Everstone foam concrete tests
Typical Properties of Foamed Concrete compiled by the British Cement Association
The mix design for foamed concrete with a dry density of 400 kg/m3 is shown below. This has just under 75% air.
Dry Density (kg/m3) 409
Wet Density (kg/m3) 520
Cement (kg) 314
Dry Sand (kg) 0
Water (kg) 173
Slurry Density (kg/m3) 1784
Foaming Agent (ltr) 0.99
Water (ltr) 33
Foam (ltr) 727
Foamed Concrete – Thermal Insulation
U Values for a thickness of 100 mm
Insert Table 2
To obtain the U value, simply divide the thermal conductivity by the thickness (in metres) that you will be using.
Below is a discussion about calculating mix designs for EVERSTONE Lightweight Foamed Concrete. There are some general comments and then the discussion has been divided into three sections which deal with different ranges of dry densities, they are:
(a) below 700 kg/m3,
(b) above 1200 kg/m3 and
(c) between 700 and 1200 kg/m3.
EVERSTONE Lightweight Foamed Concrete can be made with a range of dry densities, typically from 400 to 1600 kg/m3 (25 to 98 psi), and a range of compressive strengths, 1 to 15 N/mm2 (145 – 2175psi).
In every case when making foamed concrete one has to choose a ratio of sand:cement:water for making the slurry and then calculate the amount of foam that has to be added to that slurry in order to give the correct density of foamed concrete. Table 1 shows some typical mix designs over a range of densities and compressive strengths.
In general terms, the lower the ratio of sand:cement, the stronger the foamed concrete will be. Also foamed concrete of a higher density will also have a higher strength. When placing foamed concrete as a thin section over a large exposed area it needs to be cured in the same way as normal concrete so that it will gain the appropriate strength.
Most mix designs use 0.6 as the water:cement ratio which is standard for ‘normal’ foamed concrete, however it is possible to increase the amount of water to increase flowability. It is also possible to increase flowability by adding extra water after the foamed concrete has been made. Slurry which is too runny is better than slurry which is not runny enough. Cement-only mix designs require slightly less water than those containing sand.
Differences in materials available locally will mean that the results which are obtained will always be slightly different so it is always important to carry out on-site trials
The real key to making good foamed concrete is to experiment with different mix designs. You will then learn what you can and cannot do!
I a) Dry Densities below 700 kg/m3
When making EVERSTONE Lightweight Foamed Concrete with a dry density of less that 700 kg/m3 it is not sensible to include sand in the mix design. The resulting foamed concrete would not have sufficient strength to be of any use. For such light foamed concrete using a ‘cement-only’ mix design is recommended. Hence, Table 1 contains mix designs with ratios of 0:1:0.55 for dry densities of 400 and 600 kg/m3.
Table 1.Mix designs for EVERSTONE Lightweight Foamed Concrete for a range of dry densities. The amounts of cement, sand, water and foam shown for each mix design are required to make 1m3 of EVERSTONE Lightweight Foamed Concrete.
When making foamed concrete we recommend that a density check of the slurry is carried out before the foam is added.
The amounts of foaming agent are for EVERSTONE Foaming Agent, where the foam is made using the dry method using a dilution of 3% and expansion rate of 22 times.
b) Dry Densities above 1200 kg/m3
If the required dry density is greater than 1200 kg/m3 a good starting point mix design is 3:1:0.6 which provides a balance between strength and cost. The ratio of 3:1:0.6 is commonly used as a standard for many applications where a density greater than 1200 kg/m3 is required. If the strength for a given dry density is not high enough the amount of sand can be reduced. This will mean that more cement is being used so the final foamed concrete will be stronger but will also be more expensive.
Table 1 contains mix designs with ratios of both 3:1:0.6 and 2.5:1:0.6 for dry densities of 1200 and 1600 kg/m3.
c) Dry Densities between 700 and 1200 kg/m3
Calculating a mix design to make foamed concrete with a dry density between 700 and 1200 kg/m3 is more tricky. The reason for this is because there is an infinite amount of possible mix designs which will produce foamed concrete with a density in this range. The variety of possible mix designs is large because it is possible to make foamed concrete with or without sand in this range of dry densities. The optimum choice of mix design is the one which will give the required strength for the cheapest cost.
A mix design with a ratio of 3:1:0.6 will give a low strength for densities below 1200 kg/m3. In Table 1 there are mix designs with ratios of both 1:1:0.6 and 0:1:0.55 for dry densities of around 765 and ratios of 1:1:0.6 for dry densities of 1000 kg/m3.