Evaluation of the Characteristics of Silica Fume for a Concrete Admixture

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Most of silica fume used in Japan are imported silica fume.As very small amount of silica fume is produced in Japan, it is expected silica fume concrete to be high (or very high) performance concrete in Japan. It means that silica fume concrete should have many good properties such as high strength, high durability and high workability. So, it is necessary to know which characteristics of silica fume relates to the properties of concrete.The purpose of this research program is to find out the influence of the characteristics of 13 kinds of silica fumes, which were on the market in Japan during 1991-1992, as concrete admixtures considering. Through this study, following conclusions were clarified ;1) There are some correlations among physical and chemical properties of silica fume, such as correlation between siO_2 and alkali content.2) Early hydration of cement paste was accelerated by using silica fume.3) W/C,moisture content and SiO_2 content of silica fume are the two main factors on compressive strength of concrete containing silica fume. But the effect of superplasticizer was very strong.4) Reducing effect of silica fume on the concrete expansion due to A.S.R.(Alkali-Silica Reaction) could be evaluated by alkali content of silica fume.