Aqueous carbonation of EAF steel slag to produce Supplementary Cementitious Material: Effects on mineral composition, hydration reactivity and mechanical properties

This study investigates the reactivity of Electric Arc Furnace (EAF) slag after direct aqueous carbonation, aiming to identify possible mechanisms to qualify it as a Supplementary Cementitious Material (SCM). To this end, pastes and mortars comprising 10, 20 and 30 % of non-carbonated and carbonated EAF slag were prepared. Compressive strength, isothermal calorimetry, bound water and portlandite consumption tests were performed to ascertain whether the EAF slag can be defined as SCM, and to compare its mechanical and hydraulic properties with those of more conventional SCMs. The CO2 content of the EAF slag after carbonation was 8.6 %. With the R3 calorimetric test, a certain hydraulic reactivity of the as-received and hydrated EAF slag was detected while only a small residual reactivity for the carbonated slag was evidenced. However, the bound water and the portlandite consumption tests suggested a higher reactivity of the carbonated slag. The compressive strength test after 28 days showed that the mortar replaced with 30 % carbonated EAF slag (EAFC-30) developed higher strength than those replaced with 30 % of as-received (EAFAR-30) or hydrated (EAFHY-30) slag. The compressive strength tests at 3, 7 and 28 days showed a retarded hydration of EAFC-30 compared to EAFAR-30. The slow but significant hardening of the EAFC-30 mortars agreed with the previous tests and compared to the behaviour of the EAFAR-30 samples, indicates that pozzolanic reactions were more prevalent after the carbonation. Finally, a comparative analysis of CO2 emissions, substitution percentage and strength class was conducted, confirming carbonated EAF slag as a viable solution.