The effect of alkali activator solution on the consistency and setting properties of sustainable geopolymer paste with fly ash and GGBS as blended binder

Abstract

The present study examines the effect of Alkali Activator Solution (AAS) on the consistency and setting properties of the blended binder geopolymer pastes considering the following parameters: (i) geopolymer pastes produced with three different alkali activator ratios (sodium hydroxide: sodium silicate) 1:1, 1:2 and 1:3, (ii) geopolymer pastes produced considering four different molarities of Sodium Hydroxide Solutions (SHS) 2.5M, 5M, 7.5M, and 10M, and (iii) geopolymer pastes produced as blended geopolymer pastes with varying blending ratios of FA and GGBS 30:70,50:50 and 70:30. The consistency and setting characteristics of geopolymer pastes for the 36 different mix combinations were studied. The finding revealed that the molarity of SHS and the ratio of AAS are influencing the consistency and setting characteristics of the proportionately blended FA and GGBS-based geopolymer paste. The increase in the AAS ratio has minimal effect on the consistency of geopolymer pastes except for the geopolymer paste produced with 10M of SHS. The initial and final setting times of geopolymer paste decrease with an increase in the ratio of AAS. The flash setting of geopolymer paste was observed for mixes J3, K3, and L3 which are produced with 10M of SHS and an AAS ratio of 1:3. Microstructural studies such as Scanning Electron Microscopy (SEM) analysis and Fourier Transform Infra-Red Spectroscopy (FT-IR) analysis were carried out. The formation of ettringite was seen in SEM images of FA-rich mixes of geopolymer paste activated with 2.5M molarity of NaOH.