Abstract
Tobermorite is a natural mineral found in the microstructure of special concretes, such as autoclaved concrete and oil well cement, and along with jennite has been extensively studied for their analogy to the layered atomic structure of calcium silicate hydrate (C-S-H), which is the main product of the hydration of Portland cement. By means of creep microindentation, this work aims at further investigating the viscoelastic behavior of such C–S–H minerals at various levels of relative humidity (RH) and porosity.First, samples of 1.4 nm tobermorite and jennite were synthesized at different porosities. Then, the probed material volume was brought to the hygral equilibrium at various RH levels before carrying out a microindentation grid. Their microstructure was statistically characterized in terms of indentation modulus (M) and hardness (H), as well as the contact creep modulus (C), which was analyzed by a logarithmic contact creep compliance in time. The effects of RH and porosity on the microindentation parameters (M, H, and C) were then characterized and compared to those measured on synthetic C–S–H and a cement paste, which are available in the open literature. Finally, a simplified analysis showed that the creep rate is linearly dependent on RH, thus confirming the importance of the sliding of calcium silicate sheets structure on the long-term basic creep of layered C–S–H minerals.
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