Stability of superplasticizer on NaOH activators and influence on the rheology of alkali-activated fly ash fresh pastes

Abstract

This paper investigates the effect of the five different superplasticizer (SPs), Melamine sulfonate (M), naphthalene-based (N), lignosulfonate (L), polyether-type (P-Ⅰ), and polyester-type polycarboxylate super-plasticizers (P-Ⅱ), on the rheology of fly ash pastes activated by different molarity of NaOH activator. The fluidity, viscoelasticity, inter-microstructure, and mechanism were evaluated for AAM fresh pastes. And the stability of SPs in the different molarity (0.01 M, 0.1 M, 1 M, 2 M, 3 M,5 M, and 10 M) of NaOH activators was investigated by the ATR-FTIR experiment. The results show that all SPs were the effective admixtures under low molarity (0.1 M) of NaOH activators, while N-SPs performed better in case of high molarity (10 M) of NaOH activators in AAM fly ash pastes. However, with the increase in the concentration of NaOH activators, the structure of SPs is destroyed into small molecules and has negligible effects on the rheology properties of fresh pasts. Unlike other SPs, the electrophilic effect of Ar and strong electricity of the sulfonic acid group of N-SPs may provide more adsorption sites and decrease the interaction between sulfonic groups.