Alkaline Activation of Fly Ashes: NMR Study of the Reaction Products

TLDR

The study used 8 M NaOH to activate fly ash, then characterized the resulting reaction products with 29Si and 27Al MAS‑NMR while varying curing time and temperature. NMR revealed that amorphous tecto‑silicates form, with aluminum content decreasing across two phases and the Si/Al ratio of the zeolite precursor rising from 0.95 to 1.86 as curing time extends from 5 h to one week, correlating with changes in cement mechanical properties, texture, and morphology.

Abstract

Reaction products formed during alkaline activation, with 8 M N a OH solutions, of fly ashes have been characterized with 29 Si and 27 Al magic‐angle spinning nuclear magnetic resonance (MASNMR) spectroscopy. In particular, the influence of curing conditions (time and temperature of reaction) has been analyzed. NMR results show the formation of amorphous tecto‐silicates in which the amount of aluminum decreases in the two consecutive formed phases. The Si/Al ratio of zeolite precursor obtained at 85°C changes from 0.95 to 1.86 when curing time is increased from 5 h to 1 week. The evolution of the mechanical properties of prepared cements has also been discussed in terms of the phases formed and texture and morphology of samples.