Specific surface,pozzolanic activity and composition of pulverized-fuel ash

This paper describes a laboratory investigation into the relations between the specific surface—as determined by different methods—the chemical composition, and the pozzolanic activity of pulverized-fuel ash (PFA). It is shown that the values obtained for specific surfaces of ashes vary according to the method of determination. However, it is likely that the highest value, the specific surface determined by nitrogen adsorption (N_dry), is the most appropriate value. Positive and negative correlations were found between N_dry specific surface and the carbon content of the ash, and between N_dry specific surface and total silica and alumina contents, respectively. Ashes with high N_dry specific surface values are characterized by angular porous particles, whereas those with low N_dry specific surface values appear to be primarily composed of non-porousspherical particles. A negative correlation was found between pozzolanic activity and N_dry specific surface. However, there was little correlation between pozzolanic activity and chemical composition. It is recommended that an upper acceptable limit should be placed on the N_dry specific surface of PFA when it is to be used for purposes requiring high pozzolanic activity.