Mechanical treatment of fly ashes .2. Particle morphologies in ground fly ashes (GFA) and workability of GFA-cement mortars

Mechanical treatment (by grinding) effects on particle morphology and specific gravity of fly ashes, and workability of ground fly ash (GFA) cement mortars have been studied. Different shape morphologies of GFA particles have been established: shell shaped and irregular solid fragments. Real and bulk specific gravity values were measured, proving that grinding process increased the content of poor shape particles. Particle Packing Factor (PPF) for GFA decreased below 50%. Workability of GFA-cement mortars is negatively affected, but it is still greater that only cement mortar one. Good correlations between flow table spread (FTS) values per water volume unit and fly ash replacing percentage have been obtained, and a relative workability factor W-r is established. Determination of W-r value permits to compare the effect of grinding or other fly ash processing methods on workability of mortars. Finally, good linear relationships between W-r values and the inverse of mean diameter particle or calculated specific surface area were found.