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Evaluating the Hydration of High Volume Fly Ash Mixtures Using Chemically Inert Fillers



Igor de la Varga, Javier Castro, Dale P. Bentz, Franco Zunino, Jason Weiss


Fly ash is frequently used as a replacement for cement in concrete. However, questions remain regarding the influence that fly ash has on the hydration of cement. This paper examines physical aspects (e.g., surface nucleation, cement particles spacing) and chemical aspects (e.g., pozzolanic and hydraulic reactions) of the fly ash and cement in mixtures containing high volumes of fly ash. In addition to using fly ash, a chemically inert filler was used consisting of a blend of fine silica sands with approximately the same particle size distribution as that of the fly ash. The paper compares reactivity results from 1) cement, 2) cement-fly ash and 3) cement-inert filler systems. Isothermal calorimetry, internal relative humidity and electrical conductivity measurements are used to better evaluate the role played by the fly ash in these systems at later ages. The internal relative humidity assesses self- desiccation in a sealed system, which is an indication of the ongoing chemical reaction, while the electrical measurements assess transport properties and the type of microstructure that forms. These parameters can be used to evaluate the extent of reaction at later ages. The results provide a decoupling of the physical and chemical effects of high volume fly ash on cement hydration at early and later ages.
Construction and Building Materials


Filer effect, high volume fly ash, hydration, internal relative humidity, isothermal calorimetry.


de la Varga, I. , Castro, J. , Bentz, D. , Zunino, F. and Weiss, J. (2017), Evaluating the Hydration of High Volume Fly Ash Mixtures Using Chemically Inert Fillers, Construction and Building Materials, [online],, (Accessed April 15, 2024)
Created December 5, 2017, Updated October 12, 2021