Condensed Silica Fume (Microsilica) in Concrete: Water Demand and Strength Development


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Title: Condensed Silica Fume (Microsilica) in Concrete: Water Demand and Strength Development

Author(s): E.J. Sellevold and F.F. Radjy

Publication: Special Publication

Volume: 79


Appears on pages(s): 677-694

Keywords: compressive strength; concretes; silica; water-cement ratio; water-reducing agents.

Date: 5/1/1983

This paper reports results of a comprehensive invest in the performance of concrete incorporating 8 and 16 % condensed silica fume (mircosilica). Two types of portland cement and one blended cement with 20 % fly ash were used. Two dosage levels of a normal water reducing agent and one for a superplasticizing agent were used. The water demand to produce a 12 cm slump and the compressive strength development of the concretes, were measured. The main conclusions were as follows: The water demand increases with microsilica content when no water reducing agent is used. However, water reducing agents have a greater effect on microsilica concrete than on normal concrete. Thus the water demand for given microsilica content may be controlled to be either greater or smaller than for the reference concrete by adjusting the dosage of water reducing agents. The main pozzolanic contribution to strength develops between 3 and 28 days at 200C. The shape of the 28 day compressive strength vs w/c-ratio curve for a fixed microsilica content is the same as that for the reference concrete, but it shifts to a substantially higher level. The "efficency" of the microsilica in terms of increasing the compressive strength was calculated to be between two and four times greater than that for portland cement.