基于土体isotache模型的硬化水泥净浆微观徐变预测

水泥基材料是一种应变率敏感性材料，充分掌握水泥基材料的应变率效应对其力学性能和变形的影响可保障混凝土结构的安全设计。采用连续刚度测试（CSM）研究不同应变率下硬化水泥净浆微观徐变特征，试样的水灰比为0.3、0.4和0.5，CSM的最大压入深度为30 μm，应变率分别为0.01 s^-1、0.05 s^-1、0.1 s^-1和0.5 s^-1，并讨论土体的isotache模型表征硬化水泥净浆微观徐变行为的适用性。结果表明，在0.01~0.5 s^-1应变率范围内，微观尺度上的硬化水泥净浆存在唯一的h_vp-P-ε关系，与土体isotache模型的ε_vp-σ-ε关系类似，该关系可由归一化后的h_vp-P/（P_N/P_N0.05）曲线和P_N/P_N0.05-ε曲线来表征。采用h_vp-P/（P_N/P_N0.05）曲线和P_N/P_N0.05-ε曲线可预测不同应变率下硬化水泥净浆加载阶段的h_vp-P曲线，预测结果与实测结果基本吻合，表明可以采用土体的isotache模型来预测硬化水泥净浆微观尺度上的徐变行为。

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.