| Summary: | 碩士 === 國立中興大學 === 土木工程學系所 === 99 === In this thesis, a concrete plate made on construction site was used to conduct a feasibility study of using pulse velocity to evaluate the in-place strength of concrete in consideration of the effect of moisture on strength evaluation. This study established the relationship between pulse velocities and. strength of concrete built up with 18 in-place made φ10*20 cm cylinders. In addition, the study also established the relationship between the conductivity coefficients and the moisture content of concrete from 17 cubes of 15*15*15cm. Through modification of pulse velocity to account for the moisture content of the concrete plates, the pulse velocities measured by ultrasonic tester and impact echo tester (ASTM) were used to obtain predicted strengths which were then compared with compressive strengths of drilled cores of plates. The outcomes of this study indicated that it should be feasible to replace ultrasonic pulse velocity (UPV) with the impact-echo surface P-wave velocity (IEPV) for strength estimation. The results for hardened saturated specimens indicated that the ratio of the surface P-wave velocity to internal ultrasonic pulse velocity is 1. For the hardened concrete, SCC and 420 kgf/cm2-strength concrete rendered similar prediction results. For hardened concrete, the strength prediction errors with UPV were greater than that with IEPV and were mostly overestimated. Possible reasons could be the saturation degrees were rated by conductivity coefficients which had effective depth of 14 mm whereas the thickness of plates was 200 mm, the values of conductivity coefficients only showed the moisture condition on the specimen surfaces. In addition, plates were large specimens in which internal water was not easily lost. So there exists over correction due to the fact that the internal ultrasonic pulse velocity was actually larger than that of the pulse propagating along concrete surface. It can be concluded that the use of moisture-corrected pulse velocity to evaluate concrete strength is only suitable for the IEPV case.
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