Accelerated carbonation of regenerated binding material prepared with waste cement paste powder

An approach for efficient re-utilization of waste cement paste powders is proposed, that is, the powders are heated to a certain temperature to prepare Regenerated Binding Materials (RBMs), and then rapid carbonated by high concentration CO₂ to prepare high-strength products. The structural evolution during the heating process of waste cement paste powder and the carbonation process of RBMs were investigated by XRD, SEM, and ²⁹Si NMR etc., and the compressive strength of the carbonated RBM samples was measured. The results show that the differences in carbonation reactivity, carbonation products of RBMs, and properties of carbonated RBMs are mainly attributed to the differences in structural order degree of newly formed β-C₂S, the content of β-C₂S, f-CaO and incomplete decomposed C-S-H in RBMs. The strength of the carbonated sample of RBM prepared at 1050 °C was the highest, followed by that prepared at 950 °C, which was significantly higher than those prepared at 650 °C, 750 °C and 850 °C. The content of highly ordered β-C₂S in RBMs with high carbonation reactivity, and the dense stacking of the carbonation products are beneficial for the mechanical properties.