Influence of BaCO3 on hydration of Portland cement

The effect of incorporation of BaCO3 in portland cement hydration has been studied. From this study it is inferred that presence of BaCO3 in cements makes them require a higher quantity of mixing water. However, mechanical resistances do not seem negatively affected,for a formation of carboaluminates by chemical reaction between the barium carbonate and the C(3)A of the clinker appears. The BaCO3 reveals a retardant effect on the setting time, in presence of gypsum as much as in its absence. The BaCO3 with gypsum reacts as BaSO4, a salt of a very high stability. The formation of this barium salt inhibits the formation of ettringite in pastes. Finally, the presence of BaCO3 in cements ensures that no expansive process will occur in sulphatic means either external or internal, for carbonate is going to react with these sulphates and form BaSO4, preventing thus the formation of expansive ettringite.