Efflorescence Control in Calcined Kaolin-Based Geopolymer Using Silica Fume and OPC

Abstract

Efflorescence has been an ongoing issue facing the development of geopolymers; excess efflorescence may disturb the stability of the binder microstructure. This paper investigates the controlling of efflorescence in a calcined kaolin-based geopolymer binder cured at ambient temperature. Silica fume (SF) and ordinary Portland cement (OPC) were used at different replacement levels (0, 5, 10, and 15 wt.%) to control the efflorescence via microstructural refinement. A digital camera was used to observe the extent of efflorescence on the surface of geopolymer mortars. Several techniques were performed to understand the effects of SF and OPC on the microstructural changes of the geopolymer binders. The bicarbonate and carbonate ion concentrations, as well as the alkalinity of leaching solutions, were measured. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and x-ray diffraction (XRD) tests were used to better understand the microstructural changes. The results revealed that using SF at 5wt.% or OPC at 10% reduces the efflorescence extent with improved compressive strength.