What is the difference between normal concrete and foamed concrete?

The main differences between normal concrete (also known as dense concrete) and foamed concrete (also known as aircrete, cellular lightweight concrete or CLC) are in the materials used to make them, their physical properties and their end use.

Normal
Concrete
Foamed
Concrete
Stone
Aggregates
Yes No
Foam No Yes
Density 2400
kg/m3
400 - 1800
kg/m3
Compressive Strength > 17 MPa 1 - 15 MPa
Fluidity
(Slump)
Low High
Thermal
Conductivity
0.92 - 1.4
W/mK
0.1 - 0.66
W/mK
A Summary of the main physical differences between normal concrete and foamed concrete

What are they made from?

There are two main differences in the materials that are used to make normal concrete and foamed concrete:

1. The stone aggregates in normal concrete are replaced by foam in foamed concrete. Normal concrete is made from cement, sand, stone aggregates and water, whereas foamed concrete is made of cement, sand, foam and water. For foamed concrete at the lowest densities, sand is not used either.

2. Less water is used in normal concrete. The water:cement (w:c) ratio in normal concrete is typically 0.4, whereas the w:c ratio in foamed concrete is typically 0.6. If the w:c in foamed concrete is too low, some of the foam bubbles will burst causing the foamed concrete to collapse.

  • Foam used to make foamed concrete has a consistency like shaving foam
    Foam for making foamed concrete.
  • The bubble structure of cured foamed concrete
    Cured foamed concrete has a bubble structure.

Differences in Physical Properties

There are several differences in the physical properties of foamed concrete and normal concrete. The most important are density and compressive strength.

Density

Since normal concrete contains stone aggregates it is much heavier than foamed concrete. The density of normal concrete is typically 2400 kg/m3. The density of foamed concrete depends upon how much foam is used in the mix design. Using more foam means the density will be lower. Foamed concrete typically has a dry density between 400 and 1800 kg/m3. The amount of foam used in foamed concrete is deliberately chosen to give the require density and strength for the application that the foamed concrete is being used for.

Compressive Strength

Normal concrete has a much higher compressive strength than foamed concrete does. The compressive strength of normal concrete is 17 MPa or higher, depending upon the mix design and the grade of cement. The compressive strength of foamed concrete is typically from 1.0 - 15 MPa, depending upon how much foam is used, the mix design and the grade of cement. It is possible to make structural strength foamed concrete using additional ingredients. The tensile strength of normal concrete is also higher than the tensile strength of foamed concrete.

Fluidity

In its liquid state foamed concrete is a free flowing liquid. It does not require compaction or vibration when cast into a mould or void. Normal concrete has a lower slump, i.e. it is much less fluid than foamed concrete.

Thermal Conductivity

Foamed Concrete, particularly at the lower end of the density range, has a low thermal conductivity. This makes it suitable for use as thermal insulation on flat dense concrete roofs and for use as pre-cast blocks and panels for walls in buildings.

What are they used for?

Normal concrete is mainly used for structural purposes in building construction and civil engineering, although it has many other uses. It is particularly beneficial where high strength is required.

Foamed concrete is used primarily for void filling, non-structural blocks and panels that are used to build walls, and thermal insulation of flat roofs. Foamed concrete is particularly beneficial for applications that require rapid placement, minimal loading on other parts of the structure and/or thermal insulation. Find out more about applications of foamed concrete.