Spectroscopic studies of fly ash-based geopolymers

Area of Science:

• Materials Science
• Inorganic Chemistry
• Civil Engineering

Background:

• Geopolymers offer a sustainable alternative to traditional cementitious materials.
• Fly ash, a byproduct of coal combustion, is a key precursor for geopolymer synthesis.
• Understanding the influence of synthesis parameters on geopolymer properties is crucial for their application.

Purpose of the Study:

• To investigate the effect of alkali activator (sodium hydroxide) and water content on the properties of fly-ash based geopolymers.
• To characterize the structural and microstructural changes occurring during geopolymerization.
• To correlate synthesis parameters with compressive strength and apparent density.

Main Methods:

• Fly-ash based geopolymers synthesized with varying SiO2/Na2O molar ratios (3, 4, 5) and water content (30, 40, 50 wt%).
• Characterization using FT-IR spectroscopy, 29Si and 27Al MAS NMR, X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM).
• Compressive strength and apparent density measurements were performed.

Main Results:

• Geopolymers were predominantly amorphous with disordered aluminosilicate phases, and hydroxysodalite was identified as a crystalline product.
• FT-IR analysis indicated geopolymer network formation via SiO(Si,Al) asymmetric stretching vibrations.
• Higher sodium hydroxide content promoted carbonation, evidenced by increased band intensity at 1450 cm-1.

Conclusions:

• Both alkali activator and water content significantly influence the compressive strength and microstructure of fly-ash based geopolymers.
• The study provides insights into the geopolymerization process and the formation of crystalline phases.
• Optimizing synthesis parameters is key to tailoring geopolymer properties for specific applications.