PERFORMANCES OF SUPER SULFATED CEMENTS
Résumé
Super-sulphated cement (SSC) has been abandoned because of its lack of reactivity. Nevertheless, it could be an alternative to Ordinary Portland Cement in terms of CO2 impact as well as in the field of low pH mortars and concretes. Thus, super-sulphated cement must be re-investigated according to the new European standards. Our initial results on the optimization of the composition and of the curing conditions of such cements are presented herein. Tests are conducted on the basis of normal mortar with two different gauging ratios according to old and new standards for SSC. Four types of curing are used. Mechanical performance is assessed at 2, 7, 28, 60 and 90 days on standard mortar samples (binder/sand mass ratio = 1:3). Tested binders are composed with various amounts of ground granulated blast furnace slag, gypsum or activated gypsum and Portland cement. This study shows that it is completely possible to obtain super-sulphated cement that conforms to the new European standard, with a strength class 32.5N, if the Portland cement content is optimized. For a given SSC formulation, the influence of the origin of the calcium sulphate addition is also pointed out and clearly demonstrates that the development of sulpho-aluminous compounds in these mixtures constitutes a key point in the phenomena of setting and hardening. The use of heat-activated gypsum as a sulphate activator appears preferable.