Performance of Blended Cements with Limestone Filler and Illitic Calcined Clay Immediately Exposed to Sulfate Environment

• Autores: Rossetti, Agustín; Ikumi, Tai; Segura, Ignacio; Irassar, Edgardo Fabián
• Año de publicación: 2019
• Idioma: inglés
• Tipo de recurso: documento de conferencia
• Materia: Ingeniería de los Materiales; Illite calcined clay; Limestone filler; Sulfate attack; Curing; Early exposed
• Institución: Comisión de Investigaciones Científicas de la Provincia de Buenos Aires

The use of ternary blended cements with limestone filler and calcined clays can improve the durability of concrete structures exposed to aggressive environ-ments and extend their service life. In sulfate-rich environments, the effects of supple-mentary cementitious materials depend on the replacement level and the progress of hydration. Low level of limestone filler contributes to the stabilization of AFt due to formation of monocarboaluminate. However, high replacement increases the effective w/c ratio and the capillary porosity, favoring the sulfate penetration. The use of active pozzolans improves sulfate resistance by reducing portlandite content and the permea-bility, which minimize ettringite and gypsum formation and sulfate penetration. It is generally assumed that curing prior to sulfate exposure should be extended to allow the pozzolanic reaction to progress. It is currently uncertain the effectiveness of calcined clay in combination with limestone filler when the cement is exposed immediately to aggressive environments. Typical structures affected by sulfate attack are commonly build in situ, thus being exposed to the aggressive environment since casting. This paper analyses external sulfate attack of blended cements with 30 % replacement by combinations of limestone filler and/or calcined clay exposed to Na2SO4 solution at two days after casting. For that, expansions, mass variation, visual appearance and com-pressive strength are monitored in mortars and pastes during 6 months. The evolution of 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.