Abstract Cement and clays are proposed as sealing materials in underground repositories for radioactive waste. When cement and clay come into contact, chemical gradients between their very different porewater compositions lead to diffusive exchange of solutes, which can result in mineral transformations and alterations of transport properties at the material's interface. Small samples of cement-clay interfaces were prepared and let react over a period of six years. During this time, the changes in transport properties of the samples were periodically monitored by means of through-diffusion experiments. This technique allows studying the evolution of the diffusive flux across the reacting interface and characterizing the variation of the corresponding effective diffusion coefficient (De) over time. All experiments were performed on samples consisting of a hardened high porosity OPC paste and Na-montmorillonite. These model materials were chosen in order to simplify the mineralogy of the system. The experiments allowed obtaining relevant information regarding the development of the diffusive properties and the reactivity of such a cement-clay interface system. HTO and 36Cl− were used as tracers to study the evolution of both the total and the anion accessible porosity. After six years of reaction a considerable reduction of the flux for both HTO and 36Cl− was observed. The flux of HTO did, however, not approach zero, which means that connected porosity for diffusive transport of water is still available. The periodic monitoring of the sample evolution showed a strong reduction of the effective diffusion coefficient De of the samples within the first 1.5 years of the experiment and a less prominent decrease in the period between 1.5 and 6 years. The De of 36Cl− showed a stronger reduction compared to that of HTO; for some cells no chloride flux at all could be measured anymore at t > ∼4 a. Using additional information on the extension of porosity changes from a neutron imaging study performed in parallel on the same samples, the diffusive properties of each component of the interface, or of a clay zone with reduced porosity could be estimated. For HTO the relation between the evolution of De and of the porosity in the clay part can be well described with Archie's empirical law. For chloride large uncertainties regarding the accessible porosity do not allow a precise correlation. Whether a complete porosity clogging will take place or some fraction of connected pore space will persist in the sample over reaction times ≫ than 6 years remains an open question.

中文翻译：

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HTO 和 36Cl− 扩散通过反应性水泥-粘土界面（OPC 糊剂-Na 蒙脱石）在 6 年内的演变

摘要 水泥和粘土被提出作为放射性废物地下处置库的密封材料。当水泥和粘土接触时，它们非常不同的孔隙水成分之间的化学梯度会导致溶质的扩散交换，这可能导致材料界面处的矿物转化和传输特性的改变。制备了水泥-粘土界面的小样本，并在六年内反应。在此期间，通过扩散实验定期监测样品传输特性的变化。该技术允许研究穿过反应界面的扩散通量的演变，并表征相应有效扩散系数 (De) 随时间的变化。所有实验均在由硬化的高孔隙率 OPC 糊料和 Na-蒙脱石组成的样品上进行。选择这些模型材料是为了简化系统的矿物学。实验允许获得关于扩散特性的发展和这种水泥-粘土界面系统的反应性的相关信息。HTO 和 36Cl− 被用作示踪剂来研究总孔隙率和阴离子可及孔隙率的演变。反应六年后，观察到 HTO 和 36Cl− 的通量显着降低。然而，HTO 的通量并未接近于零，这意味着用于水扩散传输的连通孔隙率仍然可用。对样品演化的定期监测表明，样品的有效扩散系数 De 在实验的前 1.5 年中大幅降低，而在 1.5 至 6 年期间降低不那么明显。与 HTO 相比，36Cl− 的 De 表现出更强的还原性；对于某些细胞，在 t > ～4 a 时根本无法测量氯化物通量。使用在相同样品上并行进行的中子成像研究中关于孔隙度变化扩展的附加信息，可以估计界面每个组分或孔隙度降低的粘土区域的扩散特性。对于 HTO，De 演化与粘土部分孔隙度之间的关系可以用 Archie 经验定律很好地描述。对于氯化物，关于可及孔隙度的大不确定性不允许精确的相关性。在反应时间 ≫ 超过 6 年的反应时间内，是否会发生完全孔隙堵塞或部分连通孔隙空间将持续存在于样品中仍然是一个悬而未决的问题。