The Modification Of Low-grade Fly Ash And The Application In Concrete

With the rapid development of municipal road and supporting infrastructure in Sichuan province, the premixed commodity concrete is used more and more. Fly ash, as a kind of indispensable concrete admixture, faces severe shortages. Howerver, the circulating fluidized bed of combustion ash (CFBC) in Chengdu area and the low grade common coal-fired boiler fly ash in Panzhihua area were stored outdoors for ages because their properties of high loss on ignition, big water requirement, low activity and poor adaptability of admixture, and that situation has caused some serious resource waste and environmental issues.In order to solve the problem of lack of resources and environmental protection in the two areas, this paper present the modified technique of the two kinds of low grade fly ash, and this study has achieved significant results.Grinding technology and combining with phosphorous slag are effective methods to solve the key problems of those two low grade fly ashes. In this paper, the particle fineness, water requirement ratio, activity index, hydration heat, and the adaptability of admixture of modified fly ash were tested. Besides, the hydration mechanism of phosphorus slag-low grade fly ash composite powders has been explored by microscopic analysis of their hydration products. Finally, the workability, mechanical property and durability of the concrete containing the modified fly ash were studied.The results showed that the grain fineness, water requirement and activity index of those two kinds of low grade fly ash were increased after grinded. By combining with phosphorus slag, the water demand ratio and the hydration heat release rate and hydration heat were reduced appropriately, and the activity index and the adaptability of admixtures were improved obviously. Phosphorus slag mixed with fly ash in panzhihua area has higer degree of hydration than original fly ash, in addtion, its hydration products were increased, and its structure became compact, which benefit the strength of mortar. The two kinds of fly ash inspired their activity each other in the composite system of Phosphorus slag mixed with circulating fluidized bed of combustion ash (CFBC) in Chengdu area, which promoted the secondary volcanic ash reaction and the hydration reaction degree of cement and CFBC. The concrete containing the phosphorus slag with low grade fly ash composite powder were studied, the results showed that the workability was improved dramatically, and there was no bleeding and segregation, what's more, the freezing-thawing resisting performance, the carbonation resistance and the sulfate attack resistance were improved significantly.Phosphorus slag combined with the low grade fly ash was grinded by a certain ratio of the quality, and then they were levigated in size. This composite powder was named as the modified fly ash, which had the lower water demand ratio, the higher activity index, the better adaptability of admixture. According to the national standard GB/T 1596-2005, it could be directly used in common concrete as "?" grade fly ash, whose workability, mechanical properties and the durability is very good.