TITLE:
Calcined Clay Pozzolan as an Admixture to Mitigate the Alkali-Silica Reaction in Concrete
AUTHORS:
James Sarfo-Ansah, Eugene Atiemo, Kwabena Appiah Boakye, Delali Adjei, Albert A. Adjaottor
KEYWORDS:
Calcined Clay Pozzolan, Alkali-Silica Reaction, Expansion, Sodium Silicate gel, Calcium Silicates
JOURNAL NAME:
Journal of Materials Science and Chemical Engineering,
Vol.2 No.5,
May
21,
2014
ABSTRACT: Calcined clay pozzolan has been used to replace varying portions of high
alkali Portland limestone cement in order to study its effect on the
alkali-silica reaction (ASR). Portland limestone cement used for the study had
a total Na2Oeq of 4.32. Mortar-bar expansion decreased as
pozzolan content in the cement increased. The highest expansion was recorded
for reference bars with no pozzolan, reaching a maximum of 0.35% at 42 days
whilst the expansion was reduced by between 42.5% and 107.8% at 14 days and
between 9.4% and 16.4% at 84 days with increasing calcined clay pozzolan
content. Mortar bars with 25% pozzolan were the least expansive recording
expansion less than 0.1% at all test ages. X-ray diffractometry of the hydrated
blended cement paste powders showed the formation of stable calcium silicates
in increasing quantities whilst the presence of expansive alkali-silica gel,
responsible for ASR expansion, decreased as pozzolan content increased. The
study confirms that calcined clay pozzolan has an influence on ASR in mortar
bars and causes a significant reduction in expansion at a replacement level of
25%.