Effects of Ground and Classified Fly Ash on Properties of High-Performance Concrete

The investigation presented in this study shows an example of the improvements of fly ash fineness achieved by a physical process, air-classification and a mechanical process, grinding. To make high-performance concrete, three different types of fly ash namely, original, air-classified, and ground fly ash, with different finenesses was used as cement replacement. The percentage replacement of cement by each type of fly ash was used as 0, 10, 15 and 20% by weight of cementing materials. Finally, the results were compared with silica fume concrete. The results showed that substitution of part of the cement with original or classified fly ash produces concrete mixtures with greater workability than the control as measured by slump and slump-flow. On the contrary, it was found that the ground fly ash, having more or less the same degree of fineness as classified fly ash resulted in a lower workability due to the loss of its spherical shape and lubricant effect. The inclusion of original fly ash reduced the early strength and this reduction was more significant with the increase of percentage replacements. Classified and ground fly ash improved the early strength. The long-term strength development of classified and ground fly ash concrete was found to be considerably higher than that of control concrete for all the percentage replacements.