NISHIKATA¡¡Tomohiro
Study on the evaluation of concrete structures performance by the measurement of unit water amount
MARUYAMA¡¡Kyuichi
In order to make strong and durable concrete structures, ensuring the quality of the concrete is important. It is generally assumed that the quality of concrete is spatially uniform in the concrete design. However, the spatial variation of concrete quality may occur by various factors.
In this research, the possibility of evaluation and the control of variation of the quality of concrete were studied using a unit water amount measuring instrument.
I carried out a performance test of the instrument prior to the study by making various types of mortar. Test factors are unit water amount, water-cement ratio, cement type, mortar temperature, elapsed time, and etc.. By comparing these results with the concrete design values, the accuracy of instrument is verified. Then with this results and using the unit water amount, it is possible to approximate the water to cement ratio which is representative factor of the total quality of concrete. Thus, this instrument was used in this research.
In order to investigate the spatial variation of concrete quality inside a concrete truck, samples of concrete were taken during unloading fresh concrete from a truck, unloading it in 3 phases. In each phase, 3 samples were taken and, unit water amount and the amount of coarse aggregate were measured in each sample.
Furthermore, a specimen of concrete was built and the quality variation caused in steel concrete cover was evaluated. The influence of mix composition on the spatial variation is studied in this test.
The obtained results indicates that when the concrete is unloading from the truck, the early unloaded part has a more coarse aggregate than the latest unloaded concrete part because of the segregation occurrence of coarse aggregate and mortar when concrete is stirring inside of the truck. Besides, the results obtained from the built specimen of concrete confirmed that the amount of unit water in upper layers is higher than that of lower layers due to segregation, and the mix composition affects the magnitude of this variation.
Thus, it was confirmed that the concrete quality is able to be evaluated by measuring the unit water amount.
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