Using Medium- to High-Volume Fly Ash Blended Cements to Improve the Sulfate Resistance of High-Lme Fly Ash Concrete

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Title: Using Medium- to High-Volume Fly Ash Blended Cements to Improve the Sulfate Resistance of High-Lme Fly Ash Concrete

Author(s): J. R. Prusinski and R. L Carrasquillo

Publication: Special Publication

Volume: 153

Issue:

Appears on pages(s): 43-66

Keywords: blended cements; chemical attack; durability; expansion; fly ash; lime fly ash; sulfate attack; sulfate resistance; Materials Research

Date: 6/1/1995

Abstract:
Concrete placed in contact with a sulfate environment can severely degrade due to formation of expansive compounds such as ettringite. The use of low-calcium fly ashes in concrete have been successful in mitigating these expansions. However, some high-calcium ashes have the potential to cause increased expansion of the concrete, leading to accelerated deterioration. This research focuses on producing cements interground with Class C fly ash, which can be used to produce sulfate-resistant concrete. ASTM Type I and Type II cements were blended with a sulfate-susceptible Class C ash in amounts from 0 to 70 percent fly ash. Concrete was produced using a standard Texas Highway Department 306 kg/m 3 mixture and the various interground and unblended cements. Specimens were soaked and monitored monthly for 3-1/2 years in a 10 percent sodium sulfate solution to accelerate sulfate attack. Results indicate that certain specimens made with interground cements having fly ash contents between 25 and 70 percent, and additional blended gypsum, achieved lower expansion than control specimens made with Type II, Type V, or 0 percent C 3A cements alone. This was true for fly ash/cement blends using both Type I and Type II cements. Compressive strengths of the fly ash blends, through 365 days, attained levels generally comparable to, or better than, the controls.