In the past, different investigations have focused on waste containing kaolinite as an alternative source for recycled metakaolinite. However, it is well known that the activation conditions play an important role in the characteristics of the final product. This research presents an exhaustive study about the evolution of the mineralogical phases during the pozzolanic reaction of two metakaolinite by-products obtained from different activation processes: activation of paper sludge at lab scale (700ºC and 2 hrs) and at industrial scale (720-740ºC and 20-30 minutes) with a fluidized bed combustion system. It is shown that both metakaolinite by-products exhibit a different pozzolanic behaviour, suggesting a direct influence on the subsequent performance of new blended cement matrices. The metakaolinite by-product obtained at lab-scale (MWL), generates hydrotalcite type structures as predominant crystalline phase in the pozzolan/Ca(OH)2 system up to 28 days of reaction. Stratlingite (C2ASH8) also appeared as minor stable phase after 7 days of reaction. On the other hand, the metakaolinite by-product from industrial process (MWI) favours the formation of C4A H12 phase, whereas stratlingite was not identified.

MAT2009-10874-CO3-01/02/03

Peer reviewed