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

Abstract

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.