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Title: Computer controlled microwave oven system for rapid water content determination
Authors: United States. Army. Corps of Engineers. Ohio River Division.
Gilbert, Paul A.
Keywords: Soil consolidation tests
Soil water content
Soil compaction
Computer controlled equipment
Electromagnetic energy
Microwave oven
Rapid water content determination
Soil mechanics
Soil mechanics instruments
Publisher: Geotechnical Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Technical report (U.S. Army Engineer Waterways Experiment Station) ; GL-88-21.
Description: Technical Report
Abstract: Equipment for determining water content rapidly, accurately, and reliably is required to properly monitor the compaction of earth fills. If the design of a soil structure is based on one set of behavior characteristics but another set is obtained because of improper compaction control, the result can be a structure with performance and maintenance problems over its entire life . Water content may be determined in the conventional oven but this may require up to 24 hr. Under field conditions where large volumes of earth are being placed, real-time water content information is essential because if 24 hr is 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 material. A microwave drying system was developed in this investigation to determine water content reliably and ac6urately in real-time. The design of the system was based on continuously monitoring the weight change of a soil specimen subjected to microwave radiation. An electronic balance was used to monitor weight change in the specimen, and a small computer interfaced with both the balance and a microwave oven in such a manner as to allow software control of the oven in response to specimen water (weight) loss. Theoretical and practical considerations, as well as the equipment and results, leading to the development of equipment are discussed in the study. Although not strictly equipment, the controlling software is an integral part of the system. A source code of this software is included in the study. A variety of soils were tested in the investigation. Comparison of water content determined in the conventional oven with that determined by the microwave system showed agreement, generally, within a few tenths of a percent. The effects of sample size, material plasticity, and particle size are investigated and discussed in the study.
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