Experimental and numerical study of anomalous moisture transport in cement-based materials

Research Background

The degradation process of cement-based materials is largely governed by moisture transport, which is generally modeled through the classic flow theory for porous media. However, experimental data on moisture transport in both wetting and drying of cement-based materials often disagrees with the classic theories, making predictions for moisture transport unreliable. The observation that moisture transport in cement-based materials deviates from classical flow theory is generally summarized under the term “anomalous” moisture transport.

Anomalous moisture transport might result from two main causes: (1) the specific “water sensitivity” of cement-based materials. Previous studies have shown that both drying and wetting can lead to obvious microstructural alterations of cement-based materials; (2) the different transport mechanisms in pores with different sizes. 

Aims and objectives

This project aims at examining the above-mentioned causes of anomalous moisture transport by both experimental and numerical studies. Moisture transport models are proposed to consider the microstructural changes upon wetting and drying, and different transport mechanisms. Measured data of water absorption measurements are used to calibrate the proposed models.

Methodology

The “water sensitivity” of cement-based materials is included in the model by the time-dependent water permeability. Modern experimental techniques will be employed to characterize the microstructural alterations during moisture transport. These results will be the basis of the new moisture transport model that combines the effect of microstructural alterations with the classic flow theory.

The transport mechanisms in pores with different sizes are considered by the dual-permeability concept. Specimens with specially designed geometry will be used in water absorption measurements to magnify the transport difference between different sizes of pores. Therefore, the transport concept can be verified.

In addition to the above-mentioned concepts, pore-scale imaging and modeling will be used to improve fundamental understanding of moisture transport in cement-based materials, as well as to improve the development of macroscale transport models. High-resolution imaging techniques, such as XRμCT and FIB-SEM, will be used to characterize complex pore space geometry, while direct numerical simulation of multiphase flow will be used to predict pore-scale moisture transport while preserving the complexity of the geometry.