Role of High-Volume Fly Ash Concrete in Controlling Alkali-Aggregate Activity


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Title: Role of High-Volume Fly Ash Concrete in Controlling Alkali-Aggregate Activity

Author(s): Suresh Ramachandran, V. Ramakrishnan, and Dan Johnston

Publication: Special Publication

Volume: 132


Appears on pages(s): 591-614

Keywords: accelerated tests; alkali-aggregate reactions; chemical tests; cement-aggregate reactions; expansion; fly ash; mortars (material); portland cements; sands; Materials Research

Date: 5/1/1992

The use of high-volume fly ash as a supplementary cementing material in controlling alkali-aggregate reactivity is an attractive solution. Fly ashes are often used in reducing the expansions due to alkali-aggregate reaction in concrete. However, in the past, only smaller quantities of fly ash, less than 30 percent by weight of cement, have been used. This paper presents the results of a study to determine the influence of very high quantities of fly ash in reducing the expansion due to alkali-aggregate reactions. Ten samples of sands collected from various locations in South Dakota were tested for alkali-aggregate reactivity using both standard ASTM C 227 and accelerated test methods. Five of the sands that caused greater expansions than permitted were tested with high fly ash contents, using the accelerated test method. Cements satisfying ASTM Type I and a low-calcium fly ash (ASTM Class F) were used for the entire investigation. The water/fly ash + cement ratio was 0.44 and the fly ash/fly ash + cement ratios expressed as percentages were 40, 50, 60, and 70. Control mortar specimens containing the same Type I cement and alkali content were used for comparison. An accelerated test method proposed by the Canadian Standards Association was used for the detection of potentially deleterious expansion of mortar bars. The test results had shown that high fly ash replacement levels were very effective in reducing the expansion due to alkali-aggregate reaction. The expansions of the mortar bars made with the highly reactive sands and high volumes of fly ash were negligible as measured in the accelerated test method.