Reactions entre granulats calcaires et pate de ciment alumineux

As it has been pointed out about Portland cement, the aluminous cement reactsd with calcite. This reaction has been studied by X-ray diffraction with two types of specimen: the interfacial zone between cement paste and aggregate is investigated with a “double-specimen” model, the contact zone and the bulk are studied with mortars. The hydration reactions of the aluminous cement largely changed in the interfacial zone by the calcareous nature of the aggreagate. Calcite reacts with the two calcium aluminate hydrates CAH₁₀ et C₂AH₈ to form calcium hydrocarboaluminate. This reaction occurs in two steps: firstly C₄A.1/2 \(\bar C\) .12H₂O and secondly C₃A.CaCO₂.11H₂O. As we know, this reaction retards the conversion of the hexagonal aluminates in the cubic form C₃AH₆, which is responsible for damages on aluminous concretes. This retard of the conversion is studied for calcareous and siliceous concretes. The rate of the conversions depends on the nature of the hydrates; it decreases in the following order: C₂AH₈?CAH₁₀?C₃A.CaCO₃.11H₂O The physico-chemical study of the interfacial zone between aggregate and aluminous cement paste is a step in explaining the mechanical comportment of concretes made with aluminous binders.