Synthesis and properties of a novel structural binder utilizing the chemistry of iron carbonation

This paper explores, for the first time, the possibility of carbonating waste metallic iron powder to develop sustainable binder systems for concrete. The fundamental premise of this work is that metallic iron will react with aqueous CO2 under controlled conditions to form complex iron carbonates which have binding capabilities. Chosen additives containing silica and alumina are added to facilitate iron dissolution and to obtain beneficial rheological and later-age properties. Water is generally only a medium for mass transfer in these systems thereby making the common reaction schemes in portland cement concretes inapplicable. The compressive and flexural strengths of the chosen iron-based binder systems increase with carbonation duration and the specimens carbonated for 4 days exhibit mechanical properties that are comparable to those of companion ordinary portland cement systems that are most commonly used as the binder in building and infrastructural construction. The influence of the additives, carbonation duration, and the air curing duration after carbonation are explored in detail. Thermogravimetric analysis demonstrate the presence of an organic carbonate complex (the dissolution agent used to dissolve iron is organic), the amount of which increases with carbonation duration. Thermal analysis also confirms the participation of some amount of limestone powder in the reaction product formation. The viability of this binder type for concrete applications is proved in this study.