INFLUENCE OF DIFFERENT-SIZED FRACTIONS OF A FLY-ASH ON WORKABILITY OFMORTARS

The study of fly ash as a replacement to mortar workability using a fl ow table is presented. Flow table spread (FTS) values were measured an d correlations among fly ash replacing percentages, water volumes and granulometric distributions of fly ashes have been established. Linear relationships between FTS values and water volumes were obtained in t he 200-225 mL water range (0.5 water/cement + fly ash ratio, 3.0 natur al sand/cement + fly ash ratio). An increase of water volume implies g reater FTS values. Original fly ash was separated in four fractions wi th different granulometric distributions. FTS values increase as do sp ecific surface, and FTS values decrease as mean diameter of fly ash in crease. For the finest fraction, the lubricant effect was counteracted by water adsorption on fly ash particles surfaces. The shape distribu tion curves of fly ashes (original and their fractions) has an importa nt influence on workability.