Synergistic effects of Albizia Procera leaf-derived activated carbon and curing regimes on CO₂ sequestration and hardened properties of cementitious systems

This study explores the possibility of using activated carbon (AC) made from Albizia Procera leaves in cement-based materials to improve their CO₂ sequestration capacity and engineering properties. AC was produced through single-step activation–carbonization approach using sodium bicarbonate and by pyrolyzing at 600 °C, resulting in a high surface area of 789 m²/g and a total pore volume of 0.53 cm³/g. Characterization of the AC using XRD, Raman spectroscopy, and FTIR confirmed that the produced AC is mainly amorphous with a turbostratic structure rich in oxygenated functional groups, making it effective for CO₂ adsorption. In order to examine the simultaneous effects of AC and curing regime, cement paste and mortar specimens containing 0 to 3 wt.% of AC were cured under three different conditions: water curing (WC) for 28 days, environmental carbonation curing (ECC; 3% CO₂, 60% RH) for 28 days, and pressurized carbonation curing (PCC; 100% CO₂ under 60 psi) for 24 h followed by 27 days of WC. Tests on the carbonation cured specimens were conducted to study the effect of admixing AC on the CO₂ sequestration capacity of cement paste, densification of microstructure of mortar and its mechanical properties and durability characteristics. XRD and TGA conducted on the paste specimens indicated a higher portlandite consumption and therefore a higher CaCO₃ formation confirming a sharp enhancement of CO₂ sequestration due to addition of AC. SEM images revealed evolution of a denser microstructure of mortar containing AC, especially in PCC specimens, that resulted in a better hardened property of the AC-admixed mortar. Incorporating 3% AC in cement paste and subjecting it to PCC sharply increased the formation of CaCO₃ in cement paste by '12 times compared with (WC) specimen without AC. The same combination of AC dosage and curing regime for the mortar mixture resulted in increased compressive strength by 31%, flexural strength by 67%, modulus of elasticity by 19%, electrical resistivity by 27%, and reduced water absorption by 43%. This indicates a substantial enhancement in CO₂ sequestration of cement paste and significant betterment in mechanical properties and durability characteristics of mortar, when the cementitious systems contained 3% AC and cured using PCC regime.