| Summary: | 碩士 === 國立屏東科技大學 === 土木工程系碩士班 === 94 === The thesis studies the feasibility of prestressed box-girder using the impact-echo method to evaluate the quality of slabs by measuring the pressure wave velocity of concrete. The L-shape specimens were made to perform tests to imitate the shape of the corner between the bottom and side slabs of box-girder cross section. Firstly, the suitable impacting steel ball for slab thicknesses was tested; then, the influences of the conduct and the corner on measured velocity values were discussed. The results are then compared with those measured by the direct measurement using ultrasonic device.
The test results showed that, diameter 5 mm or above of steel ball must be used for the thickness of bottom-slab about 20 cm, and 13 mm or above must be used for use the thickness of the side-slab about 30 cm. For the measured points on side-slab with a conduct of 10 cm diameter inside, the wave velocity value measured by the ultrasonic device was not changed much, but was decreased 15~28% with average 20% by the impact-echo method. On the place without conduct, the test results by the impact-echo method were very close to those by the ultrasonic device. The errors were within ±10%, most of them within ±5%, and average errors was about ±1%. On the corner area, the variation of the wave velocity measured by the impact-echo method was large. When compared with those by the ultrasonic device, the values were too high with average error 7.4% for using steel ball as impact, and too low with average error -33.3% for small hammer. Therefore, the result of wave velocity measured by the impact-echo method was not good on the corner area.
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