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Creep effects in nanoindentation of hydrated phases of cement pastes

机译：蠕变效应对水泥浆水合相纳米压痕的影响

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This paper focuses on the nanoindentation of cement pastes and their micromechanical response. Since cement paste is a heterogeneous material at microscale, micromechanical properties have to be assessed separately for its individual material phases, i.e. hydrated products and unhydrated phases. Our study addresses important issues concerning experimental loading paths and their effects on the evaluation of elastic properties using nanoindentation. The effect of creep is shown on a series of multicycle experiments. A wide range of maximum loads and corresponding final penetration depths (approximately 200-1200 nm) are covered in this study. Experimental measurements on both hydrated cement samples and on unhydrated clinker minerals have proved that significant creep deformation can be attributed purely to hydrated phases. Further, it has been found that cement paste exhibits a strong size effect on elastic properties measured by nanoindentation and evaluated by the standard Oliver-Pharr procedure for loading-unloading tests with no dwell period at the peak load. Such property was already reported for plastic materials like metals [Elmustafa AA., Stone DS., Indentation size effect in polycrystalline F.C.C. metals, Acta Materialia 2002; 50 (14): 3641-3650., Wei, Y., Wang, X., Zhao, M., Size effect measurement and characterization in nanoindentation test, Journal of Material Research 2004; 19 (1): 208-217.], due to various effects but creep. As shown in the paper, cyclic loading and using long dwell periods at peak load leads to minimizing of this spurious type of size effect. Moreover, comparison with results obtained for the COC/PE polymer (75 percent cycloolefin copolymer+25 percent polyethylene) has been performed. This polymer has been found to exhibit similar time-dependent behavior as hydrated cement paste.
机译：本文重点研究水泥浆的纳米压痕及其微机械响应。由于水泥浆在微观上是一种非均质材料，因此必须分别评估其各个材料相（即水合产物和非水合相）的微机械性能。我们的研究解决了有关实验加载路径及其对使用纳米压痕评估弹性性能的影响的重要问题。一系列多周期实验显示了蠕变的影响。这项研究涵盖了广泛的最大载荷和相应的最终穿透深度（约200-1200 nm）。对水合水泥样品和未水合熟料矿物进行的实验测量已证明，明显的蠕变变形可完全归因于水合相。此外，已经发现水泥浆对通过纳米压痕法测量并通过标准的Oliver-Pharr方法进行的用于卸载实验的弹性性能表现出强烈的尺寸效应，该测试在峰值载荷下没有停留时间。已经报道了诸如金属之类的塑料材料的这种性能[Elmustafa AA。，Stone DS。，多晶F.C.C中的压痕尺寸效应。金属，Acta Materialia 2002; 50（14）：3641-3650。，Wei，Y.，Wang，X.，Zhao，M.，纳米压痕测试中的尺寸效应测量和表征，《材料研究杂志》 2004年; 19（1）：208-217。]，由于各种作用而蠕变。如论文所示，周期性加载和在峰值负载下使用较长的停留时间可最大程度地减小这种杂散类型的尺寸效应。而且，与获得的COC / PE聚合物（75％的环烯烃共聚物+ 25％的聚乙烯）的结果进行了比较。已经发现这种聚合物表现出与水合水泥糊相似的时间依赖性行为。

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