Effect of barium doping on carbonation behavior of γ-C2S

The gamma polymorph of dicalcium silicate (gamma-C2S) is a potential low-carbon binder owing to its relatively high reactivity with carbon dioxide. This study invstigates the effect of barium (Ba) as a typical impurity on the carbonation characteristics of gamma-C2S. Results on the calcined gamma-C2S powders indicate that Ba doping has little effect on the crystal form of gamma-C2S, but substantially alters its morphology that is characterized by the increasing presence of wrinkles on the surface. Heat evolution during carbonation of the compacted gamma-C2S mortar mixtures shows the suppression of maximum temperature and the delay in reaching the peak in the very early age. This may be associated with the hindering of calcium dissociation as a result of the barium presence. The measured degree of carbonation and compressive strength development of the mortar samples are lower in the early stage but exceed the control in the later stage with a higher barium hydroxide (BH) doping amount. This can be attributed to the reduced thickness of moisture film coating the gamma-C2S particles. This retards the initial carbonation reaction, which may be beneficial for the penetration of CO2 into the sample interior, thus promoting the universal degree of carbonation in the long term. Analysis on the carbonation products reveals aragonite is the preferable metastable calcium carbonate at a low BH doping amount while vaterite is exclusively found as the metastable phase at a high BH amount.