| Summary: | 博士 === 國立中興大學 === 土木工程學系所 === 95 === The purpose of this dissertation is to investigate the relationship between the ultrasonic pulse velocity (UPV) and the compressive strength of concrete. First, the specimens used in the studies were made of concrete with a paste content of 36% and the constituents of the specimens varied in different water/cement ratios and coarse aggregate contents by weight. Fifteen concrete mixtures were considered and fifteen specimens were constructed for each concrete mixture. 225 (15*15=225) cylindrical specimens were cast and cured in water at 23°C. These specimens were tested at 1, 3, 7, 14 and 28 days. The experimental data were used to establish the relationship between the ultrasonic pulse velocity (UPV) and the compressive strength of concrete.
The experimental results show that the relationship between UPV and the compressive strength of saturated surface-dry (SSD) concrete is significantly influenced by age and coarse aggregate content (CAC). The UPV and the compressive strength of concrete grow with age, but the growth rate varies with mixture proportion. To simplify the analysis task, this study chose hardened concrete (at an age of 28days) as the subject for analysis. It is found that with the same content of coarse aggregate, a clear relationship curve can be drawn to describe the UPV and compressive strength of hardened concrete. This study proposes the UPV and strength relationship curves for concrete having different contents of coarse aggregate. To verify the proposed curves, a verification program was carried out. In this program, additional concrete cylindrical specimens were prepared with change in concrete mixture proportions that include the amount of coarse aggregate (1170, 1040, 910, 780 kg/m3), paste volumes (30%、32%、33%、40%) and water-cement ratios (0.7, 0.6, 0.5 and 0.4). These curves were verified to be suitable for prediction of hardened concrete strength with a measured UPV value and the estimate values just have a relative error within ±10% compared to the actual strength of the cylinders.
In addition, the research also investigates the influence of the fine modulus (FM) of fine aggregate, the surface cleanness of coarse aggregate, the kind of coarse aggregate and the water content of concrete on the correlation between the UPV and the compressive strength of concrete. The experimental results show that the FM of fine aggregate, and surface condition of coarse aggregate have no obvious influence on the relationship between UPV and compressive strength of concrete. However, when the mixture proportions of concrete are the same, the higher UPV the coarse aggregate is, the higher UPV the concrete is. The change of water content of concrete cylinder truly has a significant influence on the UPV of concrete. According to the UPV of the SSD condition concrete cylinders, the UPV reduction can reach 7.5% under oven-dry condition, and reach 4.5% under room-dry condition. It is also found that the UPV reduction decreases with decreasing the water-cement ratio of concrete.
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