Field studies of chloride transport into high-performance concrete

High-performance concrete slabs have been field exposed at the Traslovslage marine field station at the Swedish west coast since April 1992 as a part of the Cementa/Euroc sponsored project, "Durability of Marine Concrete Structures." The concrete slabs mounted on a floating pontoon are exposed in three exposure zones: submerged, splash, and upper splash zones. The results after two years of exposure confirmed the expected inverse relationship between chloride ingress and water-to-binder ratio. The use of five to 10 percent silica fume in the binder had a very positive effect on reducing the chloride ingress, but no benefit at all was found for concrete with fly ash in the binder as compared to the use of five percent silica fume. Generally, the results indicated that high-performance concrete may be regarded as extremely resistant to degradation by reinforcement corrosion, as long as effects of cracks are not considered. The extremely low levels of chloride ingress in the high-performance concrete indicated that the service life in practice will be decided by the properties of defects in the concrete microstructure. As a consequence, it was recommended that durability research on high-performance concrete should address the effects of cracks, of voids at the steel surface, and of other defects in the microstructure on the long-term performance. Such studies are currently being undertaken in Sweden, Norway, and Denmark.