Duality between Creep and Relaxation of a Cement Paste at Different Levels of Relative Humidity: Characterization by Microindentation and Analytical Modeling

Recent studies have showed that microindentation techniques allow assessing the logarithmic creep rate of a cement paste in good correlation with the long-term creep rates measured by compressive tests at macroscopic scale. After having applied microindentation techniques to characterize the effect of relative humidity (RH) on both the creep and relaxation behavior of a cement paste, the objective of this work is to analyze the duality between creep and relaxation curves by means of the analytical models which are currently employed in open literature. First, large grids of creep and relaxation microindentation tests were carried out on a cement paste sample in hygral equilibrium at different levels of RH. Thus, the results were modeled by a viscoelastic model by considering different creep functions (logarithmic and power-law) and corrective terms for initial plasticity under loading. The presented results provide new insights to understand the duality between creep and relaxation rates of a cement paste measured at micrometer scale, especially considering the possible plastic effect.