improved performance in the tube suction test. The Alaska, Nevada, and New Mexico aggregates were then used in construction projects. Initial performance reports have been promising. The tube suction test described in this research has the potential to identify moisture-susceptible aggregates and to serve as a guide in selecting the optimal stabilizer type and amount.