Increasing durability of infrastructures is crucial in our current society. Unsaturated water flow, such as capillary imbibition, is a common durability problem in concrete structures. In practice, the rate of water ingress by capillary imbibition (CIR) is an excellent descriptor of the pore structure and could be used as a durability index. However, cementitious materials present an anomalous behaviour compared to bricks or other construction materials: the rate of water uptake decreases more rapidly with time, and the different standardized methods to calculate the CIR are difficult to compare. The main cause of this anomaly seems to be the swelling that occurs inside the microstructure due to the hygroscopic nature of the calcium silicate hydrates (C-S-H), which are the main compounds of hardened cement paste. Measurements of deformations caused by swelling can provide new insights into the transport process. This can be studied by determining the deformation of mixes with different amounts of C-S-H and supplementing this with microstructural analysis. Additionally, changes in structure and morphology of C-S-H when exposed to different moisture and CO2 conditions can provide information of real-life structures exposure. A deeper understanding of this phenomenon will help to propose measures to increase the durability of concrete structures.