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Reaction Products in Fly Ash Concrete

Published online by Cambridge University Press:  25 February 2011

Mark D. Baker  and
Joakim G. Laguros
Mark D. Baker
Affiliation:
The Dolese Company, Oklahoma City, Oklahoma
Joakim G. Laguros
Affiliation:
The University of Oklahoma, Norman, Oklahoma
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Abstract

The setting and strength gaining process of PC concrete containing Class C high lime fly ash were related to the reaction products identified using XRD and SEM. Four fly ash concrete mixes (20, 30, 40, and 50 percent replacement of cement by fly ash) and similar paste mixes were compared to control mixes for curing periods up to one year. Setting time and early compressive strength were adversely affected by the addition of fly ash. Beyond one week all of the fly ash concrete mixes gained strength at a faster rate than the corresponding control mixes. XRD studies suggest that the retardation mechanism may be associated with the high levels of ettringite formed early in the hydration process and its conversion to monosulfoaluminate. A decrease in the level of calcium hydroxide, typical of pozzolanic activity, was not in evidence. SEM micrographs of fly ash spheres in concrete at the various stages of hydration reveal an intricate crystal framework. A simple heat of hydration test is presented which helps explain the strength gains observed.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 43: Symposium M – Fly Ash and Coal Conversion By-Products I , 1984 , 73
Copyright
Copyright © Materials Research Society 1985

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References

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