| Summary: | 碩士 === 逢甲大學 === 土木工程所 === 93 === Concrete is one of the main materials in civil structures. Thus the quality and characteristics of concrete is highly connected to strength of the structure and the life/wealth of its users. In recent years, many researchers have been devoting their efforts to developments of non-destructive methods for testing the quality of concrete in order to find some type of supplement to the destructively drilling and sampling testing method. The purpose of thesis was to apply the indoor velocity measuring system for cylinder specimens developed by our research team to inspect the wave velocity of a self-compacting concrete (SCC) under normal maintenance. Attempts had been conducted to study the relationship between the wave velocity and the age strength of the material on a daily schedule. The future goal of this research is to provide some nondestructive information for precast or drilled specimens so that the technique developed in this study can be applied further to the velocity measuring system for in-situ investigation.
The experimental setup in this study was based on the recommendations from the master thesis of Kuo-Wei Wu: distance between two accelerometers d=9cm, horizontal distance of the seismic source r=11cm, and vertical distances of the seismic source Iy=0.7cm and 7.5cm. Before the experiment, four inspection lines on the side of the SCC specimen were marked in an interval of one centimeter so that accelerometers can be placed correctly on the specimen. During the experiment, a steel ball was used as seismic source by hitting the surface of the specmen in the longitudinal direction. The stress waves generated were measured by two vertical accelerometers mounted on the side of the specimen. The cross-correlation function was used to calculate the cross-correlation wave velocity of the specimen. Finally comparison was conducted between the wave velocity obtained and the compressive strength of the specimen.
Three different stages of experimental plan were conducted in the thesis. The research results showed that: 1. A better vertical distance Iy of the source is 7.5cm, 2. A better time lag to conduct the wave velocity measurement is about 4 hours after taking the specimen out of water for maintenance so that it will have less background noise and the prevention of direct contact of the accelerometers against the residual water on the specimen can be ascertained. 3. The strength-velocity relation function of the SCC was derived by an exponential regression so that a strength prediction formula was obtained. The average error between the predicted strength and the measured strength is in the range of 9.7% when the measured wave velocities were substituted back into the derived formula. This verifies the feasibility of prediction of the SCC strength based on the velocity measured from the system developed.
Keywords: Self-Compacting Concrete (SCC), Age Strength, Cross-Correlation Wave Velocity.
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