Effects of carbonation degree of semi-dry carbonated converter steel slag on the performance of blended cement mortar – Reactivity, hydration, and strength

Converter steel slag is the main by-product of steel making process. Around 150–250 million tons of steel slag can be produced in worldwide annually. The high-end application of converter steel slag in cement-based building materials is still facing the challenge due to its poor reactivity. In this study, semi-dry carbonation treatment of converter steel slag powder was investigated to improve the reactivity of slag powder and to sequestrate CO2. The properties of semi-dry carbonated converter steel slags were characterized and the performance of blended cement mortars were evaluated. The results exhibited that the semi-dry carbonation process of converter steel slag was slow, the carbonation degree of it reached 58.95% after 72 h’ treatment. In the pozzolanic reactivity test, the highest calcium hydroxide consumption ratio of carbonated converter steel slag achieved 30% compared to the reference (quartz) with a carbonation degree of 58.95%. However, the pozzolanic reactivity of carbonated converter steel slag cannot reflect the reactivity in blended cement systems. A retardation effect on the hydration process was observed in blended cement pastes with medium (43.76%) and high (58.95%) carbonated converter steel slag powder due to the presence of the high amount of vanadium leached from carbonated converter steel slag particles (10.653 mg/L and 18.831 mg/L). A medium carbonation degree (43.76%) of converter steel slag was observed to induce the largest amount of calcium silicate hydrates and highest compressive strength of cement blends compared to slag powder with low (33.35%) and high (58.95%) carbonation degree.