On the glass present in low-calcium and in high-calcium flyashes

Abstract

A suite of 16 American flyashes ranging in analytical CaO content from less than 2% to approximately 27% was subjected to x-ray diffraction and the position of the glass diffraction maximum determined. Flyashes of analytical CaO content of up to about 20% showed maxima indicative of siliceous glass. Within this range the 20 angular position of the maximum was found to increase linearly with CaO content, suggesting progressive modification of the siliceous glass structure with increasing calcium content. Flyashes of analytical CaO content higher than about 20% showed a glass diffraction maximum at a constant and much higher 20 angle, indicative of calcium aluminate glass structural type. The latter glass may be significantly more reactive in concrete.