The use of fly ash as a supplementary cementitious material (SCM) has increased in the
last century due to its various environmental benefits as a recycled product. Within the
last 60 years, it has been found that it can be used to effectively control damage
induced by Alkali-Silica Reaction. However, it is not completely understood how to
properly assign a dosage of fly ash to control the reaction. This depends greatly on the
fly ash characteristics (e.g. composition, particle size, and reactivity), the reactivity of
the aggregate (e.g. high to low reactivity level) and the environmental exposure
conditions. The characteristics of the fly ash depend on the coal source being burned
and the burning conditions that result in the fly ash formation. A major concern when
supplementing cement with fly ash for ASR mitigation is the effect of the alkali
contribution of the fly ash to the concrete pore solution. Current test methods cannot
accurately determine the alkali contribution of fly ashes and there is no standardized
test method to doing so.
When contributed by the implementation of a SCM, alumina has been found to play a
role in the ability of an SCM to mitigate ASR-induced damage. It has been observed that
fly ashes containing higher levels of alumina (18-25%) tend to improve concrete
durabilty more effectively when compared to fly ashes with lower levels of alumina.
Additionally, the use of metakaolin, which is composed of 45-50% alumina, has been
found to lessen expansion with a lower percentage of cement replacement than would
be required if fly ash is used. Furthermore, the use of fly ash with another SCM
material, a high quality ultra-fine fly ash or alumino-siliceous metakaolin, in ternary
blends may improve the performance of fly ash resulting in a broadening of the
spectrum of SCMs usable for ASR mitigation.
For successful use of SCMs, it is important to develop an understanding of the alkalisilica
reaction and the ability of such SCMs to control expansion. This report provides an
overview of alkali-silica reaction and the use of fly ash and metakaolin as SCMs to
mitigate expansion due to the reaction, with an emphasis on the role of alumina when
contributed from the two materials. / Graduation date: 2012
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28787 |
| Date | 13 March 2012 |
| Creators | Warner, Skyler J. |
| Contributors | Ideker, Jason |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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