This research paper provides new insights into the impact of accelerated mineralization of alkaline waste materials on the physical and mechanical behavior of low-carbon cement-based mortars. Standardized eco-cement mortars were prepared by replacing Portland cement with 7% and 20% proportions of three alkaline waste materials (white ladle furnace slag, biomass ash, and fine concrete waste fraction) that had been previously carbonated in a static reactor at predefined humidity and CO₂ concentration. The mortars’ physical (total/capillary water absorption, electrical resistivity) and mechanical properties (compressive strength up to 90 d of curing) were analyzed, and their microstructures were examined using mercury intrusion porosimetry and computed tomography. The results reveal that carbonated waste materials generate a greater heat of hydration and have a lower total and capillary water absorption capacity, while the electrical resistivity and compressive strength tests generally indicate that they behave similarly to mortars not containing carbonated minerals. Mercury intrusion porosimetry (microporosity) indicates an increase in total porosity, with no clear refinement versus non-carbonated materials, while computed tomography (macroporosity) reveals a refinement of the pore structure with a significant reduction in the number of larger pores (>0.09 mm³) and intermediate pores (0.001–0.09 mm³) when carbonated residues are incorporated that varies depending on waste material. The construction and demolition waste (CCDW-C) introduced the best physical and mechanical behavior. These studies confirm the possibility of recycling carbonated waste materials as low-carbon supplementary cementitious materials (SCMs).

Using CO₂-mineralised alkaline waste as a supplementary cementitious material has the potential to advance sustainable construction practices. This paper evaluates the effect of carbonating three fine industrial waste materials—construction and demolition waste, ladle furnace slag, and biomass ash—on the durability performance of blended cements in which they replace 7% and 20% of ordinary Portland cement. The performance of carbonated waste was compared with that of their non-carbonated counterparts through chloride ingress resistance, a key parameter governing reinforcement corrosion. The results show that prior carbonation can significantly influence chloride transport properties, although the magnitude and direction of the effect depend strongly on the waste type and replacement level. Mortars with carbonated construction and demolition waste or ladle furnace slag generally reduced the chloride diffusion coefficient compared with the corresponding non-carbonated materials. This behaviour was associated with greater portlandite consumption and enhanced chloride-binding capacity. Nevertheless, none of the blended systems outperformed the ordinary Portland cement (OPC ) in terms of chloride diffusion resistance. Conversely, biomass ash at 20% replacement led to markedly reduced performance, with the estimated time to steel depassivation decreasing to 1–2 years under the exposure conditions considered. These findings indicate that prior carbonation may improve the suitability of some wastes for cementitious applications relative to their non-carbonated counterparts, although the resulting chloride resistance remains lower than that of OPC. The benefits are of waste carbonation are therefore material-dependent and should be assessed on a case-by-case basis.