Carbonation curing of alkaline industrial waste for binders: comparison of different wastes

The potential of utilising alkaline industrial waste with weak or no cementitious properties for carbon dioxide (CO₂) capture and for new binders by accelerated carbonation was studied; steel slag (SS), calcium carbide residue (CCR) and waste hydrated cement (WHC) were compared. The carbon dioxide uptake and strength development of SS, CCR and WHC were studied and the relationship of strength development with carbon dioxide uptake and characteristics of carbonation products was analysed. The results indicate that carbon dioxide uptake of SS, CCR and WHC strongly depends on the mineral composition: calcium hydroxide (Ca(OH)₂) and calcium silicate hydrate (C–S–H) show relatively higher carbonation activity; dicalcium silicate (Ca₂SiO₄) absorbs less carbon dioxide than calcium hydroxide and C–S–H. The carbon dioxide uptake of SS, CCR and WHC are 6.1, 23.2 and 17.9%, respectively, after 2 h carbonation curing. Compacted SS, CCR and WHC specimens displayed a compressive strength of 74.9, 20.5 and 28.6 MPa after carbonation for 2 h. Compressive strength development depends on carbon dioxide uptake and mechanical properties of raw materials and carbonation products. Calcium carbonate (CaCO₃) and amorphous products fill the pore structure, making the matrix denser; improvement of pore structure relates positively to carbon dioxide uptake. The highest compressive strength of compacted SS is mainly caused by the high elastic modulus of SS and formation of C–S–H gel in the carbonation process.