Which are the foaming agents used in light wt concrete?

I had the same question. They are also called "air entraining agents." They are essentially generic or proprietary industrial detergents marketed under a wide variety of brand names. They are used with a machine called a "foam generator" to introduce tiny bubbles into the concrete mix and maintain the bubbles until it hardens.

I also found that aluminum powder can serve as a foaming agent for concrete, but I don't think that it is commonly used, since that would be a very expensive proposition.