"There are several ways in which aerated concrete can be manufactured. (a) By the formation of gas by chemical reaction within the mass during liquid or plastic state. (b) By mixing preformed stable foam with the slurry. (c) By using finely powdered metal (usually powder) with the slurry and made to react with the liberated during the hydration process, to give out large quantity of gas. This hydrogen gas when contained in the slurry mix, gives the cellular structure. Powdered may also be added in place of aluminum powder. and bleaching powder have also been used instead of metal powder. But this practice is not widely followed at present."