Use of basic oxygen furnace slag fines in the production of cementitious mortars and the effects on mortar expansion

•Basic oxygen furnace (BOF) slag fines used as aggregates are indicative of potentially deleterious expansion.•Replacing cement with BOF slag fines reduces the compressive strength of mortars.•Autoclave expansion of cementitious materials is highly related to mineralogical changes.•BOF slag fines are suitable for the production of alkali-activated slag (AAS) mortars.•AAS mortars produced with BOF slag fines have high volume stability.