Usually consisting of lightweight aggregates, lightweight concrete can also be made using certain types of foaming agents including aluminum powder. This gives the concrete a lower weight and lower density than traditional concrete. Lightweight concrete weighs between 65 and 100 pounds per cubic foot.
For locations where carpet is going to be installed, lightweight concrete is an acceptable material for building a subfloor.
Since lightweight concrete is more prone to cracking than traditional concrete, it can lead to problems when used with hardwood floors. Many manufacturers of hardwood floorboards will not honor warranties if the flooring is installed on a lightweight concrete subfloor. If the hardwood floor is going to be floating, a lightweight concrete subfloor might fare better, but it is still not recommended.