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An Improved Basis for Characterizing the Suitability of Fly Ash as a Cement Replacement Agent



Tandre Oey, Jason Timmons, Paul E. Stutzman, Jeffrey W. Bullard, Magdalena Balonis, Mathieu Bauchy, Gaurav Sant


Fly ash is a critical yet underutilized material for partial replacement for ordinary portland cement (OPC) in the binder fraction of a concrete. Significant compositional variability, and a lack of rigorous classification methods currently limit fly ash use. For example, the performance of OPC-fly ash blends cannot be estimated a priori using current characterization standards (e.g., ASTM C618). In this study, fly ashes spanning a wide compositional range are characterized in terms of glassy and crystalline phases using a combination of X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM-EDS) techniques. The compositional data are distilled to a parameter - the network ratio (Nr, unitless) - which represents the network behavior of atoms that form alkali/alkaline earth-aluminosilicate glasses that make up fly ashes. Nr is correlated to known composition-dependent features including the glass transition temperature and amorphous XRD peak ("hump") position. Analysis of heat release data and compressive strengths are used to evaluate the impact of fly ash compositions on reaction kinetics, and on the engineering properties of cement-fly ash blends. It is shown that fly ashes hosting glasses with a high network ratio, i.e., having a less stable glass structure, are more reactive than others.
Journal of the American Ceramic Society


fly ash, glass, reactivity, strength gain, setting, composition


Oey, T. , Timmons, J. , Stutzman, P. , Bullard, J. , Balonis, M. , Bauchy, M. and Sant, G. (2017), An Improved Basis for Characterizing the Suitability of Fly Ash as a Cement Replacement Agent, Journal of the American Ceramic Society, [online], (Accessed April 24, 2024)
Created June 6, 2017, Updated October 12, 2021