A Promising Mineralization Method of Recycled Hardened Cement Powder and Its Material Evolution Mechanism in Portland Cement

Using recycled hardened cement powder (RHCP) as a substitute for cement clinker presents an opportunity for CO2 reduction and solid waste utilization in the cement industry. This work proposes a promising mineralization method of RHCP to obtain carbonated RHCP (CRHCP), and the mineralization reaction kinetics and corresponding microscopic mechanism of the whole process are analyzed. Results show that by prewetting RHCP before mineralization, the homogeneous liquid film is formed on its surface, which can accelerate the diffusion and dissolution of CO2, making the mineralization reaction rate conform to the ideal diffusion control. Based on this method, the CO2 uptake of CRHCP at the ambient temperature, CO2 concentration of 20%, CO2 partial pressure of 0.1 MPa, w/s of 0.25, and reaction time of 24 h reaches the optimal value of 29.75%, and CRHCP is a core-shell structure of silica gel-coated CaCO3. Moreover, compared with PC, the blended cement system with 20% CRHCP achieves a higher compressive strength, especially the 3 day early strength reaching 36.58 MPa (increased by 20.00%). This is attributed to the positive effect of CaCO3 and amorphous silica gel in CRHCP, resulting in the continuous generation of hydration products and the gradual development of strength in the blended cement system with CRHCP.