The shrinkage limit of cohesive soils is defined as the water content at which further loss of moisture will not cause a decrease in volume. ASTM recommends this new method as an alternative to the original D 427 test method, which was withdrawn due to its use of mercury for volume determinations. This procedure uses similar apparatus for preparation of a soil pat, but requires immersion of the pat in melted wax. This step prevents absorption during a subsequent immersion in water for mass determination.
Samples for shrinkage limit tests are usually taken from a larger sample prepared for liquid and plastic limit tests. A soil specimen with moisture content above the liquid limit is placed in the shrinkage dish and struck off with the straightedge. The sample is then oven dried. After coating in wax, volume of the soil pat is computed by weighing in water and noting the difference from its weight in air.
The Shrinkage Limit Set includes a special Monel shrinkage dish, a metal straightedge, fine thread to suspend the soil pat, a glass calibration plate and a tube of petroleum jelly, used when calibrating the dish.
Meets Test Method:
ASTM D 4943