Compositional Analysis of Beneficiated Fly Ashes.
Compositional Analysis of Beneficiated Fly Ashes.
(3762 K)
Stutzman, P. E.; Centeno, R. L.
NISITR 5598; 23 p. May 1995.
Available from:
National Technical Information Service
Keywords:
building technology; composition; concretes; fly ash;
mineralogy; mortar; particle size; reaction kinetics
Abstract:
Understanding the material properties of mineral
admixtures will help in providing a better understanding
of the factors that control their performance in
concrete. This study, a part of an effort by that
includes reaction kinetics, microstructure development,
and simulation modelling, examines the composition of
the crystalline components of beneficiated fly ashes of
different origin. Different sized fractions of fly
ashes produced by burning coal in different boilers were
examined by scanning electron microscopy and x-ray
powder diffraction. Each fly ash fraction was
predominantly glassy material with minor amounts of
quartz, mullite, anhydrite, magnetite, hematite, calcium
oxide, and possibly periclase. The glassy fraction
increased slightly with ash fineness and, for each size
fraction, was typical of silicious glasses found in
other fly ashes. Images of microstructures of mortars
incorporating 25%, by mass, fly ash replacement for
cement show increased packing density with the finer ash
fractions. The presence of unreacted fly ash and
calcium hydroxide in the mortars after 60 days of wet
curing indicates that the pozzolanic reaction is not
complete. The similarity of ash phase compositions
suggests that, at this age, strength gain may be
influenced more by the particle size than by
compositional differences among the ash fractions and
ashes produced under different firing temperature.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899