Use of low grade kaolinitic clays in development of a pozzolan-cement binder system

The use of calcined, kaolinite-rich clays as pozzolanic components in blended cements has gained a great deal of attention in recent years. This reflects its impact on reducing the total embedded carbon dioxide associated with concrete made from such binders. Reduction of CO2 is two-fold: the clays are calcined at a lower temperature than Portland cement and also replace some of the clinker in the binder phase. Pure kaolinite clay is relatively expensive however, as it is used in other industrial applications.
This work studies the potential utilization of low-grade (less pure) kaolinitic clay as a supplementary cementitious material in mortar formulations. Examination by XRD revealed the presence of kaolinite, illite and quartz as the main clay minerals present in the materials. The clay samples were dried and calcined at 600 oC and the effect of heat treatment on the physical, mineralogical and microstructural properties studied.
The calcined clay was uniformly blended with ordinary Portland cement at replacement levels of 10%, 20% and 30% by weight and their mechanical properties determined after 7 and 28 days. Blended cements containing 10 wt.% and 20 wt.% calcined clay were seen to have compressive strength results comparable to the reference cement at 28 days.