Quantification and Modelling of the Saturation Behaviour of Hardened Cement Paste During Frost Attack By Means of Innovative NMR Imaging

由于冻融作用，硬化水泥浆体基质中的水分迁移对混凝土的抗冻性有很大影响。暴露强度是孔隙系统饱和度的直接函数。每一次冻融循环都会导致饱和度的增加。当达到饱和临界值时，就会发生结构损伤。本项目旨在量化这一所谓的吸霜过程，将其作为硬化水泥浆体质量和普遍环境条件的函数，并考虑潜在的物理机制。将使用一维核磁共振成像方法对霜吸进行非破坏性分析。从而首次为建立作为霜冻暴露函数的饱和过程预测工程模型提供了依据。调查将在配备单面温度控制的低场核磁共振设备中进行。利用二维核磁共振方法，可以实现良好的空间分辨率以及对快速信号衰减的监测。信号衰减受观察到的水分子的聚集状态和表面相互作用的影响。核磁共振方法的进步将对多孔介质的研究产生普遍的兴趣。

Frost resistance of concrete is significantly influenced by water transport in the matrix of hardened cement paste as a consequence of freezing and thawing action. The intensity of exposure is a direct function of degree of saturation of the pore system. Every freeze-thaw-cycle leads to an increased saturation. Upon reaching a critical value of saturation structural damage occurs. The presented project aims at a quantification of this so called frost-suction process as a function of hardened cement-pasted quality and prevalent environmental conditions considering the underlying physical mechanisms. Frost suction will be analyzed non-destructively using methods of one-dimensional NMR imaging. Thereby for the first time a basis for the derivation of an engineering model for the prediction of saturation process as a function of frost exposure will be provided. Investigations will be conducted in situ in a low-field NMR apparatus equipped with single-sided temperature control. Using two-dimensional NMR methods, a good spatial resolution as well as a monitoring of fast signal decay is to be achieved. Signal decay is governed by state of aggregation as well as surface interaction of the observed water molecules. Advancements of NMR methodology will be of general interest for research on porous media.