Prasanth Tanikella and Jan Olek, Purdue University
Indiana Department of Transportation through the Joint Transportation Research Program
amount of calcium hydroxide forme, Fly ash, heat of hydration, Paste system, set time, strength activity index, the non-evaporable water content
This research was an attempt to quantify the effects of fly ashes on the properties of pastes as a function of (a) the mean particle size of the fly ash particles, (b) their fineness, and (c) their chemical composition. In addition, since the type and the amount of glass present in the fly ash significantly affect its reactivity, this property was also included in the investigation. Twenty different fly ashes (both, ASTM Class C and Class F), obtained from power plants in and around Indiana, were characterized during Phase 1 of the study.The information collected included physical characteristics, chemical composition, and the amount and type of glass present. Phase 2 of the study consisted of evaluation of various properties of binary paste systems (portland cement with 20% of cement of fly replacement). The evaluated properties included the set time, the heat of hydration, the strength activity index, the non-evaporable water content, and the amount of calcium hydroxide formed at different ages. These results obtained from both phases of the study were used to build statistical models for prediction of previously evaluated properties for any hypothetical fly ash with similar characteristics. The models included only the most significant variables, i.e., those which were found to most strongly affect any specific property. The variables to be included in the model were selected based on the adjusted R2 values. As a result of the modeling process, it was found that the sets of statistically significant variables affecting the properties consisted of both physical and chemical characteristics of the fly ash and that the combination of these variables was unique for each property evaluated.