Microstructure, hydration and nanomechanical properties of concrete containing metakaolin

• Microstructure and nanomechanical properties of concrete containing metakaolin.
• Metakaolin transforms portlandite into C–S–H gel by means of pozzolanic reaction.
• Addition of metakaolin reduces porosity and creates nucleation sites for hydration.
• Metakaolin modifies the relative proportions various phases of C–S–H gel.

This paper presents the results of an experimental investigation carried out to evaluate the microstructure, hydration and nanomechanical properties of concrete containing metakaolin. The properties of concrete containing metakaolin at 0%, 5%, 10% and 15% by mass of cement were studied for their compressive strength, sorptivity and carbonation resistance at two different water–binder ratios. It was found that 10% of the Portland cement could be beneficially replaced with the metakaolin to improve the sorptivity and carbonation resistance of concrete. In order to have a better understanding of the microstructure, hydration and nanomechanical properties various analytical techniques such as XRD, MIP and nanoindentation studies were carried on cement paste samples (with and without 10% MK). Test results showed that the incorporation of metakaolin modifies the cement paste in four different ways. Firstly, by transforming portlandite into C–S–H gel by means of pozzolanic reaction, secondly by reducing the porosity, thirdly by creating nucleation sites for hydration and finally, by modifying the relative proportions various phases of C–S–H gel.