Transfer properties and chloride-induced corrosion resistance of GGBS and metakaolin alkali-activated materials

This study compares the resistance against chloride-induced steel corrosion of two alkali-activated materials (AAMs) and a CEM III concrete. The AAMs studied are: a metakaolin activated with sodium silicate (AAMK), and a GGBS activated by sodium carbonate (AAS). In order to study the corrosion of the reinforcement due to chloride, electrochemical measurements were performed on reinforced samples kept in a humid room (passive conditions) and samples dried (40 degrees C) before their immersion in a 35 g/l chloride solution (active conditions). AAMK showed the highest transfer properties whereas AAS and CEM III showed similar performance. The highly interconnected porous network of AAMK concrete presented low resistance to the penetration of chloride ions and very low resistivity compared to CEM III and AAS concrete. AAS had a finer porosity and a high chloride fixation capacity, which led to better resistance to chloride penetration and high resistivity. However, in AAS, sulfide ions from the slag dissolution led to low corrosion potential compared to values measured in traditional concrete. The drying of these samples at 40 degrees C caused a drop in the resistivity and a sharp increase in the chloride migration coefficient, which was explained by damage of the material. No corrosion products were observed after 2 years on rebars embedded in AAMs (AAMK and AAS). However, in CEM III reference concretes, pits of corrosion were identified when the reinforced samples were split. AAMs seemed to provide good protection of the reinforcement regarding chloride corrosion in immersed samples.

Automated summary

This study compared the resistance to chloride-induced steel corrosion between two alkali-activated materials (AAMs) and a CEM III concrete. The results showed that the AAMK, activated with sodium silicate, had the best chloride penetration resistance and lowest resistivity compared to CEM III concrete. The AAS, activated with sodium carbonate, had finer porosity and higher chloride fixation capacity, resulting in better chloride resistance and high resistivity. However, the AAS also had low corrosion potential due to sulfide ions from slag dissolution.