Coatings Based on Light-Weight Alkali Activated Mortars for Steel Corrosion Protection

Alkali activated materials and geopolymers have attracted a lot of attention in the last 20 years thanks to their excellent mechanical performances, durability and sustainability properties, especially for civil applications. These materials also exhibit promising properties as fire- and corrosion-resistant protection systems. In a previous study, a 20-mm coating based on light-weight alkali activated mortar (LWAAM) suitable for the protection of steel structures against fire was successfully developed. To understand if the same coating is also able to ensure corrosion protection to steel structures, this study reports the results obtained in two different chloride-rich environments. The corrosion performance of the new system based on steel coated by LWAAM (using expanded perlite and hydrogen peroxide in the mix) was compared with a steel coated by a traditional alkali activated mortar (NWAAM). Electrochemical tests on steel samples immersed in an alkaline solution simulating the pore environment of the binder or embedded in the two different types of mortars were carried out in presence of different chloride concentrations. It was found that the alkaline environment is able to passivate the steel surface, however, increasing the chloride concentration, the passive film is less stable and promotes steel corrosion. In presence of low chloride concentration (i.e., 0.2M NaCl), the increased porosity of the LWAAM did not impair the steel corrosion protection, when compared with NWAAM.