Carbon sequestration and mechanical properties of foam concrete based on red mud pre-carbonation and CO2 foam bubbles

This study focuses on the preparation of red mud foam concrete using wet carbonized red mud as a substitute for cement and CO2 foam bubbles. After 56 days of carbonation curing and standard curing, respectively, the carbonation rate, dry density, and compressive strength of the specimen was compared and analyzed under different foam content (20 g, 30 g, 40 g) and pre-carbonation methods. Additionally, CT scanning was employed to model images of red mud foam concrete specimens to analyze changes in air-void diameter and porosity characteristics. At last, the carbon footprint of red mud foam concrete was assessed using a "cradle to gate" approach. The results show that carbonation rate, dry density, and compressive strength of red mud foam concrete are negatively correlated with foam content. Specifically, the carbonation rate of RC20 is 31.92%, the compressive strength is 1.13 MPa, and the dry density is 525.52 kg/m3. Carbonation curing can improve the compressive strength of the specimen, among which the compressive strength of RC30 increases from 0.28 MPa to 0.55 MPa and meets the corresponding strength grade required by relevant standards. The average porosity is positively correlated with the foam content. With the increase in foam content from 20 g to 40 g, the average porosity experiences a rise from 0.632 to 0.843. After carbonation curing, the air-void size distribution range reduces from a range of 150 ∼ 1200μm to 50 ∼ 600μm, air-void size ranging from 50 to 200μm exhibits the highest relative frequency and compressive strength. Furthermore, the RCC30 specimen demonstrates a CO2 emission of 231.32 kg/m3 and a CO2 absorption rate of 35.31 kg/m3, indicating that pre-carbonation has a positive impact on mitigating carbon footprint.