Insights into the efficiency loss of naphthalene superplasticizer in alkali-activated slag pastes

This paper investigates the effect of naphthalene superplasticizer (NS) on the fluidity of four different (activated by Na2SO4, Na2CO3, NaOH and waterglass (WG)) alkali-activated slag (AAS). The adsorption behaviors, solubility, chemical and physical stability, and diffusion properties of NS in alkali activator solutions were comprehensively evaluated. The results indicate that the working efficiency of NS in AAS (at the same Na2O%) followed the order of activators: Na2SO4, Na2CO3 or NaOH, and WG, which losses its efficiency by 45%, 85%, 85%, and 100% when compared to that in slag-water pastes (i.e. using the same saturation dosage of NS as in slag-water paste, 0.75 wt%). In the alkali activator solutions, the NS remained chemically stable; however, it formed micelles and its physical stability reduced. The formation of micelles of NS was clearly captured by transmission electron microscopy (TEM), which is responsible for its lower solubility and mobility in these solutions. The decrease of solubility and mobility of NS in the alkali activator solutions reduced the adsorption and dispersion efficiency of NS in AAS pastes.