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Micro-X-ray diffraction and chemical mapping of aged interfaces between cement pastes and Opalinus Clay
Applied Geochemistry ( IF 3.4 ) Pub Date : 2020-04-01 , DOI: 10.1016/j.apgeochem.2020.104538
Ellina Bernard , Andreas Jenni , Martin Fisch , Daniel Grolimund , Urs Mäder

Abstract The safety of a geological repository designed for deep storage of nuclear waste rests on the long-lived isolation properties of the geological environment and the engineered barrier system. To study the chemical and physical behaviour of cementitious/clayey interfaces, such interfaces have been collected during repeat sampling campaigns of the CI Experiment (Cement-Clay Interaction Experiment) at the Mont Terri rock laboratory (St. Ursanne, Switzerland, www.mont-terri.ch ) over the last decade. This study focuses on the advanced analysis by μ-XRD mapping to locate and identify the mineral phases on each side of the interface. The hydrates portlandite, ettringite and C–S–H present in the Portland cement (PC) were dissolved in contact with the Opalinus Clay (OPA) up to different depths (~0.2 mm for portlandite; ~1 mm for ettringite; completely depleted for C–S–H up to 0.1 mm and less visible on a 1-mm-depth) while the ettringite from ESDRED (a low-pH cement type) seems to be destabilized to a larger depth (≥3 mm). In contrast to former studies, calcite could not be clearly observed at the interface PC - OPA but was well developed at the interface ESDRED - OPA. The extent of reaction after 10 years is very small in both cases, and dissolution of clay minerals remains below detection. The identification of mineral phases involved in reactions facilitates the understanding of the processes, thus, will help to improve the reactive transport models used to simulate the evolution over long times.

中文翻译:

水泥浆和蛋白石粘土之间老化界面的显微 X 射线衍射和化学映射

摘要 为深储存核废料而设计的地质处置库的安全性取决于地质环境和工程屏障系统的长寿命隔离特性。为了研究胶结/粘土界面的化学和物理行为,在 Mont Terri 岩石实验室(瑞士圣乌尔桑,www.mont-)的 CI 实验(水泥-粘土相互作用实验)的重复采样活动中收集了这些界面。 terri.ch )在过去十年中。本研究侧重于通过 μ-XRD 映射进行高级分析,以定位和识别界面每一侧的矿物相。波特兰水泥 (PC) 中存在的水合物硅酸盐、钙矾石和 C–S–H 在与蛋白石粘土 (OPA) 接触时溶解至不同深度(硅酸盐约 0.2 毫米;钙矾石约 1 毫米;C-S-H 完全耗尽达 0.1 毫米,在 1 毫米深度上不太明显),而来自 ESDRED(低 pH 水泥类型)的钙矾石似乎不稳定到更大的深度(≥3 毫米)。与以前的研究相反,方解石在 PC - OPA 界面处无法清楚地观察到,但在 ESDRED - OPA 界面处发育良好。在这两种情况下,10 年后的反应程度都非常小,粘土矿物的溶解仍然低于检测水平。识别反应中涉及的矿物相有助于理解过程,因此将有助于改进用于模拟长时间演化的反应输运模型。与以前的研究相反,方解石在 PC - OPA 界面处无法清楚地观察到,但在 ESDRED - OPA 界面处发育良好。在这两种情况下,10 年后的反应程度都非常小,粘土矿物的溶解仍然低于检测水平。识别反应中涉及的矿物相有助于理解过程,因此将有助于改进用于模拟长时间演化的反应输运模型。与以前的研究相反,方解石在 PC - OPA 界面处无法清楚地观察到,但在 ESDRED - OPA 界面处发育良好。在这两种情况下,10 年后的反应程度都非常小,粘土矿物的溶解仍然低于检测水平。识别反应中涉及的矿物相有助于理解过程,因此将有助于改进用于模拟长时间演化的反应输运模型。
更新日期:2020-04-01
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