Preferred orientation of calcium aluminosilicate hydrate compacts: Implications for creep and indentation
Preferred orientation of calcium aluminosilicate hydrate compacts: Implications for creep and indentation
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DOI：
10.1016/j.cemconres.2021.106371
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发表时间：
2021-02-02
影响因子：
11.4
通讯作者：
Monteiro, Paulo J. M.
中科院分区：
文献类型：
--
作者：
Li, Jiaqi;Zhang, Wenxin;Monteiro, Paulo J. M.
纳米/微米压痕已广泛用于检查水泥基材料的弹性性能和蠕变。然而，测量的弹性模量存在不一致，并且对于硅酸钙（铝）水合物（C-（A-）S-H）的蠕变机制存在争议。为了带来新的见解，我们使用基于同步加速器的 X 射线衍射研究了偏应力引起的硅铝酸钙水合物 (C-A-S-H)、硅酸钙石和钙矾石复合体的择优取向。在C-A-S-H压坯中观察到强烈的择优取向，并且晶胞的c轴与压缩方向高度一致；在硅钙石和钙矾石中形成较弱的 c 轴相关纤维型织构。较高的湿度、较大的压实压力和/或增加的压力持续时间增强了C-A-S-H的优选取向，这是通过凝胶孔水润滑促进的。这种压力引起的与时间相关的微晶优先重新取向会导致水泥基材料的蠕变，并且可能导致纳米压痕实验中 C-(A-)S-H 晶胞的软 c 轴的过度表征和杨氏模量的低估。
Nano/micro-indentation has been extensively used to examine elastic properties and creep of cement-based materials. However, there have been inconsistencies in the measured elastic moduli and debate on the creep mechanism of calcium (alumino) silicate hydrates (C-(A-)S-H). To bring new insights, we examined the deviatoric stress-induced preferred orientation of calcium aluminosilicate hydrate (C-A-S-H), portlandite, and ettringite compacts, using synchrotron-based X-ray diffraction. Intense preferred orientations were observed in C-A-S-H compacts, and the c-axis of unit cells is highly aligned with the compression direction; weaker c-axis related fiber-type texture formed in portlandite and ettringite. Higher humidity, greater compacting pressure, and/or increased duration of the pressure intensified the C-A-S-H preferred orientation, which is facilitated by gel-pore water lubrication. This pressure-induced time-dependent preferential re-orientation of crystallites can contribute to the creep of cement-based materials, and it may cause overrepresentation of the soft c-axis of C-(A-)S-H unit-cell in nanoindentation experiments and underestimation of Young's modulus.