THIS PAGE IS STILL UNDER CONSTRUCTION, sorry about the mess

The major drawback of FC is the reduced strength, both MPa and ductility.

 Because the FC is made with different densities it is difficult to come to a final conclusion what the “best” FC mix is. The “best” depends on the desired properties. I suggest you read the page Making FC on this website first.

The headings are

Concrete additives

Using Nan-additives

Permeability

Adding Fibers

Water

FC suitable for construction

In this page I concentrate on FC suitable for construction and load bearing structures, and focus on a density of around 1000Kg/m3. To really understand what is happening in the curing process, and what influences the final result, you have to understand the chemistry. I am not going to explain that on this page. In the papers that I recommend for reading to understand the subject in more detail, you find that a lot of the equipment and methodology is only achievable in the lab. Some of the materials and methods are already used in the commercial world, mainly in the pre-fabrication of FC panels and blocks. One example of such a company is http://www.ceentek.com

Before you going to use the more complex and expensive materials, you need to make sure you have the basic mix right for the desired density and materials used. Keep in mind that the W/C ratio is one of the important factors, and different foaming agents and densities require a different W/C ratio for the optimum result. The dilution ratio of the foaming agent can also have an (great) influence on the end result.  Super-plasticisers and other additives have also an influence on the desired/C ratio. It could also be that you may have to adjust the W/C ration once you add nanomaterial to the foam.

I have the idea that if you use a mix design for “normal” high performance concrete, and leave the aggregate out, you have a good starting point.

From reading many papers on FC, I come to the conclusion that varying one mix component can have an influence on other aspects. For example, varying the dilution rate of the foaming agent, can influence the W/C ratio, and so does varying the % of foam in the FC. If you use a super-plasticizer than this also may need adjusting.

Starting point

To be able to compare the qualities, I posted below

Typical properties of normal strength Portland cement concrete:

  • Density – ρ : 2240 – 2400 kg/m3 (140 – 150 lb/ft3
  • Compressive strength : 20 – 40 MPa (3000 – 6000 psi)
  • Flexural strength : 3 – 5 MPa (400 – 700 psi)
  • Tensile strength – σ : 2 – 5 MPa (300 – 700 psi)
  • Modulus of elasticity – E : 14 – 41 GPa (2 – 6 x 106 psi)
  • Permeability : 1 x 10-10 cm/sec
  • Coefficient of thermal expansion – β : 10-5 oC-1 (5.5 x 10-6 oF-1)
  • Drying shrinkage : 4 – 8 x 10-4
  • Drying shrinkage of reinforced concrete : 2 – 3 x 10-4
  • Poisson’s ratio : 0.20 – 0.21
  • Shear strength – τ 6 – 17 MPa
  • Specific heat – c :  0.75 kJ/kg K (0.18 Btu/lboF (kcal/kg oC))

This is copied from:

https://www.engineeringtoolbox.com/concrete-properties-d_1223.html

Some papers talk about ductility:

Ductility can be defined as the “ability of material to undergo large deformations without rupture before failure”. Ductility in concrete is defined by the percentage of steel reinforcement with in it. Mild steel is an example of a ductile material that can be bent and twisted without rupture. I am not sure how exactly this can be compared with Flexural strength. However there standardised tests and the results can be compared.

Compressive strength (MPa)

Every component of FC mix influences the MPa.

If the structure of the FC is close to uniform, by having the same size of sand and air bubbles of 0.5mm or close to it than this is a good start to create a High strength FC

Xxxxx

Mineral admixtures.

Fly-Ash and nano-silica to the mix helps to increase the MPa. The effect of these materials is mainly prescribed to their capacity to fill the spaces between the particles. However the cement content can be reduced by using Fly-Ash without any decreasing effect on the MPA. The following article

Effect of fly ash and silica fume on hardened properties of foam concrete

H. Süleyman Gökçe a,⇑, Daniel Hatungimana b, Kambiz Ramyar

The above is a study on this subject. If you cannot access it, I do have a copy.

Concrete additives

The most common additive is a super-plastisizer, there are many brands on the market, each claiming improvements of the mortar. As there are many different substances on the market all doing “something” I am not elaborating on these as I considered these a “normal” part of the FC mix

Below are a couple of articles I found helpful.

Compatibility of Viscosity Enhancing Agents and

Superplasticizers in Cementitious and Model Systems

Link: https://www.researchgate.net/publication/256680194_Compatibility_of_Viscosity_Enhancing_Agents_and_Superplasticizers_in_Cementitious_and_Model_Systems_Rheology_Bleeding_and_Segregation

Interesting additives for FC are those that reduce the permeability. See heading permeability

Using nano additives

Research in the last 10 years or so has shown that adding nano-carbon, and other nano materials to the mix increases the MPa and the ductility.

There are a number of different ways of doing this; it can be added to the foam or to the mortar. Depending on the type of nano material it can be a real challenge to add this to the mix and have it evenly distributed. The following article is well written and easy to understand.

You may notice that the methods used require laboratory equipment and techniques that are not easily used in the field, but this article covers many materials and methods. Some of them may be successfully used in a commercial application.

Adding nano material to the Foam.

This method has been studied by a number of people and seem to have advantages over adding it to the mortar. Below is a link to a download of the whole article.

https://www.researchgate.net/publication/322924797_Application_of_organic-_and_nanoparticle-modified_foams_in_foamed_concrete_Reinforcement_and_stabilization_mechanisms.

The way the foam is prepared needs some extra equipment such as a high speed mixer and an ultrasonic dispersion machine.

Another study

https://www.researchgate.net/publication/298214083_UHPC_foam_concretes_on_the_basis_of_three-phase-foams

The first paper confirms the findings of the paper above, and has more detail.

Another example of adding nanomaterial and its effects :

https://www.nature.com/articles/srep31654

Research on Oil well cementious mixes is well worth following as they do interesting things and have lots of money to do all sorts of tests and analysis.

Permeability

It appears from the studies below that Fc water ingress phenomena can be compared to that of “normal” mortar.

Now we need to find if the “treatment” and additives used to reduce the water ingress in ‘normal’ mortar also works for FC.

For those who want to have some deeper insight in this subject,

STUDY OF WATER INGRESS INTO FOAMED CONCRETE

LIM BEE YEN (B.Eng. (Hons), NUS)

This is a 177 page theses, well worth reading if you are interested in FC as it also explains other properties related to the water ingress.

I found an abstract of an interesting article

 PERMEABILITY OF FOAMED CONCRETE

C. S. Sanjaya*, National University of Singapore, Singapore

T. Tamilselvan, National University of Singapore, Singapore

T. H. Wee, National University of Singapore, Singapore

32ndConference on OUR WORLD IN CONCRETE & STRUCTURES: 28 – 29 August 2007,

Review: This article debunks the idea that FC is porous! In fact it concludes that: “The foam content of approximately 40% is optimal at which foamed concrete with a very low water permeability of approximately 10-18 to 10-19 m2 can be achieved with the w/cm used in this study. The permeability of mature, good-quality concrete is about 1 x 1 0- 1 0 centimetres per second. However they improved the measuring method, as the usual method had some drawbacks. They propose to make this a standard method for FC. However other researchers have not used this method as far as I know.

I had a link to this but it does not work anymore. Maybe you can find it.

An interesting way of testing for water absorption is done by:

Water transport in foam concrete: Visualization and numerical modeling

She Wei1,*, Zhang Yunsheng1, Miao Changwen1, Hong Jinxiang2, Mu Song2

https://www.icevirtuallibrary.com/doi/abs/10.1680/jmacr.18.00190 If you cannot access this paper trough this link, I have a copy.

Unfortunately this paper does not tell us how much water is absorbed, and what would be an acceptable level. It shows a method of measuring it.

A product that anyone can use is:  Aquron 300  made by www.aquron.com.

 I have been advised that it reduces permeability of FC, but I have not seen any proof on FC with a density of 1000Kg/m3.

Adding fibers

There are many studies done on adding all sorts of fibres to the FC. Some of them trying to use local sources such as coco-palm fiber etc. The use of natural fiber in an alkaline environment need careful consideration for long term performance.

Adding fibers can be divided up into 2 categories. One to reduce the micro-cracking, and one to increase the ductility. Micro crack appear during curing, to reduce this most often polypropylene fibers are added. The effect is that the MPa  is improved. Research indicated that 12 mm long PP fibers are most effective.

To increase the ductility one needs to add fibers that are stronger than the binding forces of the cement. The article below shows the results of adding PP and Carbon fibers with 8 mm length,           7 µ mm diameter and density of 1.7 g/cm3were used.

https://www.researchgate.net/publication/329941278_Toughness_elasticity_and_physical_properties_for_the_evaluation_of_foamed_concrete_reinforced_with_hybrid_fibers

This article shows that adding 1.5% wt of carbon fibers increased the flexural toughness by 36% at 90 days compared to their control mix. No PP fibers were added. Adding these fibers to a FC with a lower density, one could expect a larger % increase in the flexural toughness.

The mix proportions were:

 Cement  500  Sand 1045 water 225 Silica fume  50 foam  1 Kg/M3 and  1.5% wt Carbon fiber.

 The resulting density was 1820Kg/m3.

One of the more interesting papers I found on this subject is:

Compressive and flexural strength of fiber-reinforced foamed concrete:

Effect of fiber content, curing conditions and dry density

Devid Falliano a, Dario De Domenico a,⇑, Giuseppe Ricciardi a, Ernesto Gugliandolo

Their objective was to find a mix that can be used in a 3D printer, but the results can give us a good idea what can be done if we want to use it free form.

Another experiment shows how they achieved making an extrudable FC.

 Rheology of 3D printable lightweight foam concrete incorporating nano-silica

Seung Cho1, Jacques Kruger1, Algurnon van Rooyen1, Stephan Zeranka1, Gideon van Zijl1

1Structural Department, Civil Engineering, Stellenbosch University, South Africa

https://www.researchgate.net/publication/268152022_Effects_of_Fibre_on_Drying_Shrinkage_Compressive_and_Flexural_Strength_of_Lightweight_Foamed_Concrete/link/5462c6ee0cf2c0c6aec1b8d6

This study highlights the limitations of PP fibers in FC

https://www.researchgate.net/publication/268152022_Effects_of_Fibre_on_Drying_Shrinkage_Compressive_and_Flexural_Strength_of_Lightweight_Foamed_Concrete

The present study covers the use of fibre in lightweight foamed concrete (LFC) to produce the lightweight concrete for use in construction of non-load bearing elements. LFC with 600, 1000 and 1400 kg/m3 density were cast and tested. Polypropylene fibres with different percentage were used into LFC and the resulting products were compared to normal LFC. Compressive strength, flexural strength and drying shrinkage tests were carried out to evaluate the mechanical properties up to 180 days. The addition of fibres in LFC showed no contribution on compressive strength but improvement in the flexural and shrinkage test results.

Water

Potable water is always recommended, but not all water is the same.  One study shows why we should potable water for concrete

It makes sense that the water should not contain solids, as the rainwater did in this case.

Below is an interesting paper:

https://www.researchgate.net/publication/329254495_Effect_of_magnetized_water_on_foam_stability_and_compressive_strength_of_foam_concrete

Pdf, Download available.  Sounds a bit far fetched, but this is one of the papers that has a sound basis for their conclusions. The bottom line is that the “water clusters” are broken up. These clusters appear to be bigger than the cement particles. But maybe that is what a super-plastisizer does as well.

I am still looking for papers on the quality of water used in making FC

Email me if you have a question on this topic.

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