Effect of foaming gas on the physical and mechanical properties of foamed concrete

Foamed concrete has been widely applied in the construction field due to its excellent thermal insulation performance. Different foaming gases have an impact on the physical and mechanical properties of foamed concrete. Most of the existing research focuses on the regulation of the thermal insulation performance of foamed concrete by foaming gases, but there is still a lack of systematic understanding of the influence mechanism on key physical properties such as its mechanical strength. This study has been carried out to investigate the effect of foaming gas on the physical properties of foamed concrete. Using the physical foaming method, sulfoaluminate cementitious foamed concrete was produced with carbon dioxide (CO₂), nitrogen (N₂), and Air as foaming agents. The resulting foamed concrete samples were tested and analyzed for various physical properties, including water absorption, softening coefficient, compressive strength, tensile strength, thermal conductivity, and porosity characteristics. The results demonstrate that CO₂ foamed concrete (CFC) exhibits superior water resistance, characterized by a lower water absorption rate and a softening coefficient that displays an inverse dependence. Regarding mechanical properties, while CFC possesses enhanced mechanical capabilities, its peak strength is reached later compared to N₂ foamed concrete (NFC) and Air foamed concrete (AFC). In terms of thermal insulation performance, CFC offers improved thermal insulation, and its incorporation of a lower thermal conductivity gas allows for the production of foam concrete with reduced thermal conductivity. Analysis of the stomatal structure and the composition of hydration products indicated a relative scarcity of tandem and deformed pores in CFC, highlighting a finer stomatal structure and an increased presence of calcium carbonate within the hydration products. At an equivalent density level, foamed concrete produced using CO₂ as the foaming agent demonstrates superior water resistance, mechanical properties, and thermal insulation, with the mechanical and thermal insulation properties showing an inverse dependence relationship. Given its advantageous physical properties, along with its potential for carbon sequestration and emissions reduction, CFC presents promising prospects for practical applications.