Strategies for control and mitigation of efflorescence in metakaolin-based geopolymers

Efflorescence can be harmful to material performance as a consequence of microstructural changes due to leaching and carbonation of alkalis. This article identifies mechanisms of efflorescence in metakaolin-based geopolymers, and approaches to reduce free/mobile alkali cations and pore network connectivity, and hence reduce efflorescence. Mechanical, mass transport and microstructural properties are assessed in metakaolin-based geopolymer cements produced using different alkali concentrations in the alkali activator and substitution/addition of blast furnace slag, silica fume, calcium aluminate cement, silicone oil and a dispersive admixture. The most effective strategy to reduce efflorescence results from increasing Si/Al in the geopolymer gel by addition of soluble silicate, silica fume or silicone oil. Addition of calcium aluminate cement or a dispersive admixture also reduce efflorescence, but are less effective. These results confirm that efflorescence may be reduced by controlling the amount of soluble silicates and reducing free alkali cations in geopolymers, providing enhanced performance and durability.

Automated summary

Efflorescence in metakaolin-based geopolymers can be reduced by increasing the Si/Al ratio in the geopolymer gel, controlling soluble silicate content, and reducing free alkali cations. Addition of soluble silicate, silica fume, or silicone oil is the most effective strategy to reduce efflorescence, while calcium aluminate cement or a dispersive admixture are less effective. These results confirm the importance of controlling soluble silicates and alkalis in geopolymers for enhanced performance and durability.