Calcination Characteristics and Performance of Portland Cement Clinker with Hardened Cement Paste

To investigate the influence of hardened cement paste on the calcination and properties of Portland clinker, the calcination characteristics of hardened cement paste at 1000–1450 ℃ were investigated. The effects of hardened cement paste content (i.e., 0%, 10%, 20%, and 30%) and calcination temperature (i.e., 1350, 1400 ℃ and 1450 ℃) on the sintering and properties of Portland cement clinker at the same target values were also studied. The results show that C₃S phase is formed again after the calcination of hardened cement paste at 1300 ℃. For a partial replacement of raw cement material with harden cement paste, the temperature of a liquid phase appears and the apparent activation energy decreases. Its optimal dosage is 20%. The raw cement material with a higher content of harden cement paste can stabilize the crystal formation of C₂S, resulting in a difficulty of C₃S formation. Also, the crystal formation of C₃S changes from R form to M form. The incorporation of an appropriate amount of hardened cement paste (i.e., 20%) improves the mechanical properties of clinker in later stage, which may be related to the difference in C₃S crystal form, C₂S activity and the development quality of cement clinker.