Use of Bauxite Residue Slurry as Single Activator in a Hybrid Binder System

The use of bauxite residue (BR) slurry as an activator in a hybrid system is explored in this paper. The strong alkaline nature of the slurry, which is considered as a major barrier for most valorization routes, is beneficial in this approach, where it is used as single source of water and alkalis to activate a hybrid cementitious precursor blend. Moreover, the fineness of the solid fraction of the slurry is expected to improve the particle packing, enabling the reduction of the water content and thus of the final system porosity. Experimentally, ≥ 33 wt% of BR slurry, was homogenized and subsequently mixed with either non-ferrous metallurgy slag or ground granulated blast furnace slag, ≤ 10 wt% of ordinary Portland cement and minor additives. The raw materials were mixed and the resulting pastes were cured at ambient conditions. Satisfactory mechanical properties were reached, exceeding 35 MPa already after 3 d of curing at room temperature. The results are promising, also considering that the slag mix can be potentially replaced by a thermally processed BR, thus leading to a maximization of total BR content in the newly formed binder.