Nanomechanical Properties of Interfacial Transition Zone in Concrete

Abstract

This research provides better understanding of the nanostructure and the nanoscale local mechanical properties of the interfacial transition zone (ITZ) in concrete. Nanoindentation with in-situ scanning probe microscopy imaging was used to compare the properties of the bulk paste with the properties of the ITZ between paste and two different types of aggregates. ITZ was found to be extremely heterogeneous with some areas as strong as the bulk matrix. Higher concentration of large voids and cracks along the interface was observed due to poor bonding. Nanoindentation results on relatively intact areas of the interface disagreed with the notion of increasing elastic modulus with distance from the interface. Depending on the aggregate type, average modulus of the ITZ was 70% to 85% of the average modulus of the paste matrix. The main problem the ITZ poses on the overall mechanical properties of concrete was concluded to be due to extreme heterogeneity within the interface and poor bonding between aggregate and paste. It was noted that the connectivity of the weaker areas such as large voids and cracks along the interface governs failure.