Semi-dry carbonated recycled concrete paste as alternative to limestone and its reactivity in LC³

Recycled concrete paste (RCP) can be transformed to the carbonated RCP (cRCP) as supplementary cementitious materials (SCM). By blending cRCP with calcined clay prepared from excavated waste, a distinctive limestone calcined clay cement (LC³) was produced. The aim of this research was to assess the reactivity of LC³ produced from the cRCP utilizing different carbonation procedures, via isothermal calorimetry. The carbonation process occurred at 100% R.H. and 20 vol.% CO₂ concentration. To investigate the effect of pre-wetting treatment on the carbonation degree, the RCP was pre-wetted using either deionized water or 0.1 mol L⁻¹ NaOH solution. The carbonation degree and microstructure of cRCP were analyzed using thermogravimetric analysis, X-ray diffraction, and solid-state nuclear magnetic resonance. The results revealed that pre-wetting methods significantly impact carbonation degree, while the alkali solutions had moderate influence. Notably, the pre-wetting procedure aided in decalcifying other hydrates apart from portlandite, leading to compositional variations within the cRCP. Nevertheless, these variations did not significantly affect the cRCP’s reactivity in LC³.