Microrheology of fresh geopolymer pastes with different NaOH amounts at room temperature

Abstract Microrheology is employed to continuously measure the viscoelasticity of fresh geopolymer pastes with disturbances under different NaOH amounts at an early age. In this study, the elastic index (EI), macroscopic viscosity index (MVI), storage modulus G′, and loss modulus G″ were computed to quantitatively analyse the viscoelastic properties of fresh geopolymer pastes based on the mean square displacement (MSD) of the particles. The results indicate that EI, MVI, and G′ of fresh geopolymer pastes dramatically increase over time initially, and then reach equilibrium. When the amount of NaOH is below 10%, an increase in the NaOH amount significantly improves the growth rate of the elastic properties, which is attributed to the formation of Si–O–Na bonds resulting in changes in the aluminosilicate gel. Beyond 10% NaOH, the surfaces of particles covered by a new layer of darker film delays the geopolymerization and development of the elastic properties.