Making Foam Concrete Stronger

Making stronger / better Foam Concrete (FC) is the topic of most Foam Concrete R&D work. So it will be yours if you make FC for whatever reason. Knowing the basics will help a lot in avoiding expensive time consuming mistakes.

Below is an overview of the aspects.

The conclusion I have come to so far is that the following steps and ingredients are a reasonable “beginners guide”.  I left all the references to studies out to make this easier to read. this page is just to give an overview of the topics. If you serious about making FC learn all you can about it. It is possible to make FC with a density of 1200 Kg/m3 and a MPa of 18, but is requires selecting the right ingredients and following a strict procedure.

Foaming agent: must make a stable and small bubble size between 0.5 and 2 mm with the average bubble size distribution over a narrow range around 0.5 mm for the best results.

Foaming machine and method:

The dry method seems to produce “better” foam to make FC.

The machine needs to produce foam of consistent density.

Mixing the foam into the mortar: This need to be done in such a way that the bubbles do not collapse, are evenly distributed, the shape is a “perfect” ball, and are separated from each other.

Adding ingredients to the mortar

So far I have found the following relevant topics

  • Adding Silica fume for a stronger FC
  • Adding Fly-ash for a stronger FC and replacing the cement content
  • Adding super-plasticisers
  • Water cement ratios and MPa relationship
  • adding fibers
  • adding nano-carbon material
  • replacing sand with a non reactive powder

Addition of Fibers

These can be classified in two types, one that reduces the micro cracking during curing and those providing tensile strength when cured.

Adding PE and other synthetic fibers are used to reduce cracking during curing

AR Glass fibers and steel to increase tensile strength.

The addition of fibers can also weaken the tensile strength, if the fiber strength is lower than the FC tensile  strength!

Adding steel fibers is problematic as they sink to the bottom of the FC mix

Focusing on making a good foam to make FC

Use agents that create a foam that does not collapse before the FC is set

Keep the bubble size small, between 0.5 and 2 mm.

Make the average  bubble size distribution as small as possible.

Type of foaming method and equipment used.

Use of Three phase foams can help to make a ‘better” FC

Making the mortar

Use certified Portland cement

Use clean water

Pay attention to the water cement ratio, this is critical!

Use fine sand, sand less than 2 mm, optimum, 0.5 mm gives a better result than coarse sand.

Use additives such as fly-Ash, silica fume, and plasticisers to make FC stronger.


As the curing process is a chemical reaction needing water, do not let your creation dry out. Covering it with plastic / shrink wrap is a common method.

Best to take it out of the mould after 10 to 12 hours, if you use one, and wrap it in plastic for 28 days!

Check the other pages on this site to help you to make a better home

Below is an extract from a book

The Improvement of the Quality of Construction Foam and Non-Autoclave Foam Concrete on Its Basis through the Introduction of Nanosize Additives

By Anastasia Sychova, Larisa Svatovskaya and Maxim Sychov


In order to improve the quality of a construction foam on a protein basis for non-autoclaved foam concrete, a proposal has been made to increase its stability by introducing nanosize additives—SiO2 and Fe(OH)3 sols. It is shown that the effect obtained is connected with various stabilization mechanisms. It is stated that these mechanisms are connected with different energies of chemical bonds formed between the molecules of the foaming agent and the injected sols. By means of electron microscopy, it is stated that the growth of foam stability is connected with an increase in the foam film thickness by one order. An increase in the coefficient of the foam resistance in the cement paste is shown. The stabilization of the construction foam leads to the possibility of using foam concrete hardening accelerators without destroying its structure. The resulting foam concrete is proved to get the increased compressive and bending tensile strength and reduced thermal conductivity and shrinkage in drying. The porosity of the foam concrete obtained is tested by means of mercury porometry. Its phase composition is investigated by X-ray phase and derivatographic analysis.

7. Conclusions

  1. For the first time it is proposed to use SiO2 and Fe(OH)3 sols to stabilize the construction foam on a protein basis in order to obtain high-quality non-autoclaved foam concrete.
  2. It is shown that the stability of the foam stabilized with SiO2 and Fe(OH)3 sols increases up to four times and the coefficient of resistance of the foam in the cement paste increases from 0.9 to 0.98.
  3. The method of IR Fourier spectroscopy shows that the mechanism of the foam stabilization is connected with the formation of various chemical bonds between the molecules of the protein foaming agent and sols: hydrogenous in the case of using SiO2 sol and covalent in the case of Fe(OH)3 sol.
  4. It is established that the new chemical bonds result in the formation of spatial stabilizing complexes in the foam film. This leads to an increase in its thickness by one order, which is confirmed by electron microscopy.
  5. Heat-insulating foam concrete of average density D200 with thermal conductivity coefficient 0.04 W/(m∙°C) was obtained on the basis of the foam stabilized with SiO2 sol.
  6. On the basis of the foam stabilized with SiO2 and Fe(OH)3 sols and NaCl additive, high-quality foam concrete of medium density D400–D600 was obtained. Compressive strength increases up to 50%, tensile strength in bending increases up to 69%, shrinkage in drying decreases by 18%, the coefficient of thermal conductivity decreases by 16%, and frost resistance increases by 20 cycles.
  7. Studies of the porous structure of foam concrete based on the stabilized foam have shown that the specific surface area of the pores increases twice and the average pore diameter decreases from 600 to 520 μm.
  8. Industrial testing of the developed foam concrete of the average density D500 has been made. The use of the foam stabilized with SiO2 sol and the additive of NaCl in its composition allows to reduce the time of cutting strength attainment by 7 hours and to increase the number of products of the first quality category by 23%