Efflorescence behavior and mechanism of burnt coal cinder-based geopolymers under different alkali activators

Efflorescence of geopolymers is a common phenomenon, which is caused by overuse of activators and dissolution-crystallization of carbonate. It has been widely focused on, but its behavior and mechanism remain highly disputed. In the study, the behavior and mechanism of four alkali-activated burnt coal cinder-based geopolymers under two curing conditions of intensifying and inhibiting efflorescence was discussed. The study results show that the deterioration of geopolymer properties caused by efflorescence has a strong timeliness and is closely related to the progress of geopolymerization. Furthermore, through comparative verification of performance testing and phases analysis, the direct factor of the degradation of geopolymer properties is not the carbonate produced by excessive alkaline activators. The direct factor of it is that soluble active components (Si, Al or P) are carried to the surface of the geopolymer by the efflorescence substances, resulting in the permanent loss of gel products. Moreover, the efflorescence also shows a complex and close relationship with the types of activator combination, pore structure and curing system. The perception of the association between efflorescence formation and affecting factors provides important insights into the manufacturing and application of geopolymer related materials.