Optimizing the thermal treatment of Abeokuta kaolin (south-west Nigeria) for production of natural pozzolan

The use of pozzolans in construction works have been on the rise in recent times, an effort driven by the need for environmentally friendly alternatives to cement. Calcined kaolin is a natural pozzolan currently being researched and optimum pozzolanic performance has been related to its production parameters. This work investigated the optimum calcining temperature and time for a kaolin source located in Ajebo, south-west Nigeria, using the degree of de-hydroxylation (Dtg) as a measuring parameter. Preliminary DTA revealed that the formation phase was between 500°C and 750°C. Using this result as a reference, the kaolin samples, each 300 gm, were thereafter calcined at temperatures of 550°C, 600°C, 650°C, 700°C, 750°C and 800°C, respectively, each for 1 hr and 2 hrs in an electric muffle furnace. At each instance, Dtg was obtained as the mass loss calculated as a percentage of the original mass. The process was repeated two more times and averages were calculated. Results showed that Dtg peaked at the 750°C-1 hr combination (0.95), whereas marginal differences were recorded at some lower temperatures (0.91 for 650°C-2 hrs; 0.91 for 700°C-1 hr; 0.93 for 700°C-2 hrs). The paper concludes by advising on these temperature-time combinations for optimum calcining of Ajebo kaolin.