CONICET | Buscador de Institutos y Recursos Humanos

The use of ternary blended cements with limestone filler and calcinedclays can improve the durability of concrete structures exposed to aggressive environments and extend their service life. In sulfate-rich environments, the effects of supplementary cementitious materials depend on the replacement level and the progress ofhydration. Low level of limestone filler contributes to the stabilization of AFt due toformation of monocarboaluminate. However, high replacement increases the effectivew/c ratio and the capillary porosity, favoring the sulfate penetration. The use of activepozzolans improves sulfate resistance by reducing portlandite content and the permeability, which minimize ettringite and gypsum formation and sulfate penetration. It isgenerally assumed that curing prior to sulfate exposure should be extended to allow thepozzolanic reaction to progress. It is currently uncertain the effectiveness of calcinedclay in combination with limestone filler when the cement is exposed immediately toaggressive environments. Typical structures affected by sulfate attack are commonlybuild in situ, thus being exposed to the aggressive environment since casting.This paper analyses external sulfate attack of blended cements with 30 % replacementby combinations of limestone filler and/or calcined clay exposed to Na2SO4 solution attwo days after casting. For that, expansions, mass variation, visual appearance and compressive strength are monitored in mortars and pastes during 6 months. The evolutionof microstructure was evaluated with XRD.Despite the lack of curing prior to sulfate exposure, cement with calcined clay showed an excellent resistance to external sulfate attack, while limestone cements presented a worse performance