Sustainable inorganic binders with corrosion resistance properties

Durability is one of the most important issues for building materials, particularly for steel reinforced concrete. When carbon steel reinforcements are used with concrete, the high alkaline environment (pH > 12) generated by cement hydration reactions generally helps the formation of a passivation layer of magnetite (Fe3O4) on the metal surface strongly reducing carbon steel corrosion rate. However, it often happens in civil constructions that large corrosion phenomena easily occur on the reinforcement. Due to its porosity, concrete is not always able to work as protective barrier against the attack of aggressive specimen from outdoor environment thus leading to a lowering of pH and a high corrosion rate of steel rebar. Sustainable binders may replace traditional cement for some applications and increase steel corrosion resistance. Accordingly, the research on supplementary cementing materials (SCM) alkali-activated cements and geopolymers is largely increased in these last years. Many examples of SCM are reported: pulverized soda lime glass, matt waste, rice husk ash, ceramic residues, etc. These new constituents usually replace clinker in different amount (typically 15-35%). On the contrary, alkali activated cements (AAC) and geopolymers (GP) are obtained by silico-aluminates that are chemically activated by high alkaline solutions such as NaOH and sodium silicate solutions. In both AAC and GP, clinker is not present anymore thus making these new types of binder particularly interesting from an environmental point of view.