DEVELOPMENT OF SMALL EMBEDDED GAUGE FOR CONCRETE

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It is very common to measure the strain of material when clarifying it's mechanical properties. For concrete specimen, the adhesive-bonded strain gauge is generally used, and in the strength tests, the measurement using strain gauge is comparatively easy. However, in the long term test (for instantce, the drying shrinkage and creep test) , the measurement of time-dependent strain is difficult because the matrix of gauge (polyester) is corroded by the alkalinity of cement, and then the gauge has a very poor electrical insulation. To solve this problem, the use of the embedded gauge is best. Presently, the embedded gauge is commercially available, but it's size is a little large and the price is very expensive.This research project was designed to develop the small embedded strain gauge for cement paste, mortar, and concrete specimen. The engineering plastic (PPS) was selected as the material of gauge because of the excellence of it's water and chemical resistance and it's mechanical behavior. The dumbbell shape small embedded gauge with the diameter of 4 mm and the length of 30 mm and 60 mm was developed. In order to evaluate the performance of the embedded gauge, both compressive and direct tensile strength test at the age of 1,3,7,28,180days and 1 year, and the drying shrinkage and creep test of 1-year period were carried out. For the comparison of the strain measured, the adhesive-bonded strain gauge, compressometer, and contact gauge were used. It was found that the measurement using the small embedded gauge was available, and especially in the long term-test, the very stable strain was obtained, although the evaluation of it's gauge factor should be considered in the future.