Application of Fourier transform infrared spectroscopy in cement Alkali quantification

Abstract

Alkali in cement is responsible for the Alkali–silica-reaction phenomenon that manifests itself in the form of premature cracking in concrete structures such as bridge decks and concrete pavements. X-ray fluorescence spectroscopy (XRF) is commonly used for cement Alkali quantification but a simpler and faster analytical procedure based on Fourier transform infrared spectroscopy (FTIR) has been expanded for this purpose. An analytical absorption band at 750 cm⁻¹ in the FTIR spectra of cement samples belonging to Alkali solid solution of tricalcium aluminate [C₃A(ss)] is used for Alkali quantification. Regression analysis of a plot correlating FTIR absorption band area ratio (750/923 cm⁻¹) to equivalent Alkali Na₂O _e (Na₂O _e  = % Na₂O + 0.658 × % K₂O) measured by XRF shows a linear correlation coefficient, R ², of 0.97. High Alkali cement samples show a higher microstructural disorder coefficient, C _d, which is a reactivity criterion introduced by Bachiorrini and co-authors (Proceedings of the seventh international conference on concrete alkali-aggregate reactions‚ 1986) for ASR-susceptible aggregates. Results of this research indicate applicability of FTIR technique to quantitatively predict cement vulnerability to ASR through the $A_{{750\,{\text{cm}}^{ - 1} }}$ to $A_{{923\,{\text{cm}}^{ - 1} }}$ band area ratio and the magnitude of the disorder coefficient (C _d).