Time, Temperature, and Cationic Dependence of Alkali Activation of Slag: Insights from Fourier Transform Infrared Spectroscopy and Spectral Deconvolution

The use of waste/by-product materials, such as slag or fly ash, activated using alkaline agents to create binding materials for construction applications (in lieu of portland cement) is on the rise. The influence of activation parameters (SiO₂ to Na₂O ratio or M_s of the activator, Na₂O to slag ratio or n, cation type K⁺ or Na⁺) on the process and extent of alkali activation of slag under ambient and elevated temperature curing, evaluated through spectroscopic techniques, is reported in this paper. Fourier transform infrared spectroscopy along with a Fourier self-deconvolution method is used. The major spectral band of interest lies in the wavenumber range of ∼950 cm⁻¹, corresponding to the antisymmetric stretching vibration of Si–O–T (T = Si or Al) bonds. The variation in the spectra with time from 6 h to 28 days is attributed to the incorporation of Al in the gel structure and the enhancement in degree of polymerization of the gel. ²⁹Si nuclear magnetic resonance spectroscopy is used to quantify the Al incorporation with time, which is found to be higher when Na silicate is used as the activator. The Si–O–T bond wavenumbers are also generally lower for the Na silicate activated systems.