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.
and Centeno, R.
Compositional Analysis of Beneficiated Fly Ashes., NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.6028/NIST.IR.5598
(Accessed February 21, 2024)