Influence of the calcination temperature on the properties of a mica mineral as a suitability study for the use as SCM

摘要

Calcined clays as SCM have the potential of compensating the future decrease of slag and fly ash. The present work dealt with a mica mineral, a common component of raw clays, and its change of properties during calcination. Raw and at four temperature levels calcined mica were investigated on the following properties: Water absorption capacity, specific surface area, particle size distribution, lattice parameters by XRD, heat flow and Al-/Si solubility. The results showed a low ion solubility throughout all samples. Thus, the contribution to the chemical pozzolanic reaction due to calcination was low. However, mica's physical and hygroscopic properties influenced the cement hydration. Contrary to common knowledge, which predicts a decrease in water absorption capacity with a decrease in BET specific surface area, calcined mica behaved in the opposite direction. To conclude, for mica containing raw clays the calcination temperature should be lower in regard to mica's physical hygroscopic properties, but higher in regard to pozzolanic reactivity of other phyllosilicates. Therefore, a balanced calcination temperature should be applied. These results can be used to assess their suitability as SCM in mortar and concrete.