Time Domain Reflectometry (TDR) has been gaining rapid acceptance as a technique for measuring volumetric moisture content in pavement systems. TDR probes are increasingly used to determine the effect of variations in moisture content on pavement response. However, in very wet conditions, such as during thawing when excess water from melting ice lenses is entrapped by underlying frozen strata, TDR probes may not be fully reliable. To evaluate the accuracy of both time domain reflectometry and radio frequency moisture probes in seasonal frost areas, the USDA Forest Service (USFS) and the US Army Cold Regions Research and Engineering Laboratory (CRREL) have developed a simple, inexpensive laboratory freeze-thaw moisture sensor testing device.

The device comprises a set of clear plastic rings, 18 inches in diameter, which, when fully assembled, forms a 16 inch high cylindrical chamber that houses both temperature and moisture sensors. A constant water table can be maintained within the instrumented soil sample, thereby allowing moisture to migrate toward the freezing front as the upper boundary cold plate simulates freezing from the pavement surface. The rings allow frost heave to occur as in the field.

The following paper discuses the test procedure and observations resulting from a series of freeze-thaw tests conducted on a sandy silt of varying initial moisture content.

Maureen A. Kestler
USA CRREL
72 Lyme Road
Hanover, NH 03755-1290
Phone: 603-646-4215
Fax: 603-646-4640
E-mail: mkestler@crrel.usace.army.mil