Effect of nanoparticles and surfactants on properties and microstructures of foam and foamed concrete

The stability of foam is an important factor affecting the stability and strength of foamed concrete. In this study, the foams were prepared by coupling the effects of nanoparticles and surfactants. Multiple methods were employed to investigate the properties and microstructures of various foams and their impacts on properties of foamed concrete. Results reveal that the addition of nanoparticles increased the foam density while decreased the foaming multiplicity, water secretion rate and settling distance, irrespective of surfactant types. Nanoparticles can be combined with the groups of surfactants by electrostatic force, which limits the gas-liquid contact area and the coarsening of bubble and thus stabilizes the foams. Generally, nano-silica (NS) stabilized the foams better than nano-calcium carbonate (NC). Nanoparticle-modified foams reduced the fluidity and increased the viscosity of foamed concrete, and owing to the more irregular and rougher surface, NC had more noticeable effect on fluidity and viscosity than NS. Nanoparticles can change the Ca/Si ratio of pore wall of the foamed concrete and affect the cement hydration, therefore enhancing the strength of foamed concrete to some extent.