Micromechanical analysis of interfacial transition zone in alkali-activated fly ash-slag concrete

This paper systematically investigates the micromechanical properties of interfacial transition zone (ITZ) in alkali-activated fly ash-slag (AAFS) concrete using nanoindentation, backscattered electron microscopy and energy dispersive spectroscopy. Results indicate that the micromechanical properties of ITZ depend on the chemical composition of reaction products and its microstructural characteristics. The ITZ with high proportion of N-C-A-S-H and C-A-S-H gels tends to have high elastic modulus because of their superior micromechanical properties. The formation of reaction products would refine the microstructure of ITZ and improve its elastic modulus. The evolution of micromechanical properties of ITZ can be divided into three stages: (i) accelerated growth stage via fast chemical reactions (<12 h); (ii) stationary stage via stable chemical reactions (12 h-7 d); (iii) decrement stage via microcrack propagation (7 d-28 d). ITZ is not the weakest region in AAFS concrete due to its desired micromechanical properties and compact microstructure compared to paste matrix.

Automated summary

This study systematically investigates the micromechanical properties of the interfacial transition zone (ITZ) in alkali-activated fly ash-slag (AAFS) concrete, revealing that the properties depend on the chemical composition of reaction products and microstructural characteristics, with the evolution divided into three stages.