The effects of surfactants on properties of lightweight concrete foam

Lightweight concrete foam is mainly used as a filling for sandwich panels for insulation of buildings. Surfactants are chemical admixtures that play an important role in stabilising the air pores in fresh concrete foam before stiffening. This study investigates the effects of surfactants on the microstructure and pore characteristics of concrete foam analysed by X-ray microtomography. The formation of larger pores due to poor stability of bubbles in the concrete foam is directly related to a substantial reduction of compressive strength. Anionic (negatively charged) surfactants produce a stable aqueous foam. However, in the presence of cement particles, the majority of anionic surfactants adsorb on positively charged sites of cement particles. As the result of considerable migration of surfactants from the air–liquid interface of bubbles, the concrete foam is destabilised. Therefore, a surfactant that can generate a stable foam (with water only) may not be able to generate a stable concrete foam. A combination of an anionic and a non-ionic (neutral) surfactant reduced the maximum pore diameter from 1·84 mm to 1·49 mm and increased strength by 25% compared to the concrete foam stabilised by anionic surfactants alone.