Rapid Water Content by Computer‐Controlled Microwave Drying

Equipment for determining water content rapidly, accurately, and reliably is required to properly monitor the compaction of earth fills. Improper compaction control can result in structures with severe performance and maintenance problems. Water content determination in a conventional oven may require up to 24 hr. If 24 hr are required to determine that the water content of a layer is unacceptable, that layer may be buried under several feet of subsequently placed and compacted fill. This paper describes a microwave drying system developed to determine water content reliably and accurately in real time. The design of the system is based on continuously monitoring the weight change of a soil specimen subjected to microwave radiation. The system, its theory of operation, and its use are described briefly. Data are presented to show that microwave and conventional water contents usually correlate to within half a percentage point for a variety of soils. The microwave system has been satisfactorily used on two Corps of Engineers filed projects. Analysis of data from the projects is presented.