Effect of Cement Replacements by Fly Ash and Silica Fume on Compressive Strength of Concrete


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Title: Effect of Cement Replacements by Fly Ash and Silica Fume on Compressive Strength of Concrete

Author(s): L. V. A. Seshasayi, D. Ramaseshu, Svnopsis: and R. Shankaraiah

Publication: Special Publication

Volume: 199


Appears on pages(s): 581-594

Keywords: compressive strength; fly ash; high performance con-crete; high strength concrete; silica fume

Date: 6/1/2001

In developed countries use of mineral admixtures such as fly ash, silica fume has already been adopted in making concrete. This includes commercial application on a large scale either for addition or for replacement of cement. In India too such replacements have been readily accepted. With the introduction of ready mixed concrete the process has been accelerated in recent times. An investigation was undertaken to study the effects of fly ash and silica fume in concrete. Compressive strengths at different levels of replacements were found. Silica fume from a local source and fly ash from Ramagundam thermal power station of the State of Andhra Pradesh were used. Maximum size of coarse aggregate was 12.5 mm. Water to cementious materials ratio was 0.32 and aggregate-cementitious materials ratio was 3.2. Cement replacement levels by fly ash were 0, 10, 20, 30, and 40 percents and by silica fume were 0,4, 8, 12, and 16 percents. Thus a total of 25 mixtures were studied. Strengths at the ages of 28 days and 56 days were found. The results are presented in tables and figures. It was found that the highest replacement level of 40 % by fly ash and 16 % by silica fume, simultaneously, i.e. a total replacement of cement to the extent of 56 % gave a 10 % increase in the 28-day compressive strength compared to that of control concrete. Maximum increase of 43 % in the 28-day compressive strength was observed at a 32 % level of cement replacement ( 20 % by fly ash and 12 % by silica fume).