Scientific advances regarding the effect of carbonated alkaline waste materials on pozzolanic reactivity

Using alkaline waste materials as biomass ash (BA), Recycled Concrete Fines (RCF) from constructions and demolition waste (CDW) and ladle furnace slags (LFS), as CO₂ massive sinks worldwide through the generation of new potential SCM by Accelerated Carbonation Technologies to reduce the cement industry's carbon footprint is increasingly attracting attention for its environmental benefits and the materials' improved performance in blended cement matrices. This paper employs characterization and identification techniques (XRF, XRD–Rietveld, SEM/EDX, BET, TG/DTG, FTIR, NMR) to analyse the effect of accelerated carbonation of white ladle furnace slag, siliceous construction and demolition waste and biomass ash on those materials' physical and mineralogical properties, their chemical reactivity and their pozzolan/lime systems' mineralogical phases. The results show that although behaviour differs depending on the carbonated waste materials' alkalinity, all three present notable increases in BET surface area (7–17.5 m²/g) and substantially altered potentially carbonatable mineralogical phases (e.g. portlandite, Ca-olivine, periclase, hydrated cement phases), which mostly transition towards calcite, due to the CO₂ uptake. Thermodynamic modelling of the pozzolanic reaction indicates that CSH/C(A)SH) gels are the most stable phases, followed by ettringite, C₄AH₁₃ and C₄AcH₁₂.