Making lightweight concrete

Lightweight concrete incorporating expanded polystyrene beads is made by first coating the expanded beads with an aqueous surfactant solution, which preferably contains a substantive cationic surfactant, e.g. a substituted or ethoxylated quaternary ammonium compound containing a C10 to C18 alkyl substituent or an ethoxylated primary or secondary amine having a C10 to C18 alkyl substituent, and a non-ionic surfactant such as an ethoxylated primary or secondary alcohol or a nonylphenol-ethylene oxide condensate. The wet beads are coated with dry cement and then mixed with a further supply of cement, water and sand or aggregate to complete the concrete mix.