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Concretes containing mixed recycled aggregate (RA) have a larger number of coarse aggregate/paste interfacial transition zones (ITZs) than conventional concretes, due to the various component materials present in recycled aggregate. This study investigated the properties of various RA/paste ITZs in concrete using nanoindentation and scanning electron microscopy (SEM) and analysed the possible impact of the properties of the ITZs on the macromechanical performance of recycled concrete. It was found that the elastic modulus of the ITZ varies with the type of constituent materials present in recycled aggregate, with ITZs associated with organic components (e.g. wood, plastic and asphalt) exhibiting lower minimum elastic modulus values. The impact of ITZ properties on macro-mechanical properties of concrete depends on the relative content of different constituent materials present in the recycled aggregate and the micro-mechanical properties of the ITZs involved.

The influence of the local micro-properties of the interfacial transition zone (ITZ) on macro-properties on the behaviour concretes is studied for recycled concretes made with 20% and 25% recycled ceramic aggregate from sanitary ware waste. This study carried out using nanoindentation and SEM technique aims to explore interface thickness and variations in its elastic modulus. The results show that the minimum and mean values of the elastic modulus and the ITZ thickness impact concrete mechanical and elastic properties to different degrees. Finally, that nanoindentation provides an indispensable tool for studying and assessing the effect of new materials (e.g. recycled aggregates) on the micromechanical properties of the interfacial transition zone (ITZ) and its effect on engineering properties (compressive and splitting tensile strength and modulus of elasticity) of these new concretes.

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