Alkali-activated binders: Early age nucleation reactions, chemical phase evolution and their implications on system properties

Formation of polymeric cementitious binders via alkaline activation of aluminosilicates has gained significant attention within the manufacturing and building sectors in recent years. Given the diversity of aluminosilicate source materials employed in these systems, such as fly ash, blast furnace slag, calcined kaolinite, etc., the chemistry of raw materials play a crucial role in both kinetics and stability of solid phase evolution which govern chemical and physical properties of resultant products. This paper analyses the effects on elemental composition of raw materials on the overall alkaline activation process; from dissolution to end-product properties. A range of analytical techniques including X-ray synchrotron analysis has been used to characterise amorphous and zeolitic domains from a range of raw materials. In particular, the tendency of aluminosilicate source materials with defined amorphous SiO2/Al2O3 ratios to nucleate sodium aluminosilicate zeolitic phases originating from Na2O–Al2O3–SiO2–H2O gel assemblages is investigated, alongside the dominant influence of Ca ions and residual cationic species based on identifiable compositional domains within ternary phase diagrams. Stable phase assemblages and optimal compositional ranges for different systems are discussed with respect to phase development, microstructural changes and their relationship to long term strength development and chemical resistance.