Micro-Raman spectroscopy applied to depth profiles of carbonates formed in lime mortar

Carbonation takes place in building materials when atmospheric CO2 reacts with Ca2+ present in the pore solution. Of the three crystallized forms of calcium carbonate, calcite is the most thermodynamically stable. Raman spectroscopy is a very useful technique for distinguishing between calcite, aragonite and vaterite. In the present study, micro-Raman techniques are used for the first time to establish the existence of various forms of calcium carbonate at different depths in fully carbonated lime mortar, in trials conducted at a temperature of 20 °C and 75% relative humidity in a chamber with atmospheric CO2. A new model is introduced for samples containing two or three polymorphs. The size of the calcite crystals formed, also determined with this technique, was estimated to be between 25 and 30 μm.