Corrosion of Embedded Carbon Steels, Carbonation and Chloride Diffusion in Low-Clinker Hybrid and LC3-50 Cements: A Critical Review

Portland cement (PC) is responsible for about 7–9% of the CO2 emissions worldwide. Alkali-activated materials (AAMs) are alternatives that have been intensely researched in recent decades, but some of their characteristics have hindered their extensive use in construction. Hybrid cements (HCs) and limestone calcined clay cements (LC3-50) are other, more innovative alternatives to PC, which seem easier to implement. Nowadays, there is active research about them, and pioneering studies about the durability of carbon steel reinforcements with these two types of binders are beginning to be published. In this review, the properties of HC and LC3-50 are briefly summarized and related with those of PC and AAMs. The uncertainties implied by using carbonation and chloride diffusion tests designed for PC to compare materials with different compositions are discussed. Using electrochemical methods seems logical to obtain full information about the durability of reinforcements in the innovative binders. However, these alternative binders have special features that can sometimes make the traditional electrochemical approach used yield misleading results. Factors such as the high resistivity some alternative mortars can exhibit, or the possible development of redox processes in the binder due to the nature of the precursors, must be borne in mind.