Study On The Effect Of Mixing Method On The Air Content And Performance Of Concrete

In the project application, the concrete must have good durability.The frozen and meltingcycle will lead the intensity of the concrete’s structure to decrease, which will significantlydecrease the durability of the structure of the concrete. The key component of good durabilityis good frost resistance. By bringing in proper air content, the usability, durability (frostresistance) and impermeability can be greatly improved. The air entrainment technologydeveloped in30thof the last century is one of the greatest progress in the development of theconcrete technology. Air-entraining concrete has been used in almost all the structures of thearchitectures. People widely add air-entraining agent in order to improve the air content of theconcrete in project. There’re many factors affecting the air content of the concrete. Thestudies aimed at material graduation, slump and water cement radio etc have been carried outat home and abroad. However, few studies have aimed at the effects of the mixing process onconcrete air content. As the most basic preparation method, if we take the method of mixingto improve the air content of the concrete, it will be more inexpensive and convenient.In this dissertation, the effects of normal forced mixing method and several vibrationmixing methods on the durability and air content of concrete were researched based on themixing conception and vibration mixing theory, with the vibration stirring prototypes of singlehorizontal shaft, double horizontal shaft and vertical spindle shaft as experimentalplatforms.The dissertation studies the factors affecting air content of the concrete in themixing process and its regulation. We mainly studies the effect of the mixing parameters(amplitude, vibration frequency, mixing speed, setting angle of mixing blades, etc.) on aircontent of the concrete. By testing and analyzing concrete’s air content and concrete strengthwhich is obtained in different mixing conditions and mixing parameters, the proper excitationsource position in the vibrating mixing method and the effect of the vibrating mixingparameters on the concrete’s air content were studied, and the effect mechanism was analyzedand compared. What’s more, we compare the vibrating mixing method with the widely usedtechnology of air-entraining agent. By using the electronic microscope photograph andmercury poromesitry, we analyze the microscopic structure of the concrete in various mixingconditions and their relations. Besides, the microscopic principle of the macro properties has been analyzed.The result indicates that beside the widely used technology of air-entraining agent, theproper mixing method with proper mixing parameters which means the mixing blade alsoserves as excitation source can significantly improve the concrete’s air content. By choosingthe proper vibrating mixing method, the concrete’s air content can averagely reach about3.5%,which meet the requirement of the frost resistance in the project. Such concrete has relativelyhigh pressure resistance at the same time. When we combine the technology of air-entrainingagent and vibrating mixing method, we can gain higher air content. Besides, these twomethods complement each other’s advantages on improving the structure of the pore. By theanalysis of the microscopic principle, it indicates that the vibrating mixing can promote theimprovement of the microstructure of the concrete’s transition layer and cement’s hydrationslurry, and it can improve the pore distribution of concrete, that results in improving thestrength and durability of the concrete.The research dissertation was financed by the National Natural Science Fund Project（50678026）.