Nanoindentation characteristics of alkali-activated aluminosilicate materials

Low calcium ground fly ash and metakaolin were activated with a sodium-silicate solution and cured under ambient and heat conditions. The resulting mature aluminosilicate composites were indented by several series of grids consisting of approximately 100 indents in each. The effective material volume affected by an indent was ≈1 μm3. Statistical histogram plots of elastic properties of the main reaction product (N-A-S-H gel) as well as of other material phases were constructed. The deconvolution of histograms via four Gaussian distributions testified that the mature N-A-S-H gel has almost the constant intrinsic Young’s modulus ≈17–18 GPa, irrespective of the curing procedure and activated material, i.e. fly ash or metakaolin.