Mechanochemical synthesis of one-part alkali aluminosilicate hydraulic cement

Abstract

A novel approach was devised to synthesize a sustainable hydraulic cement based on alkali aluminosilicate chemistry via mechanochemical activation. This approach builds upon past work on activation of aluminosilicate precursors using alkaline solutions to produce inorganic binders for concrete construction. Recent efforts to develop one-part hydraulic cements based on the chemistry of alkali-activated aluminosilicates have resorted to high-temperature processing techniques which compromise the sustainability advantages of the system, and also require curing at elevated temperatures. The mechanochemical process developed here takes place at room temperature, and yields a hydraulic cement that does not require addition of caustic solutions to render binding effects via room-temperature curing. Processing of this hydraulic cement takes place at room temperature; this advantage together with extensive use of recycled raw materials yield significant sustainability benefits. The (dry) raw materials used for mechanochemical processing of hydraulic cement included coal fly ash, quick lime, sodium hydroxide and Magnesium oxide. The mechanochemically processed hydraulic cement was evaluated through performance of tests concerned with their pH, heat of hydration, chemical composition, crystallinity and microstructure. The hydraulic cement was used to produce concrete materials cured at room temperature. The resulting concrete materials were found to provide desired levels of workability in fresh state and compressive strength after curing, which were comparable to those of Portland cement concrete. Investigations were also conducted on the hydration kinetics of the hydraulic cement and the microstructure of its hydrates in order to gain insight into its hydration process and the nature of hydration products.