Carbon-13 and Oxygen-18 Mass Spectrometry as a Potential Tool for the Study of Carbonate Phases in Concretes

The abundance of carbon‐13 and oxygen‐18 in cement carbonates shows important variations linked to the precipitation process. Three groups of values are observed: (1) the highest values (mean δ13 and δ18= 0 per mil versus PDB and + 30 per mil versus SMOW, PDB and SMOW being the international geochemical isotope standards) are specific of carbonate fillers made from marine sedimentary limestones; (2) the lowest values are linked to direct absorption of atmospheric CO2 by high‐pH cement solutions with important kinetic effects and no isotope equilibration in the high‐pH zone (δ13 and δ18 range from ‐35 per mil to ‐18 per mil versus PDB and +18 per mil to +8 per mil versus SMOW, respectively); and (3) the intermediate group (δ13 and δ18 range from +20 per mil to +30 per mil versus PDB and ‐10 per mil to ‐15 per mil versus SMOW, respectively) is due to precipitation of the mineral‐carbon system dissolved in water. Stable isotope measurements, therefore, may provide information on the proportion and chemical origin of various carbonate generations in concrete.