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

An approach for the efficient re-utilisation of waste cement paste powders is proposed, wherein the powders are heated to a certain temperature to prepare regenerated binding materials (RBMs), and then rapidly carbonated by high-concentration carbon dioxide 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 X-ray diffraction analysis, scanning electron microscopy and ²⁹Si nuclear magnetic resonance spectrum, and the compressive strength of the carbonated RBM samples was measured. The results show that the differences in carbonation reactivity, carbonation products of the RBMs and properties of carbonated RBMs can mainly be attributed to the differences in the degree of structural order of newly formed β-dicalcium silicate (C₂S), the content of β-C₂S, free calcium oxide (f-CaO) and incompletely decomposed calcium silicate hydrate (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, 750 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.