A novel insight into CO2-cured cement modified by ultrasonic carbonated waste incineration fly ash: Mechanical properties, carbon sequestration, and heavy metals immobilization

As a typical alkaline hazardous waste, municipal solid waste incineration fly ash is used for CO2 storage and cement supplementary material, contributing to carbon emission reduction and hazardous waste management. This study proposed a new idea of using ultrasonic accelerated carbonated fly ash (UFA) to modify CO2 mineralization cured cement, aimed at recycling FA while enhancing cement performance. Incorporating small amounts of UFA (5% and 10%) significantly improved the mechanical properties of cement paste, with the optimal inclusion of 10% UFA yielding a compressive strength of 50.23 MPa—higher than that of pure cement (41.04 MPa). The UFA contributed to pore filling and acts as a nucleation site for CO2 mineralization, forming stable flaky calcite and thus enhancing the microstructure. Conversely, higher UFA contents (20% and 50%) reduced performance due to a dilution effect that impaired the hydration product structure. Kinetic analysis via the Avrami-Erofeev model revealed that CO2 diffusion and crystal growth primarily control the mineralization reaction. The 50%UFA cement paste exhibited the greatest carbon fixation depth, with a carbon sequestration capacity of 186 g-CO2/kg-PC. This was attributed to its enhanced porosity and pore size, which facilitated CO2 diffusion. The 10%UFA cement paste, which had the highest compressive strength, also achieved a carbon sequestration capacity of 158 g-CO2/kg-PC, surpassing the 144 g-CO2/kg-PC of the pure cement paste. Moreover, the proposed UFA-modified CO2 mineralization cement displayed a low risk of heavy metal leaching under alkaline or acidic environment. [Display omitted]