Assessment of CO₂ effects on the durability of blended cement eco-mortars containing alkaline waste with different carbonation conditions

In exploring ways of achieving climate neutrality by 2050, the cement industry is trialling carbonation of alkaline waste materials for use as supplementary cementitious materials in low-carbon eco-cement manufacture. This paper analyses the durability of mortars with 7 % and 20 % cement replacement by carbonated wastes (CLFS, CBA, CCDW-C) were tested under natural and accelerated carbonation. The mortars were prepared and water-cured for 28 d, then conditioned for carbonation testing in natural and accelerated (3 %) environments. The results show that in mortars containing carbonated waste, natural carbonation depths in outdoor and indoor environments reached 1.5 mm after 90 d, lower than in OPC mortar. Deconvoluted FTIR analyses identified bands (1300–900 cm⁻¹) corresponding to Si–O bonds in the C-S-H gel and the SiO₂-rich gel generated by C-S-H gel decalcification. Under accelerated carbonation, carbonation depths reached 12.3 mm after 70 d. 100-year projection indicates that mortars containing carbonated alkaline waste meet the durability criteria necessary to prevent steel reinforcement depassivation. The findings confirm that prior carbonation makes these materials’ use as SCMs viable since they offer greater reactivity and stability than their non-carbonated counterparts and equal or superior chemical resistance to CO₂.