Mix Proportions and Strength Characteristics of Concrete Containing 50 Percent Low-Calcium Fly Ash

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Title: Mix Proportions and Strength Characteristics of Concrete Containing 50 Percent Low-Calcium Fly Ash

Author(s): R. N. Swamy and H. B. Mahmud

Publication: Special Publication

Volume: 91

Issue:

Appears on pages(s): 413-432

Keywords: compressive strength; concretes; curing; flexural strength; fly ash; high-strength concretes; mix proportioning; modulus of elasticity; plasticizers; stress-strain relationships; tensile strength.

Date: 2/1/1986

Abstract:
Data on the mix design, strength and elasticity properties of concrete containing 50% low calcium fly ash replacement and a superplasticizer for 28 day strengths of 20 to 60 MPa are presented. It is shown that for concretes with low water-cement ratios of 0.32 to 0.42, high early strength of 12 to 20 Mpa in one day and 28 day strengths of 45 to 60 MPa can be produced with slumps in excess of 150mm. Under wet curing such concretes can give strength increases of 50 to 100% from 28 days to one year compared to increases of 18 to 25% for all OPC concretes. Even under the worst curing conditions, fly ash concretes showed a slow but steady strength gain and maintained their target strengths at one year whereas all OPC concretes under similar conditions showed strengths of 25 to 35% below the target strength. Air drying always produced greater losses in strength and elasticity in all OPC concretes than in fly ash concretes. The latter were able to develop flexural strengths of 3.5 to 6.0 MPa and tensile splitting strengths of 2.0 to 4.5 MPa at one year under these conditions. The practical and technical benefits of incorporating high fly ash contents are emphasized.