ABSTRACT
The frost resistance of concrete is highly influenced by the water transport processes in the matrix of the hardened cement paste. Herein the water content of the pores in relation to the pore volume (the so-called degree of saturation) plays an important role. Thus, every freeze-thaw attack provokes an increase of the water content in concrete (the so called frost suction) that can significantly exceed the saturation which is normally reached by capillary suction (Setzer 2001). Upon reaching a critical value of saturation structural damage within the concrete, i. e. the formation of cracks, will occur after one freezing attack (Fagerlund 2004). Hence, when the water saturation behaviour of the hardened cement paste during the frost exposure is understood and the critical degree of saturation is known, it will be possible to predict the time of failure. Relating to laboratory investigations, the critical degree of saturation can be easily determined (Fagerlund 1977). However, the challenge is primarily the quantification of the frost suction process as a function of environmental conditions and material quality considering the underlying physical mechanisms Therefore, it is essential to observe continuously and spatially resolved the water transport in concrete during the freezing and thawing process. A suitable measurement method for the determination of moisture profiles is the Nuclear Magnetic Resonance imaging (NMR). For this analysis method, a special set-up has been developed which allows a non-destructive, highly spatially resolved in situ detection of the water uptake during the frost exposure.
