Influence of different calcined clays on the water transport performance of concretes

This study compares the pozzolanic activity of kaolinitic and illite clays after calcination as they are the most abundant types of clays worldwide. The impact of calcined clays on microstructure development was tested by determining the porosity of cement paste as well as by phase and optical analysis of the cement matrix and the interfacial transition zone of concrete. As water transportation with damaging carbonate or chloride ions is the main reason for reduced durability of reinforced concrete, the results were complemented with water absorption tests on blended concretes. At 28 days, the system with calcined kaolinitic clay revealed a higher densification of its microstructure with a lower water absorption rate compared with plain concrete and concrete with calcined illite clay, which is related to its higher pozzolanic reactivity. Nonetheless, calcined illite clays can be considered as a low-cost clinker replacement as a significant pozzolanic contribution is detectable and after 90 days, the water absorption behaviour is comparable to those of the other systems investigated.