Silica Fume Concrete to High-Strength Precast Prestressed Highway Bridge Girders

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Title: Silica Fume Concrete to High-Strength Precast Prestressed Highway Bridge Girders

Author(s): Colin D. Johnston

Publication: Special Publication

Volume: 114

Issue:

Appears on pages(s): 1077-1100

Keywords: bridges (structures); compressive strength; costs; girders; high-strength concretes; plasticizers; precast concrete; silica fume; prestressed concrete; Materials Research

Date: 5/1/1989

Abstract:
Mixtures employing silica fume (SF) and superplasticizers with a worst-case combination of the available local gravel and cement sources were evaluated using 250 to 500 kg/m3 of Type I cement instead of Type III, and up to 15 percent silica fume. Many of the mixtures evaluated met or substantially exceeded the specified strength criteria at a cost below that of the concretes presently used. Hardened concrete air void parameters are also satisfactory for the SF concretes examined. A mixture using 300 kg/m3 of Type I cement with 10 percent SF comfortably met the present strength specifications at considerably reduced material cost when using accelerated curing. However, 20-hr strengths of 45 to 50 MPa and 28-day strengths over 50 MPa are possible with higher cement contents. A mixture using 450 kg/m3 of Type I cement with 10 percent SF can just meet the 20-hr strength requirement without accelerated curing, and its 28-day strength exceeds the current specification requirement by more than 50 percent. Slightly lower material costs and the saving associated with eliminating accelerated curing coupled with long-term strength in excess of 60 MPa make this concrete attractive in terms of both cost and strength if designers can fully utilize the higher strength.