New insights into the effect of carbonated waste materials on the properties of low-carbon cement pastes

This paper presents the analysis of the influence of previously carbonated alkaline waste materials when employed as pozzolanic additions in eco-cement pastes made with 7 % and 20 % replacement content, one of the cement industry's priority lines of action in its drive to achieve climate neutrality by 2050. The studies conducted focus on three different waste materials: construction and demolition waste (CDW), white ladle furnace slag (LFS) and biomass ash (BA). These are subjected to accelerated carbonation in a static reactor at 100 % CO₂ for 90 min. Solid moisture levels differ according to the nature of the waste material. The results show that CO₂-induced mineralization of these waste materials increases their surface area and chemical reactivity, as demonstrated by calorimetric assay. The primary hydration phases identified in the hydrated pastes are CSH gels, C₄AH₁₃ and C₄AcH₁₂. Furthermore, when compared with the same pastes without carbonated content, the carbonated waste materials present greater compressive strength and greater pore structure refinement. These findings confirm the viability of using this emerging technology to improve cement sector sustainability.