Prediction of micro creep behavior of hardened cement paste based on the isotache model of clays

Cement-based material is a strain-rate-sensitivity material, understanding of the strain rate effect on the mechanical properties and deformation of cement-based materials fully can ensure safe design of concrete structures with enhanced performance. The micro creep of hardened cement pastes under different strain rates were investigated by performing continuous stiffness measurement. The (water to cement) w/c ratios of hardened cement pastes were 0.3, 0.4, and 0.5. The maximum indentation depth during the CSM was set as 30 μm and the applied strain rates were 0.01 s^-1, 0.05 s^-1, 0.1 s^-1, and 0.5 s^-1. The results show that a unique h_vp-P-ε relationship is found for hardened cement paste under the strain rates ranging between 0.01s^-1 and 0.5 s^-1 at microscale. This is analogous to the unique ε_vp-σ-ε relationship for clays. The h_vp-P-ε relationship can be simply described by two sets of curves:the P_N/P_N0.05-ε curve and the normalized h_vp-P/(P_N/P_N0.05) curve. These two curves can be used to predict the h_vp-P curves of cement pastes under any constant strain rate during the loading stage. This finding preliminary confirms the applicability of the isotache approach to characterize the time-dependent deformation of cement pastes at microscale.