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Mechanical Properties and Durability of Concrete Made with High Volume Fly Ash Blended Cements

This paper describes the development of high-volume fly ash (HVFA) blended cements. The blended cements were made by combined grinding 45% of ASTM Type III cement clinker, 55% of ASTM class F fly ash, a small percentage of gypsum, and 0.7% of superplasticizer by weight of the cement including clinker, fly ash, and gypsum. Several concrete mixtures were made with the control and the blended cements; also, concrete mixtures were made in which high volumes of fly ash had been added at the concrete mixer. A large number of test specimens were cast for determining the mechanical properties and durability characteristics of the hardened concrete. The results of the investigations indicated that the mechanical properties of concrete made with the HVFA blended cement are superior to that made with laboratory-produced portland cement and where the fly ash had been added as a separately batched material at the mixer. The durability characteristics of these two concretes are comparable except that the de-icing salt-scaling resistance of concrete made with the HVFA blended cement is considerably inferior to that of the concrete in which fly ash had been added as a separately-batched material at the mixer. The coarse Genesee fly ash that fails to meet the fineness requirements of ASTM C 618 has been used successfully to produce a HVFA blended cement. The mechanical and durability properties of concrete made with this blended cement (BCGS), are comparable to the concrete made with the HVFA blended cement produced with the finer Sundance fly ash. Thus, the production of HVFA blended cements offers a possible way for the utilization of coarse fly ashes. The intergrinding of the dry superplasticizer with clinker, fly ash and gypsum to produce HVFA blended cements did not pose any problems; however, for equal performance as regards to slumps, the amount of the superplasticizer needed in the blended cements was higher compared to that needed when superplasticizer was added separately at the mixer.