Influencing factors on micromechanical properties of calcium (alumino) silicate hydrate C-(A-)S-H under nanoindentation experiment

In Portland cement-based concrete, calcium (alumino) silicate hydrate (C-(A-)S-H) is the principal binding phase that governs its physical, mechanical, and durability properties. In this study, micromechanical properties of compacts made of synthetic C-(A-)S-H powder were investigated with nanoindentation, and various influencing factors were identified. It was revealed that a normal distribution and convergence of test data could be attained with an indentation depth > 350 nm. Higher conditioning relative humidity, pressure, and holding time aided consolidation of the powder and led to an improved elastic modulus. No remarkable influence of strain rate (0.025-0.1 s(-1)) and vibration frequency was noted. While the Al-incorporated CASH exhibited superior mechanical properties relative to C-S-H, all the C-(A-)S-H compacts yielded lower elastic modulus values as compared to data from fully hydrated C3S paste, mainly attributable the phase bonding, packing density, chemical composition, and the presence of phases other than C-(A-)S-H in the C3S sample.