Short-term creep of cement paste during nanoindentation

Current research interest in multi-scale modeling of cement paste requires accurate characterization of the time-dependent mechanical properties of the material, particularly the C–S–H phase. Nanoindentation is evaluated as a tool for measuring the short-term viscoelastic properties of cement paste. A time-dependent solution derived using the elastic–viscoelastic correspondence principle is used to characterize creep indentation tests performed on hardened cement paste and to extract the time-dependent properties. The effect of approximating C–S–H viscoelastic properties with a time-independent Poisson’s ratio or time-independent bulk modulus is discussed, and arguments for utilizing a time-independent Poisson’s ratio for short-term response are presented. The measured nanoindentation creep results indicate a trimodal trend both in the displacement versus time response of the test data and also in the extracted viscoelastic uniaxial compliance. Expressions for the mean short-term viscoelastic uniaxial compliance of C–S–H are given and a probability density function of the viscoelastic Young’s modulus is plotted.