Abstract: Based on the background of an expressway project in Guizhou province, an experimental investigation on mechanical sand C50 concrete prepared by high frequency vibration was carried out in the construction site laboratory. The main raw materials are selected in test and their performances are tested and optimized to determine the best mixing ratio of the C50 machine-made sand concrete. The compressive strength and durability of the C50 machine-made sand concretes prepared by different stirring methods are tested and compared with each other. The compressive strength and durability of C50 sand concretes prepared by different stirring methods were tested and compared further, and internal microstructures of C50 sand concretes prepared by different stirring methods were observed one by one by industrial CT scanning. Tested results indicate that the high-grade concrete of machine-made sand may be prepared by using the special high-frequency vibration mechanism. Compared with the ordinary self-falling machine-made sand concrete, it is found that the performance of the concrete prepared by high-frequency vibration is higher than that of the concrete prepared by ordinary stirring. The compressive strength and durability of the concrete are improved therefore. The internal structure of the machine-made sand concrete prepared by high-frequency vibration stirring becomes more compact and uniform, and the integrity of the concrete is better as a result.

Key words: machine sand, C50 concrete, high frequency vibrating mixer, compressive strength, durability, CT scanning