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

Author(s): Yubo Sun, Yaxin Tao, A. V. Rahul, Guang Ye, and Geert De Schutter

Publication: Materials Journal

Volume: 119

Issue: 6

Appears on pages(s): 233-245

Keywords: alkali-activated slag (AAS) concrete; high-range water-reducing admixture (HRWRA); reaction kinetics; rheology; strength development

DOI: 10.14359/51737192

Date: 11/1/2022

Abstract:
The rapid workability loss of alkali-activated materials (AAMs) has been a major obstacle limiting their on-site application. In this study, two conventional high-range water-reducing admixtures (HRWRAs) (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 that sodium silicate-activated AAS mixtures exhibited lower yield stress than those activated by sodium hydroxide. In hydroxide media, PNS and LS remained effective in reducing yield stress and increasing 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 either activator, although LS showed a retardation effect and subsequent increase in the setting time in the fresh state.