Evolution of mineralogical phases produced during the pozzolanic reaction of different metakaolinite by-products: Influence of the activation process

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 (700 °C and 2 h) and at industrial scale (720–740 °C and 20–30 min) with a fluidized bed combustion system.It is shown that both metakaolinite by-products exhibit a different pozzolanic behavior, suggesting a direct influence on the subsequent performance of new blended cement matrices. The metakaolinite by-product obtained at lab-scale (MWL), generates an additional phase (carbonate/metakaolinite 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) favors the formation of C4AC¯H12 phase, whereas stratlingite was not identified.

► Different mineralogy in function of MK waste source.
► Influence of activation conditions on the pozzolanic reaction.
► Pozzolan from laboratory favors the formation the hydrotalcite type structures.
► Pozzolan from industrial process, the monocarboaluminate hydrate is predominant.