Investigation on a green olivine nano-silica source based activator in alkali activated slag-fly ash blends: Reaction kinetics, gel structure and carbon footprint

In this paper, a green olivine nano-silica is synthesized and applied as an alternative silicate source to prepare alkali activators, and a commercial waterglass based silica source is studied as a reference. The synthesis route and characterization of olivine nano-silica is presented. The effects of silicate origin and dosage on activator characteristics, reaction kinetics, gel structure and strength are investigated and the CO2 footprint is evaluated. The results show that increasing the activator modulus significantly increases the high crosslink Q contents in the alkali solution, nano-silica based ones exhibit slightly higher percentages of Q3 sites. Nano-silica based mixes exhibit comparable properties regarding the reaction intensity, chemically bound water content and strength. Gel compositions of both nano-silica and waterglass based samples are characterized in detail by using solid 29Si and 27Al MAS NMR. Moreover, replacing commercial waterglass by this alternative silicate source reduces the CO2 emission between 20.4% and 29.0%.