Diffusion potentials in non-saturated, porous mineral materials – error and information source

在混凝土或土壤等多孔材料中，由于环境暴露，孔隙溶液很可能在化学成分上表现出空间差异。因此，存在扩散电位，并且可以很容易地达到几十毫伏或超过100 mV。与伴随的阳离子相比，阴离子的迁移率较高，因此在pH的梯度中有很大的影响。多孔矿物材料中的扩散势在研究和实践中对测量有重要影响。因此，这可能会导致对结果的相当大的误解，并最终影响评估。目前的技术水平允许预测饱和、多孔矿物材料中的扩散势。我们将继续进一步研究具有渗透选择行为的非饱和材料中的扩散势。这个项目的总体目标是显著提高目前对多孔矿物材料中扩散势的理解，特别是在水泥基材料和沙质土壤中。其目的是提高基于材料特性和曝光条件的扩散势预测的准确性。主要感兴趣的情况是氯化物暴露引起的条件以及碳化或淋滤引起的pH值差异。到目前为止，考虑的是饱和材料。在实践中，如果结构没有被水淹没，混凝土通常是非饱和的。因此，这种状态比饱和状态具有更高的实际意义。实验测量(TUM)和数值模拟(ETHZ)相结合是开发扩散势预测工具的基础。进行了扩散电势的测量。正在研究的材料的表征(孔隙率、水分含量)将通过压汞测孔法、核磁共振弛豫法、电化学阻抗谱进行。离子浓度梯度的测定将通过激光烧蚀电感耦合等离子体质谱(LA-ICPMS)等方法进行。数值模拟基于Poisson-Nernst-Planck方程，在扩散势为误差源的情况下，能够预测扩散势是应用适当校正的关键。此外，更好地了解材料的渗透选择特性及其对扩散势的影响也可以利用扩散势的测量作为获得所研究材料的信息的一种手段。几项工程任务和当前的研究将受益于发展扩散势预测的科学基础。这包括电位测量、腐蚀监测和阴极保护。

In porous materials such as concretes or soils, the pore solution is likely to exhibit spatial differences in chemical composition in cause of environmental exposure. Thus, diffusion potentials are present and may easily reach several tens of millivolts or exceed 100 mV. A major influence has been identified in gradients of pH due to the higher mobility of anions in comparison to the accompanying cations.Diffusion potentials in porous mineral materials have a significant effect on measurements in research and practice. Consequently, it may lead to considerable misinterpretation of the results and eventually affects the assessment. The present state of the art allows prediction of diffusion potentials in saturated, porous mineral materials. We will continue with further study considering diffusion potentials in non-saturated materials with perm-selective behavior.The overall objective of this project is to significantly improve the current understanding of diffusion potentials in porous mineral materials, particularly in cement-based materials and in sandy soils. The aim is to enhance the accuracy of predictions of diffusion potentials based on material properties and exposure conditions. The situations of main interest are conditions arising from chloride exposure as well as pH differences due to carbonation or leaching. So far, saturated materials were considered. In practice, concrete is normally non-saturated, if structures are not submerged in water. Therefore, this condition state is of higher practical relevance than the saturated state. Consequently, the aim is the development of a tool to predict diffusion potentials in case of non-saturated concrete.The combination of experimental measurements (TUM) with numerical simulations (ETHZ) is the basis for developing the predictive tool for diffusion potentials. Measurement of diffusion potentials is carried out. Characterization (porosity, moisture content) of materials under study will be done by mercury intrusion porosimetry, nuclear magnetic resonance relaxometry, electrochemical impedance spectroscopy. Determination of ion concentration gradients will be done by methods such as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Numerical simulations are based on Poisson-Nernst-Planck equations.Being able to predict diffusion potentials is crucial to apply adequate corrections in case of diffusion potential is an error source. Furthermore, an improved understanding of the perm-selective properties of the material and their influence on diffusion potentials may also allow using measurements of diffusion potentials as a means to obtain information about the material under study. Several engineering tasks and current research will benefit from developing the scientific basis for the prediction of diffusion potentials. This includes potentiometric measurements, corrosion monitoring, and cathodic protection.