How to control the density of foam concrete machine

Foam concrete, also known as cellular lightweight concrete is defined as a cement based slurry, with a minimum of 20% (per volume)foam entrained into the plastic mortar. The density of foam concrete usually varies from 400 kg/m³ to 1600 kg/ m³. The density is normally controlled by substituting fully or part of the fine aggregate with foam. Different application will adopt different density of foam concrete machine, but how to control the density accurately so that it can meet your project?