VISUALIZATION OF HYDROPHOBIC COMPOUND DISTRIBUTION IN HARDENED CEMENT PASTE USING X-RAY CT

Although hydrophobic compounds have been reported as an effective method for improving frost resistance of concrete, little research has been undertaken to investigate the behavior of hydrophobic compounds in hardened cement paste (HCP). Moreover, by using the existing cross-sectional observation approach to investigate the air void system in HCP, it is unclear how oil droplets exist in the HCP, and distinguishing between air bubbles and droplets becomes difficult. In this study, silicone oil and paraffin were used as the hydrophobic compounds. The behavior of silicone oil and paraffin in the HCP was investigated using X-ray computer tomography (CT) as a non-destructive method to elucidate the mechanism of suppressing frost damage. The findings demonstrated that it is clearly possible to distinguish between oil droplets and air bubbles in the HCP containing silicone oil. Furthermore, we could also observe how oil droplets disappeared and changed into voids during the hardening process. In contrast, the HCP containing a paraffin admixture was unable to distinguish between air bubbles and paraffin.