Infrared spectra experimental analyses on alkali-activated fly ash-based binders

Area of Science:

• Materials Science
• Chemistry
• Geology

Background:

• Infrared spectroscopy is crucial for characterizing alkaline activated cements.
• It provides insights into the vibrational modes of chemical bonds in amorphous and crystalline products.
• Understanding these vibrations aids in analyzing the structural evolution during alkaline activation.

Purpose of the Study:

• To investigate the impact of calcium hydroxide (CH) and sodium hydroxide (SH) concentrations, curing temperature, and time on the structure of coal fly ash-based alkaline activated cements.
• To analyze the deconvolution of infrared spectra (4000-400 cm⁻¹) to understand structural changes.
• To correlate spectral variations with the formation of specific cementing gels.

Main Methods:

• Infrared spectroscopy was employed to analyze 9 different mixtures.
• A surface response experimental design was used to vary SH concentration (5.17-10.83 M), CH content (2.93-17.07% ash's wt.), and curing temperature (25, 35, 45 °C).
• Spectra were recorded at 3 and 28 days post-curing, followed by deconvolution of key functional group bands.

Main Results:

• Significant variations were observed in the frequency and area of deconvolved bands for O-H, C-O, and T-O (T: Si, Al) functional groups.
• These spectral changes indicate a reorganization of the network-forming elements from the fly ash and modifiers from CH and SH.
• The formation of calcium-silicate-hydrate (C-(A)-S-H) and sodium-aluminosilicate-hydrate (N-A-S-H) gels was confirmed through characteristic spectral bands.

Conclusions:

• The study demonstrates that CH and SH concentrations, temperature, and curing time significantly influence the structural development of fly ash-based alkaline activated cements.
• Infrared spectral deconvolution effectively characterizes the formation and evolution of C-(A)-S-H and N-A-S-H gels.
• The findings provide valuable insights into optimizing the composition and curing conditions for these advanced cementitious materials.