Chloride detection in cement based materials by ultrasonic interferometry.

Chloride ions play an important role in the corrosion of steel reinforcement in concrete structures. In northern countries, de-icing salts are a major factor in the deterioration of highways, and in many countries, chlorides from seawater exacerbate the deterioration process. In order to assess the chloride penetration as destructive, low spatial resolution methods are routinely used. A range of ultrasound based techniques are currently being used to characterize cement based materials. However, they are intended primarily to monitor changes in mechanical properties, cracking, position of stressing tendons, and corrosion of reinforcement. This paper will demonstrate the ability of an ultrasonic interferometry technique to monitor the capillary absorption of a 16.5% NaCl solution in cement paste and mortar cube samples. The results demonstrate that this technique is able to detect small changes in the properties of fluids penetrating the porous material. Future applications will include imaging of chloride penetration in cement based materials in laboratory and field conditions.