Alumino-Silicate Structural Formation during Alkali-Activation of Metakaolin: In-Situ and Ex-Situ ATR-FTIR Studies

Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy was used to demonstrate the reaction mechanisms of alkali-activated materials (AAMs) and the early stage of structure formation in the materials. The effects of different types of alkali activator solutions on the structure formation and reaction mechanisms of AAMs were studied. The results revealed that the main peaks of the ATR-FTIR spectra of the AAMs in the 1300-650 cm(-1) range shifted to a low wavenumber with changing patterns, depending on the activator solution used, indicating that the dissolution and reorientation of metakaolin had occurred. Silica and alumina monomers were dissolved by the NaOH solution to produce crystalline zeolites. Although the reaction between metakaolin and Na2SiO3 solution is slow, the condensation between the Al-OH from metakaolin and the Si-OH from Na2SiO3 solution bonded the chain to be longer. Therefore, the Na2SiO3 solution acted as a template-bonded monomer, formed long chains of Si-O-Si and Si-O-Al, and produced an amorphous AAM structure. In the mixed solution, when the NaOH in it dissolved the Si and Al monomers, the Na2SiO3 in the solution also bonded with monomers and produced a complex structure. The different reaction that metakaolin had with different alkali activator solutions reflected the different phases, microstructures, and mechanical properties of the AAMs produced.

Automated summary

Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy was utilized to investigate the reaction mechanisms and early stage structure formation of alkali-activated materials (AAMs). The impact of different alkali activator solutions on the structure formation and reaction mechanisms of AAMs was examined. The results demonstrated that the ATR-FTIR spectra of AAMs exhibited peak shifts in the range of 1300-650 cm(-1), indicating the dissolution and reorientation of metakaolin, depending on the activator solution used. The different reactions of metakaolin with different alkali activator solutions led to varying phases, microstructures, and mechanical properties of the produced AAMs.