Effect of High-Range Water-Reducing Admixtures on Alkali-Activated Slag Concrete

Abstract

The rapid workability loss of alkali-activated materials (AAM) has been a major obstacle limiting its onsite application. In this study, two conventional SPs (made of polynaphthalene sulfonate (PNS) and lignosulfonate (LS) salts), which have been reported to be effective in some specific AAM mixtures were separately applied in alkali-activated slag (AAS) concretes. A comprehensive testing program was performed to study their effect on reaction kinetics, rheology evolution, and strength development. Results showed sodium silicate-activated AAS mixtures exhibited lower yield stress than those activated by sodium hydroxide. In hydroxide media, PNS and LS remained effective to reduce yield stress and increase slump value, while they both failed to improve the rheological behavior of AAS activated by silicate. Moreover, the inclusion of 2% admixtures did not result in much strength reduction in both activators although LS showed a retardation effect and subsequent increase in the setting time in the fresh state.