Assessment of pozzolanic activity of calcined coal-series kaolin

Coal-series kaolin (from the Yichang region of China) was tested as a potential pozzolanic material to be used in the cement and concrete industry. Thermal treatment was used to activate the raw coal-series kaolin (RCK). Phase identification before and after calcination was studied by X-ray diffraction and Fourier transform infrared spectroscopy. The pozzolanic activity of calcined coal-series kaolin (CCK) was tested by two direct methods, modified Chapelle and Frattini tests, and one indirect method, strength activity index. Aside from thermal treatment, grinding process for CCK was also used to evaluate the effect of particle size distribution on pozzolanic activity. The results showed that pozzolanic activity of CCK was greatly influenced by dehydroxylation and particle size. The modified Chapelle test overestimated pozzolanic activity in the low pozzolanic region (0-1300 mg CH/g CCK), and was suitable for complete dehydroxylation samples. The Frattini test accurately assessed CH consumption by pozzolanic reaction, and the strength activity index confirmed the physical effect contribution to CS enhancement at earlier stage and pozzolanic reaction contribution to enhanced microstructure (pore and grain size refinement) and hence improved mechanical strength of cementitious material at later stage.