A long-term study on the effect of a hydrophobic treatment on the moisture balance and durability of a reinforced concrete structure in a road tunnel

Abstract

Concrete structures in the vicinity of seawater or deicing salts on roads in regions with cold climatic conditions, are exposed to chlorides. Transport of chlorides in concrete due to capillary suction during drying and wetting cycles as well as diffusion in combination with carbonation tends to result in corrosion of the rebar and loss of structural integrity. This damage mechanism mainly applies to directly weathered components. After a longer service life, however, components that are not directly exposed, such as concrete surfaces outside the spraying water area of a tunnel, are also affected. A long-term study over 12 years was performed to investigate the effect of hydrophobic treatment on the moisture balance and durability of a suspended tunnel ceiling compared to an untreated surface with the same exposure. Embedded sensors installed in the concrete structure and an online monitoring system were used to measure the electrical resistivity of the concrete and the corrosion rate of the steel reinforcement over time. Furthermore, the data obtained were combined with climate measurements in the tunnel to gain new insights on the effect of tunnel climate on the damage mechanism. The measurements allowed to prove the long-term effect and correct application of hydrophobic treatment. With these results it is possible to make a more precise estimation of the condition and the deterioration process of the tunnel ceiling and to optimize the rehabilitation schedule.