Nano/micromechanical characterisation and image analysis on the properties and heterogeneity of ITZs in geopolymer concrete

Heterogeneity of interfacial transition zones (ITZs) is a key factor for the properties and failure mechanism of geopolymer concrete. The nano/microscale properties and heterogeneity of the ITZs (the top, bottom and lateral interfaces) prepared by encompassing polished aggregates in the modelled fly ash-based geopolymer concrete were statistically investigated in this study. The nanoindentation and nanoscratch results show that the nano/micromechanical properties of the gel-related phases of ITZs at the top and bottom boundaries are higher than the corresponding ones at the lateral boundaries and bulk paste. The mechanism of the better properties of ITZs at the top and bottom boundaries is unveiled based on quantitative image analysis of the amount, diameter and proportion distribution of fly ash particles. A strategy of controlling heterogeneity of ITZs and using polished aggregates, rapid scratch and statistical analysis is proposed to investigate more complicated ITZs within acceptable testing duration. • The increase of fly ash diameter with distance from aggregate is caused by the large particles • The top and bottom sides from aggregate present more fly ash particles than the lateral side region • The top and bottom ITZs have higher modulus and hardness than the lateral side ones and bulk paste • The bleeding in geopolymer concrete is severer than that in Portland cement concrete