Abstract: This paper investigated the potential use of basic oxygen furnace steel slag (BOF SS) as a single
aggregate in alkali-activated mortars (AAMs) for building applications. It assesses the influence
of wet-curing and carbonation pre-treatments on the mechanical, microstructural properties
(computerized microtomography and scanning electron microscopy), as well as on the susceptibility
to volumetric expansion (autoclave accelerated test). Untreated BOF SS, natural aggregate,
and a Portland cement (PC) matrix were used for comparison. The results show that the wetcuring
pre-treatment is effective, as it ensures that the AAM mortar with BOF SS aggregate is a
sound building material after accelerated expansion testing. The wet curing of BOF SS aggregate
provides a denser microstructure, less porous interface transition zone (ITZ), and the absence of
microcracks in the mortars, which ensures equivalent mechanical behavior to those mortars made with natural aggregate. In contrary, the carbonated BOF SS aggregate negatively affected the early age strength development of AAMs mortars due to the conversion of the activator into sodium carbonate in AAMs. AAMs and PC mortars with carbonated BOF SS also fail in accelerated expansion tests, like those containing untreated BOF SS
