Transforming calcium carbonate–silicate wastes into steel protective coatings

•Sodium silicate solution was mixed with calcium carbonate to yield a steel-protective coating.•Using silicate-rich-wastes as alternative to sodium silicate enhanced the behavior of coating.•Applying nanomagnesia-modified coating enhanced the resistance of steel to chloride corrosion. This work focused on developing an innovative steel protective coating, in which calcium carbonate (CC) is the primary precursor. Mixing sodium silicate solution with CC-powder induced calcium silicate hydrate (CSH) formation binding phase via the cationic exchange reaction. Incorporating lead glass sludge and glass waste, as environmentally friendly silicate rich source alternative to sodium silicate, enhanced the creation of CSH binding phase, which is associated with an increase in the compaction of the resulted coating’s microstructure. Using prepared coatings on the surface of steel rebars improved their resistance to chloride-induced corrosion. The coated steel containing lead glass sludge was found to represent the higher affinity to mitigate chloride diffusion, as it recorded polarization resistance (Rp) (480 kΩ/cm2) higher than that reference steel reinforcement (39 kΩ/cm2) at 3 months of immersion in seawater. Utilizing nano magnesia (nM) as an additive to the protective coating with lead glass sludge results in a further improvement in the coated steel against chloride-induced-corrosion. An additional magnesium silicate hydrate (MSH) binder was formed, resulting in remarkable improvements in the compactness of the coating's microstructure. This innovative approach is different from traditional methods for producing reactive calcium oxide through thermal treatment of CC at higher temperatures. Reactive calcium is produced through the cationic exchange reaction at room temperature, reflecting a reduction in CO2 emissions, minimizing processing costs and energy demands. Unlike the alkali-activated aluminosilicate-based coatings, the prepared coatings represent high commercial viability and low cost. Additionally, due to the properties of calcium carbonate, which are independent of its source, these coatings can be globally standardized. However, before applying this coating to different surfaces, it is crucial to address its mechanical properties and durability against various aggressive media. These aspects will be the primary focus of our future work.