Synergistic Reinforcement of Foamed Cementitious Materials Using CO2 Foaming Agent

Abstract

Foamed concrete has been considered a low-strength cementitious material due to its flaky and porous structure. The CO2 foaming agents are thought to enhance the mechanical properties of foamed concrete, but the exact enhancement mechanism is not known. In this study, high-strength foamed concrete was prepared using a CO2 foaming agent, and the mechanism of synergistic reinforcement of foamed concrete with CO2 foaming agent was analyzed using X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), the BET method, and scanning electron microscopy (SEM). The results showed that both sodium bicarbonate and potassium aluminum sulfate helped to generate more ettringite and C-S-H gel. The average diameter of ettringite in Sample FA4 was 5.414 μm. This was about twice the average diameter of ettringite (2.891 μm) in the control group. SEM indicated that this was because calcium carbonate generated in situ by sodium bicarbonate adheres to ettringite crystals and stabilizes ettringite crystal growth. The in-situ generation of calcium carbonate from sodium bicarbonate stabilized the ettringite crystals by attaching them to the ettringite crystals to keep the ettringite crystals from being converted. Incorporating the CO2 foaming agent into the slurry generated large quantities of calcium carbonate and ettringite crystals. Based on the stabilizing effect of calcium carbonate and the strengthening effect of ettringite inorganic skeleton, the interaction between the two can synergistically enhance the foamed concrete matrix. The obtained results lay a theoretical foundation for the synergistic enhancement of foamed concrete by CO2 foaming agent.