Concrete Incorporating High-Volume of ASTM Class C Fly Ash With High Sulfate Content


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Title: Concrete Incorporating High-Volume of ASTM Class C Fly Ash With High Sulfate Content

Author(s): F. Goma

Publication: Special Publication

Volume: 132


Appears on pages(s): 403-418

Keywords: compressive strength; concretes; curing; fly ash; length changes; sulfates; tests; Materials Research

Date: 5/1/1992

The purpose of this research was to study the ability of Class C fly ash for high-volume concretes when its sulfate content reaches the limit in its specifications. The laboratory test items were compressive strength, length change in concrete cylinders 70 x 780 mm, and quantitative analysis of all materials. Calcium hydroxide content in concretes was also measured with a new method by selective extraction. This is suggested to determine the decreasing content of the calcium oxide in concretes, as responsible for he pozzolanic behavior or its carbonation degree. One type of Class C fly ash with different ages and three classes of cements with different C3A content were tested. The influence of curing conditions in tap water immersion, the different potential contents of ettringite, and calcium hydroxide were taken into account. The following results were obtained. The content of SO3 in fly ash very near the 5 percent specification limit used in high-volume concretes with substitutions of 60 percent of cement gave no undue expansions for given conditions. No significant length changes in concrete were observed in any of the tests. The strength development shows good values, especially when the concrete was cured in tap water.