Use of conditioned PFA as a fine aggregate component in concrete

This paper describes a study carried out to examine the use of conditioned, or moistened, pulverized-fuel ash (CPFA) as a component of fine aggregate ill concrete, i.e. as a nearly inert Type 1 addition, as described in BS 3892: Part 2. A fine and coarse PFA were used, after storage at a moisture level of 10% for 1 and 12 months, to determine the influence of CPFA/sand combinations (with ratios up to 0.15) on concrete fresh properties and strength development. III addition, the activity of CPFA was examined using calorimetry and thermogravimetric analyses on mortar specimens. Inclusion of CPFA as a fine aggregate component in concrete led to reductions in workability and bleeding, particularly with longer-term stored material, but handling: characteristics were otherwise unaffected. It was possible to overcome the workability loss, maintain low level bleeding and enhance the other fresh properties, through the use of a super-plasticizing admixture at reasonable dosage. For hardened concrete, all mixes containing CPEA/sand exhibited improved strength development, compared to reference sand mises, with greatest benefits obtained with short-term stored material. These effects were compared by the hydration studies which indicated increased heat of hydration and lime consumption with CPFA. The practical implications of the study are also examined.