Evaluation of reclaimed and remediated fly ashes as a substitute for class F fly ash in concrete

With the availability of Class F fly ash decreasing due to competing fuel sources and emission standards, suppliers are forced to find alternative methods to meet the demand for it, such as, reclaiming ponded or landfilled ashes or remediating ashes that do not meet ASTM International specifications. These processes result in a fly ash that varies in physical and chemical composition from “production” Class F fly ash. This research studied five of these alternative materials, which included: two reclaimed fly ashes and three remediated fly ashes. For these materials to qualify as acceptable substitutes for production Class F fly ash, they must pass ASTM requirements, as well as have comparable performance in paste, mortar and concrete testing. In order to correlate performance with material properties, the physical and chemical characteristics of the reclaimed and remediated fly ashes were measured using standardized ASTM tests as well as advanced characterization tests. The performance of the reclaimed and remediated fly ashes were evaluated through paste, mortar and concrete workability; pozzolanic activity using a new isothermal calorimetry-based test, portlandite consumption through differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), and mortar and concrete compressive strength tests; and their ability to suppress deleterious expansion due to sulfate attack or alkali-silica reaction (ASR). To evaluate the potential of these alternative ashes for field use, they were compared to a portland cement control, production fly ash and an inert quartz filler. Results showed that all the reclaimed and remediated fly ashes exhibited pozzolanic behavior in the testing presented in this thesis and are able to perform similarly to a production Class F fly ash in certain applications and environments. All materials were able to suppress deleterious expansion due to ASR, however, the remediated fly ashes performed well in sulfate resistance and compressive strength testing, while the reclaimed fly ashes excelled in flowability with one of the reclaimed fly ashes also excelling in compressive strength.