Enhancing microstructural densification and CO2 sequestration in carbonated mortar using polyethyleneimine functionalized construction and demolition waste fine aggregates

Abstract

This study investigates the effect of polyethyleneimine (PEI) treatment of construction and demolition waste (CDW) fine aggregate on the carbonation behaviour and carbon dioxide (CO₂) sequestration capacity of cement mortar. PEI was applied at dosages of 0.05–0.25 wt% of the CDW fine aggregate. Carbonation depth, pH, XRD, FTIR, TGA, mercury intrusion porosimetry, thermodynamic modelling, SEM–EDS, and compressive strength tests were used to characterize carbonation induced changes. PEI–0.20 was identified as the optimum dosage. The increase in carbonation depth and reduction in pH after 28 days of carbonation indicated greater consumption of alkaline phases and were consistent with enhanced carbonate precipitation. XRD showed a 121.5% increase in total crystalline CaCO 3 , while MIP and SEM–EDS confirmed pore refinement, denser morphology, and Ca-rich carbonate formation. Compressive strength after carbonation increased by 31.3% compared with untreated CDW mortar, reaching 97.7% of the conventional control mortar. CO 2 uptake increased by 335.3%. Beyond the optimum dosage, PEI–0.25 showed reduced crystalline CaCO 3 content, a pH rebound, and lower CO 2 uptake, indicating reduced carbonation efficiency due to limited CO 2 accessibility within the pore network at excessive PEI dosage. PEI-treated CDW fine aggregate thus enables low-carbon mortars combining near-parity mechanical performance with substantially enhanced carbon sequestration.