Carbon Dioxide in Hydrated Portland Cement
W. F. Cole and B. Kroone
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A study is made of the wav in which carbon dioxide is held in carbonated samples of portland cement mortar and of calcium silicate hydrate using differential thermal, ther-mogravimetric, and x-ray diffraction methods. The results indicate that the carbon dioxide is chemically bound as calcium carbonate, largely in the form of poorlycrystallized voterite, aragonite, and calcite, and not as a si licate mineral. The carbonate minerals are intimately associated with the siliceous residue that results from the carbonation of the hvdrated cement minerals. They react with this residue when the samples are heated to yield the unstable larnite (@KaO*SiO2) which, at room temperature, is discernible in a rapidly cooled sample. The temperature of the reaction is wel l below that at which well-crystalized calcite and quartz react to produce wollastbnite (CaO*SiO2). Some conclusions are drawn as to the mechanism by which the carbonation of cement minerals could take place.