Passivation of galvanized and carbon steels in phosphate mortarsmanufactured with alternative MgO sources

Abstract

Magnesium potassium phosphate cements (MKPCs) are cementitious materials that harden simplywith water and are very useful for repairing damaged concrete structures. However, obtainingMgO implies high CO2 emissions. In the present study, the MgO is obtained from two differentindustrial by-products (cyclone dust during the industrial calcination of magnesite and tundishdeskulling waste generated in the steel manufacturing), as they can be an ecological alternative tomanufacture mortars. The properties of these innovative mortars still deserve further research.Moreover, if the MKPCs need to be used for repairs of reinforced building structures or for applicationsthat could involve embedded metal bars, the ability of these mortars to passivate themetal is another key point that is investigated in the present research. The characteristics of thealternative MKPC mortars, such as curing shrinkages, mechanical properties, porosities and pHs,are compared with those of conventional ordinary Portland cement mortar. Ribbed carbon steeland galvanized steel bars were used as reinforcements. Six different types of reinforced mortarsamples were exposed to high relative humidity (RH) for four months and their electrochemicalperformances were monitored. Both carbon and galvanized steels embedded in the highlyecological MKPC mortars manufactured with MgO from tundish wastes are able to be passive inenvironments with high RH. However, galvanized and carbon steel bars are not able to reach astable passivity in mortars made with cyclone dust MgO. Analysis of the pore solutions obtainedafter pore pressing enable these results to be understood.