Nano-macro correlation of nano-silica concrete

Abstract

Concrete mixes using progressively finer size nano-silica particles (7-150 nm) were prepared to study the effect of nano-size pozzolans (nano-silica). Conventional compression tests demonstrated progressively higher strength with finer size of the nano-silica down to 12 nm particle size. High-vacuum Scanning Electron Microscope tests revealed that the nano-silica provide nucleation sites for crystal growth thereby changing the structure of the material at the micron to sub-micron level. This paper will describe nano-indentation tests that were subsequently performed on the material. Nano-indentation data was evaluated to determine stiffness, hardness and elastic-plastic work with progressively increasing indentation depth for each material. Results show variability of nano-scale testing in concrete due to inherent lack of homogeneity and also demonstrate that nano-scale tests correlate with the macro-scale mechanical response giving credibility to the hypothesis that alteration of crystal micro-structure (as opposed to void ratio) with nano-silica affects mechanical response at the micro-scale, which translates to improved macro-scale properties. © The Society for Experimental Mechanics, Inc. 2013.