- Q. We are about to begin a large project that will require our technicians to take hourly field test samples of the fine materials. We’ve started to investigate alternatives to our normal oven-drying procedures. One method we recently discovered is vacuum drying. Do you know anything about this material drying procedure and system?
A. While there has been a great deal of research on microwave drying of aggregate samples, there’s interest in a new drying process. InstroTek (www.instrokek.com), a Raleigh, N.C., material testing equipment manufacturer, has developed a device that vacuum dries aggregate samples. The CoreDry unit is portable, compact, and can easily be set up to fit in tight on-site applications.
The device combines a new vacuum technology with electronic desiccation. Samples are cycled through flows of ambient air and vacuum processing. As water is attracted to the sample’s surface, the chamber’s lower pressure causes the water to quickly evaporate at room temperature. At the end of each vacuum cycle, any moisture removed is captured in an electronic trap for weighing
The CoreDry device can dry samples of up to 600 grams, using a specially fabricated aggregate container. Sample weights of 400-500 grams are ideal for quick aggregate moisture determinations. “For fine aggregates, if very quick results are required, the sample size can be reduced to 150-250 grams,” says Emil Albouyeh, one of the device’s developers.
Using this moisture extraction system, the CoreDry will dry samples at a rate of 1.5 grams of water per minute. An aggregate sample that contains 10 grams of water will take about 15 minutes.
Albouyeh has compared test data from the vacuum drying process to conventional oven drying. The vacuum drying time of both aggregate and sand are slightly faster than oven drying because oven drying of sand and aggregate uses high temperatures.
Several DOTs are currently testing the vacuum technology to test for aggregate and soil moisture content. Currently, a standard is under review by an ASTM committee and should be completed soon. However, the use of the machine is permitted as most current standards specify drying the samples to constant weight, which can be accomplished with the testing device.
The unit was specifically developed for quick drying of construction materials. But the vacuum drying process is very versatile. “We are working with the labs that test the moisture content of wood chips for pulp and paper manufacturers and from agronomists who want to determine moisture content of seeds,” says Albouyeh.