About the Effect of Portland Cement Activation on Supersulfated Cements Properties
Résumé
Supersulfated cements (SSC) were first discovered more than hundred years ago, but were abandoned after the 70’s. Nowadays, this technology is experiencing a new boom, due to its durability towards sulfate attacks and to its ultra-low carbon footprint. These cements are composed of ground granulated blast-furnace slag (GGBS), calcium sulfate, and less than 5% Portland clinker (PC) according to the European standard. However, despite numerous studies on this subject, the role of PC content on the hydration of SSCs is still not well controlled and understood. As PC content increases, nonlinear and sometimes pessimum effects are observed for strength development in the short- and long-terms. In this study, the effect of PC content variation is assessed with GGBS from various origins. It is shown that the optimized PC content for strength development is dependent on GGBS chemistry. Slight variations of PC content can lead to either optimum or pessimum of activation. With some GGBS sources, a 0.5%wt. increase of PC could lead to a 50% diminution of compressive strength of SSC at 28 days. Variations of mechanical strength cannot be correlated to hydration heat alone. Water accessible porosity and hydrates formation are also assessed to try to understand these phenomena.
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