Overview about the use of Fourier Transform Infrared spectroscopy to study cementitious materials

Fourier-Transform Infrared (FT-IR) spectroscopy shows several advantages that make it interesting to investigate cementitious materials: from clinker or hydrated phases to the bulk or the surface of hardened concrete. The FT-IR analyses in Transmission mode need only a few milligrams of material to provide its composition while other techniques (such as thermo-gravimetric analysis, X-ray diffraction, X-ray fluorescence) need a few grams. Moreover, FT-IR analyses are rapid and give results after a few minutes while other methods need at least a few hours to study one sample. The analyses done in Attenuated Total Reflection mode allow studying the surface of materials without any specific sampling methods (such as cleaning with solvent or storage under vacuum), which can alter the final composition. Clinker and anhydrous cement phases were already studied in 70s to establish the specific peaks of alite, belite and calcium aluminate. The study of major hydrates has been largely performed for the last two decades. FT-IR spectroscopy highlights easily the presence of portlandite (Ca(OH) 2 ), which is detected by a thin unique peak. Moreover, the shift of the peaks assigned to Calcium Silicate Hydrate (C-S-H) can be detected using transmission mode, in order to study the polymerization of the silicates according to the conditions of cure and ageing. AFt and AFm phases (such as ettringite, sulfoaluminate or hemicarbonate) can also be studied using FT-IR spectroscopy. Finally, this method is also able to detect organic demolding agents or CaCO 3 efflorescences at the surface of hardened concrete and can be used to study the interface between the hydrated paste and the polymers or coatings.