Engineering and micro-properties of alkali-activated slag pastes with Bayer red mud

Abstract

• Red mud alleviates the flash setting phenomenon of AASR pastes. • Red mud exerted a positive effect on the compressive strengths of AASR pastes. • A proper amount of red mud enabled promoting alkali-activation of slag. • RM-donated alkali promoted the gel products formation of AASR pastes. In this study, we produced alkali-activated slag/red mud (AASR) pastes using sodium silicate as the alkali activator. The effects of Bayer red mud (RM) on the engineering and micro-properties of alkali-activated slag pastes were investigated. It was found that the decreased fluidity and the increased setting time of the fresh AASR pastes were achieved through the delayed gel coagulation of RM. The maximum compressive strength of the hardened AASR paste arrived at 89.93 MPa with an optimal proportion (i.e., R40S60). Furthermore, the increases in hydration heat peaks of AASR pastes were observed in some mixes (e.g., R20S80 and R40S60), which verified the appropriate amounts of RM enabled promoting the alkali-activated reaction of slag. Besides, the polymerization and hydration products (C-(N)-A-S-H gels and ettringite) of AASR pastes were elaborated through spectroscopic and micro-morphologic analyses.