| Summary: | 碩士 === 國立屏東科技大學 === 土木工程系所 === 102 === The thesis designed concrete of six different nominal compressive strength fc of 175、210、245、280、315、350 kg/cm2. Three ψ15×30 cm cylindrical specimens were made for each kind of strength to perform the 28th day concrete compression testing. Additionally, a 50×10×10cm concrete specimen was made for each kind of strength to be measured the P-wave velocity CP and R-wave velocity CR of concrete specimen using the surface measurement by the impact-echo method and the improved ultrasonic pulse-wave method. The Rayleigh equation and the relationships between material properties were then employed to calculate the S-wave velocity CS, the dynamic modulus of elasticity Ed and the dynamic Poisson ratio νd. Finally, regression analysis of fc vs Ed, fc vs Ed and ρ, fc vs CP was performed on the six concrete specimens of different compressive strength to find a best strength estimating formula.
The test results show that, the correlation of the regression equation of the improved ultrasonic pulse-wave method is better than that of the impact-echo method due to the poor correlation of CR vs fc measured by the impact-echo method. Among the three types of regression equations, the best is fc vs CP, fc vs Ed is the second, fc vs Ed and ρ is the worst. Therefore, the thesis proposes that: if CP can be measured by opposite faces, the regression equations fc = 5.39×10-5Cp2-0.160Cp or fc = 6.62×10-14Cp4.31 can be used; If only the surface measurement can be used by the impact-echo method, the regression equations fc = 5.00×10-4Cp2-0.131Cp or fc = 2.14×10-12 Cp 3.92 can be used; If only the surface measurement can be used and an ultrasonic device can be used as the wave source, the improved ultrasonic pulse-wave method can be employed to measure, you use be ultrasonic pulse-wave method to measured, the regression equations fc = 5.47×10-5Cp2-0.150Cp or fc = 5.79×10-13Cp4.07 can be used. The correlation coefficients r of the above regressions are above 0.96. Their correlations are very good
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