Portland cement (PC) and steel are primary building materials with increasing demand worldwide. However, their manufacturing processes generate substantial solid waste and CO2 emissions. Steel production yields blast furnace slag (BFS) and steel slag (SS) as unavoidable by-products. The first has been reused as a raw material, but SS has limitations due to the volumetric instability resulting from free CaO and MgO hydration. As an eco-friendly alternative to PC, alkali-activated materials (AAM) have been highlighted for their lower environmental impact, waste utilization and some superior properties compared to PC. Recently, SS has been investigated as potential precursor and aggregate for AAM. Accelerated pre-carbonation is a recent approach to control CO2 emissions that may be also used to mitigate the SS volumetric instability. The literature on the subject is scarce and inconclusive, but some results are promising. This paper analyzes the effect of accelerated pre-carbonation of SS on the mechanical, physical and microstructural properties of AAM mortars using carbonated SS (c-SS) as aggregates. c-SS aggregates were produced by varying the carbonation conditions (temperature and humidity).TGA and FTIR analyses were employed to assess the microstructure changes and the effect of different carbonation conditions on the physical- (density, water absorption), mechanical- (compressive strength) and durability-related (porosity) properties, as well as on the microstructure. The results suggest that the pre-carbonation of SS aggregates may lead to the development of AAM for environmentally advantageous construction products, contributing to innovations in civil construction.