Supersulfated Cement Formulation Using Recycled Gypsum from Building Waste

Among the major environmental issues, the production of cement binders limiting CO2 emissions is a topical issue. This study focuses on the recovery of recycled gypsum, from a building waste sorting center, in the formulation of a supersulfated cement (SSC). The recycled gypsum corresponds to crushed gypsum plasterboard and gypsum precast plaster blocks. The obtained mean size of the gypsum grain is 7 µm. The cellulose content is evaluated to 1.1% and the gypsum content to 81%. The investigated formulations correspond to the coupling of a blast furnace slag (BFS) with a recycled gypsum and a CEM I Portland cement. Several series of binder formulations corresponding to constant BFS content (83.4%) or constant cement content (0.6%) and constant cement/gypsum ratio (9.21) or cement/blast furnace slag ratio (0.72) are considered. The compression performances at 2, 7, 28 and 60 days of mortars realized with the SSC binders are evaluated according to EN-196. The results show the relevance of using recycled gypsum in the manufacture of a SSC. The increase in performances is limited at 2 days (4 MPa) but at 7 days, the compressive strength reaches 60% of the final value. 28-days compressive strength reaches 30 MPa. The evolution of performances after 28 days appears limited. The sensitivity to the content of activators, gypsum and clinker is highlighted. Mechanical performance is mainly governed by the clinker content. An optimum, around 0.5%, of CEM I Portland cement, allows to obtain the best mechanical performances.