Investigation on foam stability of multi-component composite foaming agent

•Multi-component CFA can significantly improve the stability of foam.•High alkaline environment has a negative effect on foam stability.•AAS are suitable to prepare foamed concrete with high foam content.•AAS foamed concrete has better pore distribution than OPC foamed concrete. The multi-component composite foaming agent (CFA) with excellent properties was prepared by sodium α-alkenyl sulfonate (AOS), sodium dodecyl sulfate (K12), coconut oil (CO), and rosin liquid (RL), and three foam stabilizers, namely hydroxypropyl methylcellulose ether (HPMC), xanthan gum and sucrose. The foam stability and the foam stability in an alkaline environment and slurry were studied. The results show that the optimal composition of the multi-component CFA is 0.4% AOS, 0.1 % K12, 0.2% RL, 0.3% CO, 0.08% HPMC, 0.6% xanthan gum and 0.6% sucrose. When the CFA is used to prepare foam, the foaming multiple (FM) is 41, and the 1-hour settlement distance (SD) and the 1-hour bleeding ratio (BR) are zero. Moreover, the foam can maintain excellent stability within 2 h. Under an alkaline environment, when the pH is higher than 12.4, the foam stability will be adversely affected. The effective foam ratio (EFR) of foamed concrete increases first and then decreases with the increase of foam content. When foam content is less than 2.8 L/kg, the foam stability in ordinary Portland cement (OPC) paste is better than that of alkali-activated slag (AAS) paste. When the foam content is higher than 2.8 L/kg, the foam stability of the latter is better than the former. When foam content is 2.8 L/kg, the apparent density OPC and AAS system is 698 kg/m3 and 623 kg/m3, respectively. Compared with OPC foamed concrete, AAS foamed concrete presents more small pores, smaller average pore size and better roundness.