Passivation of Steel Reinforcement in Low Carbon Concrete

Both the high CO2 emissions associated with cement production and the increasing demand for concrete call for the use of binder types that can be produced in a more climate-friendly way than that of ordinary Portland cement. To ensure that these binders can also be used in reinforced concrete structures, their influence on the corrosion behavior of embedded steel reinforcement must be investigated. In the study presented here, the passivation behavior of steel in mortars made from various new types of binders is investigated. In addition to alkali-activated materials with high and low calcium contents, a calcium sulfoaluminate cement and a binder produced from calcium silicate hydrate (C-S-H) phases, synthesized in an autoclave, were investigated. While the steel clearly passivated in the alkali-activated slag and the C-S-H binder, the calcium sulfoaluminate cement showed the lowest open circuit potentials and polarization resistances, indicating a less effective level of passivation. The metakaolin geopolymer with a potassium-based activator showed an onset of passivation that was dependent on the environment of the specimens at an early age, whereas the alkali-activated fly ash with a sodium-based activator showed a delay in passivation that was not influenced by the environment of the specimens at an early age.