As in normal concretes the greater the air content the weaker the material, so with foamed concrete densities ranging from 200kg/m3 to 1900kg/m3 it is not surprising that the lower densities produce the lower strengths and at present even the densities at the upper limits do not produce strengths much above 15N/ mm2 . Again as per standard concretes the strength of foamed materials in the main can be attributed to the cement and water content for any given mix, unlike normal concretes however the type of foaming agent used will have a considerable bearing on the final strength, along with, to a certain extent, the type of fine aggregate used.
The cement generally used is ordinary Portland but cement replacements can be used. Ggbs gives the final foamed concrete a cohesive almost sticky consistency which whilst ideal for floor screeds, where a level or fall may be needed, it makes the material unsuitable for the applications such as the abandonment of long sewer runs where fluidity of the foamed concrete is the prime objective. The use of pfa tends to make the material more fluid, but when using high levels of pfa a reaction with certain foaming chemicals can occur resulting in de-stabilization of the mix, causing a breakdown in the air matrix during curing, although this only occurs in very high pfa content mixes and can be combated by using stabilization chemicals.
Propump can offer a full mix design service based on many years of experience both in the field and in the test house.