Title:
Effects of Alkalies in Class C Fly Ash on Alkali-Aggregate Reaction
Author(s):
C. Lee
Publication:
Symposium Paper
Volume:
114
Issue:
Appears on pages(s):
417-430
Keywords:
alkali-aggregate reactions; alkali content; alkalies;
Cements; expansion: fly ash; mineral admixtures; mortars
(material); silica gel
DOI:
10.14359/10016
Date:
5/1/1989
Abstract:
Effects of alkalies in Class C fly ash on Alkali-aggregate reaction were studied by using two cements, a type I high-alkali cement and a type II low-Alkali cement, and three Class C fly ashes. Mortar bar expansion was measured according to ASTM C 441. Reaction products of alkali-aggregate reaction were examined n by XRD, SEM, and EDAX. were to study: The purposes of this research (1) the significance of the standard mortar bar test in determining the degree to which high and low-alkali cement could be replaced by Class C fly ashes, and (2) effect of fly ash alkali contents on alkali reactivity. Expansion of mortar bars prepared using high-alkali cement increased at low replacement levels but decreased at high replacement levels for curing periods up to 12 weeks at 38 C; whereas expansion of mortars prepared using low-alkali cement increased at all Levels of fly ash replacements up to 40% by volume. A critical equivalent Na20/Si02 mole ratio was identified and found to characterize alkali reactivity. No crys-talline reaction products could be identified by XRD. Results of SEM and EDAX showed that the reaction product was an alkali-silicate gel, composed mainly of silica, sodium, potassium, and calcium, with their relative amounts varying within the gel.