Sustainable development requires alternative possibilities for industrial sector and green binders are feasible solution for construction industry due their environmental impact reduction by valorising waste, reducing energy consumption and the use of natural resources in production process. Steel slag carbon dioxide activated binder is a cement-free construction material which consumes low amount of water and stores CO₂ through its activation. The effect of temperature and CO₂ partial pressure on the carbonation reaction was studied aiming to reach optimal conditions to achieve more desirable mechanical properties for the carbon dioxide activated binder. A Portland cement paste under the achieved optimal carbonation conditions were designed to compare compressive strength and reaction products which were determined by thermogravimetric analysis and scanning electron microscope. An electric arc furnace slag from the national steel industry in Portugal and a Portland cement CP-I were used as binders. This work shows the compressive strength development of a steel slag-based binders under 40, 50, 60 and 70^oC of temperature and 0.5, 1.5 and 2.5 bars of CO₂ partial pressure on the carbonation curing. Portland cement and steel slag binders had similar compressive strength development and reaction products which were mainly calcium carbonates and calcium silicate hydrates. The optimal temperature on the carbonation reaction was 60^oC achieving an average of 97.4 MPa. The partial pressure also showed a strongly influence on the compressive strength development achieve up to 128.1 MPa under 2.5 bars however, the difference between 1.5 and 2.5 bars was not substantial increasing less than 2 MPa in the compressive strength result.