Kaolinitic calcined clays – Portland cement system: Hydration and properties

• Kaolinitic calcined clays are an effective pozzolan when they are appropriately calcined and ground.
• The reactivity of kaolinitic calcined clays depends on the structure of kaolinite in raw clay.
• The rate of pozzolanic reaction of kaolinitic calcined clays modifies the mechanical properties of the blended cement.
• After calcination and grinding, raw clay containing disordered structure has very high pozzolanic activity.
• Kaolinitic calcined clays produce a high reduction of the water sorptivity coefficient.

This paper examines the influence of type of kaolinite in the raw clay on the performance of calcined clays as supplementary cementing materials. Two kaolinitic clays were characterized, calcined then ground and used as partial replacement of Portland cement at 15% and 30% by mass. The results show that both kaolinitic calcined clays are an effective pozzolan with different reaction rate. The reactivity is related to the specific surface area obtained after calcination and it depends on the structure of kaolinite. Raw clay containing disordered structure presents a very high pozzolanic activity allowing high replacement levels (30%) in blended cements.