| Summary: | 碩士 === 國立中興大學 === 土木工程學系所 === 100 === The purpose of this thesis is to study the relationship between the pulse velocity and compressive strength of fly-ash concrete at various ages. To investigate how the moisture state of concrete affects wave velocity, we establish the relationship between conductivity coefficient and the saturation degree of concrete, and then wave velocity adjustment due to various concrete saturation degrees can be made to accurately predict concrete strength. In this study, ten fly-ash concrete mixture proportions are used to make concrete specimens. The mixture proportions include 15% of fly ash to replace cement, a sand ratio of 45%, two cement paste volume ratios (Vpaste) of 42% and 36%, water-cement ratios of 0.3, 0.4, 0.5, 0.6,and 0.7. The specimens are used to establish the relationship between the UPV velocity and compressive strength. In addition, we also establish the relationship between conductivity coefficient and the saturation degree of concrete. Eventually, these two established relationship curves can be used to estimate concrete strength.
The experimental results show that compressive strength estimated by the measured wave velocity has an error of 30% without considering the effect of moisture content. We measure the concrete conductivity coefficient through the HI-520 water-content meter, and then determine the related concrete saturation degree used to modify the wave velocity. After modification of wave velocity in consideration of moisture content in concrete, the accuracy of the estimated compressive strength is improved significantly. This proves that it is necessary to consider the effect of concrete moisture on wave velocity when the stress wave technique is used to evaluate concrete strength.
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