PFA fineness and its use in concrete

Abstract

The object of the investigation was to determine a satisfactory method of assessing the Jineness of pulverized fly-ash (PFA) which provided a reasonable correlation with the workability of concretes with similar compositions except for the type of fly-ash used. Neither the standard air permeability tests nor the residue on a 45 μm sieve were found to provide a good indication of the complete size distribution of a fly-ash. The air permeability provides a value which does not necessarily vary with the specific surface, and the 45 μm sieve merely considers the division at one size only. However, if an accurate assessment of the size distribution is expressed in terms of a simple parameter such as the grading modulus, the latter then shows very good correlation with the workability of the resultant PFA concretes, as indicated by the VB time. A useful indication of the potential strength of the PFA concrete could also be given by the grading modulus.