In Switzerland, the main cause of chlorides penetrating into concrete is the use of de-icing salts on roads in winter. If chlorides penetrate into concrete, they can cause severe corrosion of the reinforcement leading to the loss of the load carrying capacity of the structure. To avoid a chloride induced corrosion of the reinforcement different measures can be captured. Beside controlling the thickness of the cover of concrete over the reinforcement or using a coating or water repellent finishing, the use of concrete with a high chloride resistance is very common.
At Empa the influence of the concrete mix design on chloride resistance was investigated. Several concrete mixtures with variations in binder type and water-to-binder-ratio (w/b) were produced. Additionally, for every binder type a mixture of self-compacting concrete (SCC) was investigated. For every mixture, chloride resistance was measured using three different methods:
- Chloride migration coefficient according to standard SIA 262/1, appendix B with an accelerated chloride ingress by applying an electrical field.
- Chloride diffusion coefficient according to standard ASTM C 1556 with natural chloride diffusion by immersing the specimen in chloride solution.
- Chloride conductivity by measuring the electrical current when a known voltage is applied to a specimen which is saturated with chloride solution.