Foam concrete

Foam concrete is a cement-based slurry with a minimum of 20% (by volume) foam, entrained into the plastic mortar and is a lightweight cellular concrete (LCC) or low density cellular concrete (LDCC), also known a cellular lightweight concrete or reduced density concrete, foamed concrete, foamcrete, and aircrete. As no coarse aggregate is typically used, it is formally a mortar, not a concrete, and may be called "foamed cement" as well. Density typically varies from 400 to 1600 kg/m3. The density is normally controlled by fully or partially substituting the fine aggregates with foam.

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Characteristics of Lightweight Concrete (28 Sept 2020)

Based on a Synthetic Polymer Foaming Agent by Marta Kadela, Alfred Kukiełka, Marcin Małek, Materials (Basel). 2020 Nov; 13(21): 4979. PMCID: PMC7663941; Published online 2020 Nov 5. doi: 10.3390/ma13214979 PMID: 33167446

This study aims to assess the properties of foamed concrete with a density of around 500, 700, 800 and 1000 kg/m³ formed by using a synthetic polymer-based foaming agent. The distribution of pores, wet and dry density and compressive strengths were evaluated. In addition, the creep deformations... were measured.

Foamed concrete with higher densities (700 and 800 kg/m³) showed similar characteristics of pores, which were different from those of samples with a density of 500 kg/m³.

Compressive strength equal to 5.9... 5.1... 3.8... and 1.4... MPa was obtained for foamed concrete with a density of [1000, 800, 700 and 500] kg/m3, respectively. The obtained compressive strengths were higher than those found in the literature...

Due to sustainable development and the related reduction in energy consumption and CO2 emission... lightweight concrete, aerated concrete and foamed concrete are increasingly used...

Foamed concrete (FC) is classified as lightweight concrete with a density ranging from 280 to 1800 kg/m³... and with a minimum of 20% of air pore volume in the cementitious mix...

Foamed concrete was made using the pre-foaming method with physical foaming or mixing and the foaming method with chemical foaming...

Foamed concrete is characterized by its ability to flow, self-compact and self-level as well excellent thermal and acoustic insulation...

The compressive strength ranges from 0.21 to 10.34 MPa for a density of 300 to 1600 kg/m³ ...[in] typical application.

Amran et al... Fadila et al... Kang... Fernando et al... and Portal et al... produced foamed concrete for use in wall panels. Rum et al... used foamed concrete as a component in a profiled composite slab. Kadela et al.., Drusa et al.., Tian et al... and Lee at al... used foamed concrete in a pavement or floor structure to transmit a load on a subsoil, including weak soil. Moreover, foamed concrete has been used in building foundations...

[F]oamed concrete has the potential to become a mainstream material that uses waste material successfully as a replacement for cement or fine aggregate...

The components of foamed concrete (type of cement... water... water/binder ratio... additives... and admixtures...) have a significant effect on its properties...

Even foamed concrete with a compressive strength of 70 MPa can be made by the addition of polypropylene fiber and fine silica fume and used in high-performance cement...
- Ref: Performance properties of structural fibred-foamed concrete Amran et. al., Results in Engineering Vol. 5 (Mar 2020) 100092. doi: 10.1016/j.rineng.2019.100092.

Fibre-Reinforced Foamed Concretes: A Review (28 Sep 2020)

Mugahed Amran, Roman Fediuk, Nikolai Vatin, Yeong Huei Lee, Gunasekaran Murali, Togay Ozbakkaloglu, Sergey Klyuev and Hisham Alabduljabber (Sep 28, 2020) Materials 2020, 13(19), 4323; source.

Foamed concrete (FC) is a high-quality building material with densities from 300 to 1850 kg/m³, which can have potential use in civil engineering, both as insulation from heat and sound, and for load-bearing structures. However, due to the nature of the cement material and its high porosity, FC is very weak in withstanding tensile loads; therefore, it often cracks in a plastic state, during shrinkage while drying, and also in a solid state.

Several factors... affect the mechanical properties of FRFC, namely: fresh and hardened densities, particle size distribution, percentage of pozzolanic material... and volume of chemical foam agent. ...rheological properties ...are influenced by the properties of both fibres and foam; therefore, it is necessary to apply an additional dosage of a foam agent to enhance the adhesion and cohesion between the foam agent and the cementitious filler in comparison with materials without fibres.

Various types of fibres allow the reduction of... autogenous shrinkage [by] a factor of 1.2–1.8 and drying shrinkage by a factor of 1.3–1.8.

Incorporation of fibres leads to only a slight increase in the compressive strength of foamed concrete; however, it can significantly improve the flexural strength (up to 4 times), tensile strength (up to 3 times) and impact strength (up to 6 times).

[T]he addition of fibres leads to practically no change in the heat and sound insulation characteristics of foamed concrete...

FRFC... has applications in various areas of construction, both in the construction of load-bearing and enclosing structures.

Foamed concrete (FC) has recently become widespread building material for thermal insulation and structural purposes...

At its core, FC is made from a concrete mixture into which pre-prepared foam is introduced, creating a system of closed voids within the hardened composite...

FC, which is one of the varieties of cellular concrete[,] attracts... builders worldwide... has nice workability... can be used for thermal and sound isolation, flame protection as well as blast viscosity; nevertheless, low mechanical and physical characteristics... limit the scope of its application in concrete structures.

[A]ttributable to a large amount of entrained air, the hardening mixture is subject to shrinkage to a large extent.

The utilization of different fibres... reduce[s] shrinkage cracks and improve[s] mechanical properties, particularly tensile and flexural...

FC... reduces construction expenses and allows for sustainable designs with low weight...

To increase the target compressive strength at least up to 25 MPa [3,626 psi], engineers have applied various modern approaches... In the making of high strength [cement], low water to binder ratio (w/b) and the inclusion of fly ash, silica fume, and ultrafine silica powder are recommended as a substitute to sand...

To increase FC’s mechanical characteristics, the water-binding ratio w/b is usually maximally reduced, as well as the use of finely dispersed pozzolanic raw materials as a replacement for fine aggregate...

Incorporation of randomly oriented fibres into foamed concrete can improve load transfer in different directions, and tensile strength increases due to the creation of an elastoplastic composite... in load-bearing structures...

Considering that fibreglass also increases mechanical strength, this is an important factor in FC’s stability... High-strength foamed concrete is obtained by introducing polypropylene (PP) fibre into the raw mix... Many of the currently used fibres have been investigated, including PP... blend of polypropylene with glass... cellulose... kenaf... steel... palm oil, coconut... and other fibres... introduced in an amount of 0.2–1.5% volume of the concrete mixture; however, in this article, the fibre content ranges upper limit has been extended to 5%. As an alternative to traditional reinforcement, one strategy with composite mesh and mesh combined with fibre has also been studied for lightweight foamed concrete (LWFC)...

Using synthetic and natural fibres (glass and carbon ones) in FRFC has shown excellent durability properties with reduced drying shrinkage, high modulus of elasticity and increased mechanical strength...

Except for some papers... the developed FRFC has a 28-day tensile and compressive strength not even more than 2.5 MPa and 50 MPa, respectively.

[T]he use of fibres (e.g., synthetic, metallic and natural fibres) as reinforcement is reported as an effcient material added into the fibre-reinforced FC (FRFC) matrix... to bridge the cracks... [reduce] shrinkage crack[s], to enhance load transfer and to improve the hardened properties by altering the characteristic brittle behavior [in]to elastic–plastic behavior, particularly, the flexural and tensile properties.

The fibre matrix interface and matrix densification can deliver a greater load carrying capacity of FC reliant on the toughness of the fibres. The FRFC prolongs post-crack ductility even... [with] repeating loading cycles.

This paper reviews the production of FC, type of foam agents, method of foaming generation, type of fibres used and factors affecting the mechanical properties of FRFC. [It also provides] a critical review on the properties and behaviors of FRFC as well as... research development trends to generate... insights into the potential applications of FRFC as suitable concrete materials... robust FRFC composites, for modern buildings and civil engineering applications... to draw a more complete picture of the current state-of-the-art.

Axel Erikson was the first to patent Portland cement-based FC technology in the year 1923... The characteristics, behaviour and structural applications of FC have been widely investigated...

FC is reportedly proved to be superior to conventional concrete mainly due to its lower density, which helps in reducing the static construction loads, foundation volume, labour, transportation, and exploitation expenses...

Many countries like the United Kingdom, Germany, Philippines, Turkey, and Thailand have made the use of FC in many construction applications...

The bubbles’ volume varies from 6% to 35% of the total final mixture in most of FC applications...

Foam agents are inorganic and organic compounds... in pellet or powder foam. Organic agents are azodicarbonamide, hydrazocarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylene tetramine, toluenesulfonyl hydrazide, benzene sulfonyl hydrazide, azobisisobutyronitrile and barium azodicarboxylate. While inorganic agents are NaHCO₃, NH₄HCO₃, (NH₄)₂CO₃, and Ca(N₃)₂... Polyurethane foams are used as insulation spray for air-sealing buildings. Foam stabilizer is added to enhance its slurry viscosity which consists of 20% of triethanolamine 40% of polyacrylamide and 40% of hydroxypropyl methyl cellulose... [T]he various foam agents are available in E-markets worldwide.
- Note: Table 1 lists following foam agents: Genfil: high-yield Herbal resin based foam agent Stable foam; LithoFoam: highly active Protein based, improved silicone oil resistance, frost resistance; CMX^TM: Synthetic based, performs well with a wide variety of ad-mixtures, proven to withstand higher lifts; Sakshi CLC: Synthetic based, air entrainers, set accelerator, water reducer; EABASSOC: Synthetic based, highly concentrated, highly efficient liquid; VariMax: Synthetic based, a variable high dilution ratio; LITEBUILT: Synthetic based, fast turnaround in production process, no harmful or toxic fumes.

The chemical foamer is ordinarily protein-based, hydrolysed protein, detergents, synthetic, saponin, soaps of resin, and glue resins... The protein foamers form in a more grounded and enclosed cell of air-void structure, which allows the incorporation of a more prominent volume of bubble and gives a higher steady bubble network. In contrast, the synthetic ones abdicate more prominent extension and hence lower density... [T]he extreme use of chemical foam volume causes a decrease in flow, density and mechanical properties of FC... However, FC’s flow is considerably influenced by the time of mixing, showing that the lengthy mixing can result in the damage of the enclosed cell of air-voids by plummeting the air content...

Reportedly, FC’s mechanical properties are commonly dependent on the volume of foam content instead of its dependence over the proportion of water and cement...
- Ref: Welker, C.D.; Welker, M.A.; Welker, M.F.; Justman, M.A.; Hendricksen, R.S. Foamed Concrete Compositional Process. U.S. Patent 6,153,005, 28 November 2000.

Fibre-reinforced concrete (FRC) is one containing fibrous material that improves its structural solidity...

Basalt fibre is cut from a continuous basalt fibre with a diameter of 17 μm, 2.5 times superior in tensile strength to superior steel. Average fibre length: 6 to 24 mm. Recommendations for the dosage of basalt fibre: 1 kilogram per 1 cubic meter of mortar or concrete. It is necessary to introduce it into the mix with water, after stirring the fibre until it is evenly distributed in the water, it is necessary to slightly increase the mixing time (up to 5–10 min) for uniform distribution in volume.

For fibreglass concrete, an alkali-resistant (AR) fibre should be used.

PVA fibres have a higher tensile strength [1300 MPa] than [other] synthetic[s] and are relatively economical... Due to its low density... the fibre is ideal for foamed concrete... the elastic modulus is 25 GPa...

[P]olypropylene fibre, despite the low modulus of elasticity (1.5–10 GPa), has relatively high durability... an even lower density than PVA... [and is] ideal for foam concrete. The... tensile strength is 240–760 MPa and the ultimate elongation is 15–80%...

[F]ibres content should be controlled within 5% to achieve optimum concrete behaviour where excessive fibres may reduce the concrete strength.

As claimed by Lim et al... finer... aggregate size may increase the strength of FC... As the particle size grading decreased, from passing through 2.36 mm sieve to 0.60 mm and 0.10 mm sieve, the strength has an increasing trend... With finer aggregate, the workability also increases and reduces the use of compaction that potentially bursts the bubble inside concrete paste.
- Ref: Lim, S.K.; Tan, C.S.; Chen, K.P.; Lee, M.L.; Lee, W.P. Effect of different sand grading on strength properties of cement grout. Constr. Build. Mater. 2013, 38, 348–355.

Silica fume has been found to benefit concrete properties [145], especially compressive strength and durability. It was added to FRFC and was found to have a 25% increment, at most, in compressive strength...

With the same quantity of addition, fly ash and metakaolin specimens have higher compressive strength than silica fume... [N]ano-silica also have been investigated... The 4% nano-silica was found to have more excellent mechanical properties, durability and microstructure than plain FC and 15% silica fume... Silica fume was eFFectively enhanced the flexural, compressive and tensile strength and durability with a combination of waste marble material... [T]o enhance LWFC properties, apart from traditional materials, such as FA or SF... the recycled components like the slag of various types... or glass... have also been included in the LWFC concrete matrix... [T]he pozzolans may increase the concrete strength and its durability...

FC is obtained from mixing base mix (normally mortar) with preformed foam (diluted foam agent with high pressure). ...FC consists of cement as binders, sand as aggregates, water, and foams. As a consideration of economic and performance enhancements, many researchers... [introduced] additives or replacements to the FC, such as fly ash... silica fume... superplasticizer... fibres, and others. There is no specific method to determine the mixing proportions. However, Kearley... proposed the calculation of mixing the proportions by the target density method, and other researchers have practiced this.
- Ref: Kearsley, E.P.; Wainwright, P.J. The effect of high fly ash content on the compressive strength of foamed concrete. Cem. Concr. Res. 2001, 31, 105–112.

Fibre-reinforced foam concrete mixture is poured into molds without mechanical compaction, so it must have self-sealing rheology.

For optimization various performances such as consistency, rheology and workability, segregation and bleeding should be considered... These parameters mainly depend on the water/cement ratio, supplementary cementitious materials, aggregates, superplasticizers, foam agents, and the type and concentration of fibre.

[T]he mixture’s components must be precisely calculated to improve the rheology and consistency of FRFCC, attain self-sealing behaviors, and enhance the adhesion and cohesion between the foaming agent and the cementitious filler. One of the main features influencing the rheology and texture of fresh FRFCC is the mixture’s water content. Another main factor is the fibre density... the adding of light fibre negatively influences the constancy of the mixture. Besides, the rheology of FRFC worsens with excess foam due to the higher air volume, while the incorporation of SP improved the flow rate. ...[T]he "Portland cement—silica-containing additive-complex modifiers" system can significantly reduce shear stress and create easily compacted fibre-reinforced foamed concrete mixtures.

The introduction of fibre somewhat reduces workability. The fibres large specific surface absorbs more of the cementitious mortar around the fibres and, consequently, increases the viscosity of concrete, which contributes to a slight reduction in... spreadability. However, with proper FRFC mix... improvement in workability can be achieved by introducing the optimum fibre amount.

The principle of the segregation and bleeding (water separation) test is that after sampling, the concrete mixture is left for 15 min... After that, the upper part of the sample is poured onto a sieve with a mesh size of 5 mm. After two minutes... [t]he stratification coefficient is calculated as the mixture ratio above the sieve to [that below it].

[S]uperplasticizers, if used to reduce w/c, do not cause separation or water separation. The use of a clogging micro filler (for example, finely ground limestone or quartz sand) helps to reduce... water separation... [T]he micro filler [may create] an additional "stability framework," which increases... resistance to segregation...

[I]nclusion of fibres [having] more than one type or more than one size... [has been] recognized as hybrid fibres.

[C]ompressive strength decreases exponentially when concrete’s density decreases... FC’s compressive strength commonly decreases gradually as the entrapped bubbles increased; however, its strength may be enhanced by adding fibres... [F]ibres can enhance its hardened [physical] properties (including... toughness and elasticity)...

[O]verall strengths were mainly influenced by the factor of combined water/cement and air/cement ratio...
- Ref: Awang, H.; Mydin, A.O.; Ahmad, M.H. Mechanical and Durability Properties of Fibre Lightweight Foamed Concrete. Aust. J. Basic Appl. Sci. 2013, 7, 14–21.

Performance properties of structural fibred-foamed concrete (Mar 2020)

by Amran Y.H.M., Alyousef R., Alabduljabbar H., Khudhair M.H.R., Hejazi F., Alaskar A., Alrshoudi A., Siddika A. Results in Engineering Vol. 5 (Mar 2020) 100092. doi: 10.1016/j.rineng.2019.100092.

The objective of this study is to develop structural fibered foamed concrete by the addition of polypropylene fiber, fly ash, and silica fume. Foamed concrete was obtained by replacing sand with fly ash. The properties of the foamed concrete were enhanced with polypropylene fiber and fine silica fume.

Structural fibered foamed concrete with dissimilar densities of foamed concrete (1000, 1300, 1600, and 1900 kg/m³) [62, 81, 100, 119 lb/ft³] is essential for examining compressive, flexural and splitting tensile strengths, drying shrinkage and creep.

Fine silica fume and polypropylene fiber considerably promoted the hardened strength... [P]olypropylene fiber significantly enhanced the tensile strength and increased the creep resistance and drying shrinkage.

[S]tructural fibered foamed concrete can be used as a substitute lightweight concrete material for the production of structural concrete applications... today.

The neat cement with fine sand was used in the fabrication of a lightweight FC with uniformly distributed micro- or macroscopic discrete air cells...

FC provides unique advantages, such as thermal and acoustic insulation and resistance to fire and termite attack, lowers cost in construction, and produces... eco-friendly structures...

Generally, FC is designed to achieve a low compressive strength around 1–10 MPa [150 to 1,500 psi] and can be applicable in filling voids and restoring trenches but cannot be used in the construction of any structural member... To achieve the desired strength of at least 25 MPa [3,600 psi]... different innovative solutions... are economically and environmentally admissible...

[S]mall water-to-binder (w/b) ratio and the inclusion of silica fume (SF), ultrafine powder of silica and fly ash (FA) as an alternative of sand is recommended in the production of high-strengths FC...

A number of studies produced FC with compressive strength of around 50 MPa [7,300 psi] by applying special curing condition and described the relationships among strength, density, and porosity...

The present paper attempts to develop structural fibered foamed concrete (SFFC) with 10–70 MPa [1,500-7,300 psi] compressive strength and 1000–1900 kg/m³ [62-119 lb/ft³] density.

Ordinary Portland cement (OPC)... was used to prepare the specimens... Dry and un-compacted SF with a SiO₂ content of 91.9% was used... A residue of approximately 1.56% was obtained after sieving the residue through a 45 Am sieve. ...Class F FA was used in accordance with ASTM C 618... PP fiber with a 100 μm (dia.) and 10 mm (length) was used... A [protein-based] foam agent... with an aerated density of 80 kg/m³... after diluting... [with] water... in a ratio of 1∶40 [by volume] was used... A naphthalene-based super-plasticizer was applied... The dosage of the super-plasticizer and the flow of premix paste were low... [A] cohesive state was observed in the final FC mixture, in which the cementitious particle appeared... wrapped by the foam. ...[O]nly one type of middle-east sand [Fineness modulus 1.72] was used... spherical and smooth-surfaced...

Practically, a sufficient flow range in a premixed paste is a proof of the effective production of FC. When the value of flow seen was lesser than the limit, the mixes of the developed premixed paste and foam was considered in-cohesive. The binders seemed to be covered by air bubbles, which collapsed afterwards. [W]hen the value of flow was greater than the limit, seclusion happened and foam bubbles inclined to collapse.

[A]fter 7 days of curing, the concrete without SF attained approximately 65%–80% of [compressive] strength at 28-day[s]... the specimens encompassing SF gained approximately 80%–95%... [I]n FC without SF, the 90-day strength was approximately 75%–90% of the conforming... strength. [S]pecimens encompassing SF gained around 80%–95% of the equivalent 90-day strength. Therefore, the FC with FA can gain strength over a long period.

[L]ightweight FC material can develop strength of equal to 60 MPa [8,700 psi] with a density of approximately 60%–70% of the traditional concrete density.

For a specified volume of foam, the PP fiber significantly improved the hardened strength. ...This advantage was also observed in the FC specimens with SF. Nevertheless... addition of PP fiber condensed the flowability of mix. Thus, we increased superplasticizer dosage... 0.8% fiber content was the best... level on the basis of a swap between performance enhancement and flowability loss.

Foam Concrete (26 Mar 2020)

: A State-of-the-Art and State-of-the-Practice Review by Yanbin Fu, Xiuling Wang, Lixin Wang, and Yunpeng Li, Hindawi Advances in Materials Science and Engineering, Volume 2020, Article ID 6153602, source.

FC is a type of cement mortar containing cement, water, and stable and homogeneous foam introduced using a suitable foaming agent... regarded as self-compacting materials...

Other academic terms describing this material are lightweight cellular concrete, low-density foam concrete, or cellular lightweight concrete, etc...

The textural surface and microstructural cells make it widely used in the fields of the thermal insulation... sound absorbance... and fire resistance...

A great number of environmentally friendly buildings using FC as nonstructural members have been built in recent years... It is also used for bridge abutment filling to eliminate differential settlement... In addition, the applications for prefabricated components production... building foundation... and airport buffer system are also reported...

Foam concrete has been commonly used in construction applications in different countries such as Germany, USA, Brazil, UK, and Canada...

This material has renewed interests in terms of underground engineering. This is the requirement of underground structure to control the overlying dead load... whereas the controllable density and low self-weight... could be effectively used for reducing the dead load. Other properties, such as seismic resistance, ideal coordinated deformation capacity, and easy pumping...enhance the popularity of this material...

FC has been quickly promoted as construction materials for tunnels and underground works. Its excellent self-flowing capacity can be used to fill voids, sink holes, disused sewage pipes, abandoned subways, and so on. The low and controlled self-weight makes it capable for load reduction or liner elements in tunnel and metro systems...

Tan et al.... performed an investigation on compression deformation properties of FC used as liner element for the purpose of further explaining stress and strain response. The experimental results indicated that the compressive strength of FC increases with density and confining pressure, whereas the modulus of elasticity has a positive correlation only with densities regardless of confining pressure. And no notable correlation was observed between peak strain and density, but peak strain increases with confining pressure.
- Ref: X. J. Tan, W. Z. Chen, H. Y. Liu, and A. H. C. Chan, "Stress-strain characteristics of foamed concrete subjected to large deformation under uniaxial and triaxial compressive loading," Journal of Materials in Civil Engineering, vol. 30, no. 6, pp. 1–10, 2018.

Tikalsky et al.... studied the freeze-thaw durability of cellular concrete and proposed an improved freeze-thaw test method. They reported that depth of absorption was considered as a critical predictor in developing freeze-thaw-resistant concrete, which will contribute to promote effectiveness in terms of using FC as insulation material for tunnels in cold regions.
- Ref: P. J. Tikalsky, J. Pospisil, and W. MacDonald, "A method for assessment of the freeze–thaw resistance of reformed foam cellular concrete," Cement and Concrete Research, vol. 34, pp. 889–893, 2004.

Sun et al... explored the influence of different foaming agents on compressive strength, drying shrinkage, and workability of FC, which will be helpful to determine specification and implementation details.
- Ref: C. Sun, Y. Zhu, J. Guo, Y. M. Zhang, and G. X. Sun, "Effects of foaming agent type on the workability, drying shrinkage, frost resistance and pore distribution of foamed concrete," Construction and Building Materials, vol. 186, pp. 833–839, 2018.

Amran et al... reviewed the composition, preparation process, and properties of FC...
- Ref: Y. H. M. Amran, N. Farzadnia, and A. A. A. Abang, "Properties and applications of foamed concrete: a review," Construction and Building Materials, vol.101, pp. 990–1005, 2015.

[T]he focus of... Ramamurthy et al... is to classify literatures on foaming materials, foaming agents, cement, fillers, mix proportion, production methods, fresh and hardened properties of FC, etc.
- Ref: K. Ramamurthy, K. K. K. Nambiar, and G. I. S. Ranjani, "A classification of studies on properties of foam concrete," Cement and Concrete Composites, vol.31, no.6, pp.388–396, 2009.

The objective of this review is to highlight engineering properties, material properties, and the practical applications in tunnel and underground engineering.

There is a confusion... between FC and similar materials in early literatures, i.e., aerated concrete and air-entrained concrete... However, one definition (i.e., FC is defined as a cementing material with the minimum of 20% foams by volume in the mixed plastic mortar) introduced by Van Dijk... clearly distinguish the FC from aerated concrete... and air-entrained concrete... The closed air-voids system in FC notably reduces its density and weight and at the same time produces efficient insulation and fire resistance capacity...
- Ref: S. Van Dijk, "Foam concrete," Concrete, vol. 25, pp. 49–54, 1991.

The first Portland cement-based FC was patented by Axel Eriksson in 1923, and then, small-scale commercial production activities were launched... Valora carried out the first comprehensive investigation in the 1950s...
- Ref: R. C. Valore, "Cellular concrete part 1 composition and methods of production," ACI Journal Proceedings, vol. 50, pp. 773–796, 1954.

Rudnai... and Short and Kinniburgh... [in 1963] systematically reported the composition, properties, and applications of the FC...
- Ref's: 1) G. Rudnai, Lightweight Concretes, Akademikiado, Budapest, Hungary, 1963. 2) A. Short and W. Kinniburgh, Lightweight Concrete, Asia Publishing House, Delhi, India, 1963.

FC was initially envisaged as a void filling, stabilization, and insulation material...
- Ref: K. Marcin and K. Marta, "Mechanical characterization of lightweight foamed concrete," Advances in Materials Science and Engineering, vol. 2018, pp. 1–8, 2018.

The booming development of this new constituent material in buildings and constructions was enhanced in the late 1970s... A government-oriented assessment on FC could be seen as a milestone event to further widening FC applications.
- Ref: M. R. Jones and A. Mccarthy, "Preliminary views on the potential of foamed concrete as a structural material," Magazine of Concrete Research, vol.57, no.1, pp.21–31, 2005.

Over the past 30 years, FC are widely used for the bulk filling... ditch repair, retaining wall...bridge abutment backfill... slab structure of concrete floor... and housing insulation... etc. ...Currently, people are increasingly interested in using it as a nonstructure or semistructure member for underground engineering, such as grouting works for tunnels, damage treatment, and liner structures.

The basic components of FC consist of (1) water, (2) binder, (3) foaming agent, (4) filler, (5) additive, and (6) fiber.

The water requirement for constituent material depends on composition, consistency and stability of the mortar body...
- Ref: K. Ramamurthy, K. K. K. Nambiar, and G. I. S. Ranjani, "A classification of studies on properties of foam concrete," Cement and Concrete Composites, vol.31, no.6, pp.388–396, 2009.

[L]ower water content leads to a hard mixture... easily resulting in bubble bursting...
- Ref: E. K. K. Nambiar and K. Ramamurthy, "Models relating mixture composition to the density and strength of foam concrete using response surface methodology," Cement and Concrete Composites, vol. 28, no. 9, pp. 752–760, 2006.

[H]igher water content causes mixture too thin to accommodate bubbles... causing bubbles separating from the mixture...
- Ref: E. K. K. Nambiar and K. Ramamurthy, "Influence of filler type on the properties of foam concrete," Cement and Concrete Composites, vol. 28, no. 5, pp. 475–480, 2006.

The American Concrete Institute (ACI) recommends that mixed water should be fresh, clean, and drinkable...

Cement is the most commonly used binder. The ordinary Portland cement, rapid hardening Portland cement, calcium sulphoaluminate cement, and high-alumina can be used in ranges between 25% and 100% of the binder content...
- Ref's: 1) M. R. Jones and A. Mccarthy, "Preliminary views on the potential of foamed concrete as a structural material," Magazine of Concrete Research, vol.57, no.1, pp.21–31,2005. 2) E. P. Kearsley and P. J. Wainwright, "The effect of high fly ash content on the compressive strength of foamed concrete," Cement and Concrete Research, vol. 31, pp. 105–112, 2001.

The foaming agent determines FC density by controlling generation rate of the bubbles in cement paste. The resin-based was one of the earliest used... [S]ynthetic, protein-based, composite and synthetic surfactants have been derived and developed... the most frequently used are synthetic and protein-based...
- Ref: S. S. Sahu, I. S. R. Gandhi, and S. Khwairakpam, "State-of-the-art review on the characteristics of surfactants and foam from foam concrete perspective," Journal of the Institution of Engineers (India): Series A, vol. 99, no. 2, pp. 391–405, 2018.

Various fillers such as silica fume, fly ash, limestone powder, granulated blast furnace slag, and fly-ash ceramicite... have been widely adopted... to enrich FC mechanical performances... Addition of these fillers is helpful to improve mix proportion design, long-term strength, and reduce costs. In addition, some fine aggregates such as fine sand... recycled glass powder... and surface modified chip... are commonly used for production of high-density FC.

Commonly used additive includes the water reducer, water-proofing additive, retarder, coagulation accelerator, etc. Plasticizers are... considered to enhance compatibility... [T]hey are defined as water reducers to improve performance of fresh concrete... and there is no notable impact on concrete segregation...
- Ref's: 1) S. K. Agarwal,I. Masood, and S. K. Malhotra, "“Compatibility of superplasticizers with different cements," Construction and Building Materials, vol. 14, pp. 253–259, 2000. 2) A. Zingg, F. Winnefeld, L. Holzer et al., "Interaction of polycarboxylate-based superplasticizers with cements containing different C3A amounts," Cement and Concrete Composites, vol. 31, no. 3, pp. 153–162, 2009.

A variety of fibers are added into FC so as to improve strength and reduce shrinkage. They are mainly polypropylene... glass and polypropylene... red ramie... palm oil, steel... coconut... waste paper cellulose... [and] carbon... which usually introduced in ranges between 0.2% and 1.5% of the mixture volume.

A Building System Based on Foam Concrete (1998)

...Cast Between Stay-in-Place Cement-Board Forms, Final Report CPAR-SL-98-4 August, 1998, by Philip G. Malone, William N. Brabston, Joe G. Tom, Roger H. Jones, Jr. Construction Productivity Advancement Research (CPAR) Program, United States Army Corps of Engineers, Waterways Experiment Station. A source.

This CPAR project was undertaken to test, demonstrate, and commercialize a new construction system... [which] employs stay-in-place forms made from fiberglass-reinforced cement boards.

Foamed concrete is also referred to as aerated or cellular concrete. Foamed concretes are lightweight concretes [typically... with densities ranging from 320 to 1,920 kg/m³ (20 to 120 lb/ft³)] that are prepared by adding air cells... typically... from 0.1 to 1 mm (0.004 to 0.04 in.) in diameter (Aldrich and Mitchell 1976).
- Ref: Aldrich, C. A., and Mitchell, B. J. (August 1976). "Strength permeabilities, and porosite of oilwell foam cement," Journal of Engineering for Industry, 1103-1106.

The foamed concrete used in this investigation was a 500- to 880-kg/m³ (31-to 55-lb/ft³) mixture that did not contain aggregate. Admixture materials, dispersing agents, chopped synthetic fiber, and pozzolans were added to the foamed concrete to improve the strength and toughness and produce a more uniform material. The particular type of foamed concrete prepared for this research program would be classed as a neat-cement cellular concrete modified with admixtures (Legatski 1994).
- Ref: Legatski, L. A. (1994). "Cellular concrete." Significance oftests and properties of concrete and concrete-making materials. 4th ed., Klierger, P., and Lamond, J. F., ed., Publication 169C, American Society for Testing and Materials, Philadelphia, PA, 533-539.

Foamed concrete is a desirable material... because of its durability, thermal-insulating, and fire-retarding properties. The low density of foamed concretes produces a substantial reduction in the dead weight of the structures in which it is used.

Foamed-concrete panels are... an economical component in construction because they are not subject to attack by insects or fungi. Foamed concrete will not degrade or depolymerize because of oxidation or photolytic reactions. In the event of fire, foamed concrete will slow the spread of the fire and will not emit smoke or toxic fumes (Short and Kinniburgh 1981, 1978).
- Ref: Short, A., and Kinniburgh, W. (1981). "The structural use of aerated concrete," The Structural Engineer 39(1), 1-16.

As the density of foamed concrete decreases, the strength properties and thermal conductivity decrease... Foamed concretes are generally used in nonstructural applications such as roof decks over metal formwork, void-filling grouts, and shock-absorbing materials for special applications.

Foamed-concrete blocks or panels are produced as cast-in-place (or cast-onsite) or precast units. Precast blocks or panels are generally manufactured by using chemical additives to generate gas bubbles in the concrete mixture. ...[C]uring is typically done under high-pressure steam.

Cast-onsite operations typically use rotating drum or paddle mixers. The cellular structure is produced by introducing a preformed, aqueous-based foam similar to a fire-fighting foam.

The new method of using cast-in-place foamed concrete with stay-in-place forms... offers several advantages. ...[It] can be adapted to a variety of requirements, and the new construction system... [a]llows hollow spaces to be blocked out in the walls for the installation of utilities or for steel-reinforced concrete pilasters that are integral with the wall.

The strength of foamed concrete made with conventional portland cement can be maximized by combining the mixture design that offers the highest paste strength with the optimum mixing techniques. Previous engineering studies (Pier and Pahl 1994) show that for a given density of foamed concrete, the strength... increases as the strength of the cured paste increases...

High-strength concretes designed with conventional materials typically improve the strength of the cured concrete by reducing the water/cement ratio (w/c) using a high-range water-reducing admixture (HRWRA) and by replacing up to 15 percent of the mass of cement with silica fume. ...The addition of silica fume... allows the calcium hydroxide formed by the hydration of the cement to react and form additional calcium silicate hydrate gel that increases the strength of the paste. The design strategy used in this study involved investigating a silica-fume replacement of up to 15 percent and the use of high-range water reducers that allowed samples with w/c's as low as 0.44 to be prepared.

Pier and Pahl (1994) also found that the strongest foamed concretes were made without using any fine aggregate. The fine-aggregate particles acted as stress concentrators, and samples made with any fine aggregate were weaker than the neat-cement formulations.
- Ref: Pier, J., and Pahl, M. H. (1994). "Aufbau und Festigkeit Zementgebundener Schaummortel." Zement-Kalk-Gips 47, 697-702.

An organic fiber (nylon) was used in the mixture in quantities that are approximately 1 percent by volume of the mixture... to increase the fracture toughness of the mixture.

The character of the foaming agent (synthetic organic or various types of hydrolyzed protein) can produce significant changes in strength (Pier and Pahl 1994). Animal protein-based foaming agents and synthetic foaming agents were both evaluated in this study.
- Ref: Pier, J., and Pahl, M. H. (1994). "Aufbau und Festigkeit Zementgebundener Schaummortel." Zement-Kalk-Gips 47, 697-702.

[I]nvestigators examined several different types of mixers and developed a technique for mixing that involved the use of a high-shear mixer to make a paste and a paddle mixer to blend foam and fiber with the paste.

Three important variables, the proportion of silica-fume replacement, the type of HRWRA, and the w/c, were evaluated... A methocellulose thickening agent (Methocel F4M, Dow Chemical Co...) was added to each batch to reduce the rate of settling of the cement particles. The mixing operation... involved dry blending the Methocel with portland cement in a 7-to-l by volume mixture prior to adding the cement to the water in the high-shear mixer. The paste was prepared by combining the water, HRWRA, dispersing agent, cement, and silica fume in a 0.36-m³ (12-ft³) capacity high-speed shear mixer. The addition of foam adds water to the mixture, and the quantity of the water depends on the density of the foam. ...[I]t was necessary to add sufficient water to the high-shear mixer to get the cement paste to mix efficiently and to flow out of the mixer.

[P]aste was removed from the high-shear mixer and placed in a Stone Model 1265PM paddle mixer... Litecrete R11937 foaming agent... was used... diluted 39 to 1 by volume, and the diluted solution was foamed using a Cellufoam Systems Model 620 Foam Generator... Foam was added to adjust the density to the target level, and fiber was added to the foamed concrete. The foamed concrete was then removed from the paddle mixer and placed in the form...

Silica-fume replacement above 20 percent presents problems with regard to water demand even when HRWRA is used. ...In two of the three attempts to place foamed concrete with a 20-percent silica-fume replacement, the foamed concrete collapsed.

The most successful placements and highest strengths were obtained with 10-percent silica-fume replacement. The best flow characteristics and best strengths were obtained with a mixture that contained 10-percent silica-fume replacement and at w/c = 0.62.

The HRWRA ingredient that performed best was Sikament S-10 ESL (Sika Corp...) ...a synthetic HRWRA formulated around a vinyl co-polymer. The manufacturer recommends this HRWRA for use in concretes containing silica fume or other micro-silica products. The manufacturer's recommended addition rate is 390 to 1,300 ml/100 kg of cement. Additions of... 1,200 ml/100 kg of combined cement and silica fume were used...

Typically, the samples from the lowest part of the column were 16 to 32 kg/m³ (1 to 2 lb/ft³) denser than the samples from the top of the column. In extreme cases, variations as high as 320 kg/m³ (20 lb/ft³) were noted. Denser samples are stronger. In these low-density concretes, a 16- to 32-kg/m³ (1- to 2-lb/ft³) density difference can increase the unconfined compressive strength by 100 kPa (14.5 psi) or more.

The target densities for the panels were set at 480 to 560 kg/m³ (30 to 35 lb/ft³) with target unconfined compressive strengths (28 days) of over 895 kPa (130 psi).

A high temperature can cause the foam to collapse because it expands the gas bubbles in the concrete and lowers the surface tension in the foam. Based on the results of the temperature measurements, a synthetic foaming agent that was considered to have better tolerance at high temperatures was substituted for the animal protein-based foam that had been used... where the foamed concrete had collapsed.

The goal was to produce materials that had an air-dried density under 640 kg/m3 (40 lb/ft3) and an unconfined compressive strength of over 690 kPa (100 psi) after curing for 28 days...

The composition used in the optimum mixture proportion is presented in Table 6.

Table 6 Optimum Concrete Mixture
Material	Mass/Volume
Portland cement, Type I	78.2 kg (472 lb)
Silica Fume, 10% of Cement	7.82 kg (47.2 lb)
Water	95 kg (209 lb)
Actual Water/Cement Ratio	0.50
HRWRA	2.4 L
Stabilizer	113g
Nylon Fiber	453.6 g
Preformed Foam	0.57 m3 (20.11 cf)

The peak interior temperatures in the panels reached approximately 30°C above ambient... The temperature changes did not produce any thermal or shrinkage cracking. The foam collapse observed stopped when the synthetic foaming agent was used. No problems with regard to flash setting or loss of workability were noted in the temperature ranges observed... [N]o special procedures (such as cooling the ingredients) or the use of low-heat cements are needed in foamed-cement panel production for the panel sizes used in this investigation when ambient temperatures are on the order of 20 to 25 °C.

Concrete Technology (1982)

: Theory and Practice by M.S. Shetty, A.K. Jain

Basically there is only one method for making concrete light i.e., by the inclusion of air in concrete. This is achieved in actual practice by three different ways.
(a) By replacing the usual mineral aggregate by cellular porous or light-weight aggregate.
(b) By introducing gas or air bubbles in mortar. This is known as aerated concrete.
(c) By omitting sand fraction from the aggregate. This is called 'no-fines' concrete.

[S]tructural light-weight concrete is... strong enough to be used for structural purposes. Light-weight concrete can... be classified on the purpose for which it is used, such as structural light weight concrete, non-load bearing concrete and insulating concrete. The aerated concrete which was mainly used for insulating purposes is now being used for structural purposes sometimes in conjunction with steel reinforcement. The aerated concrete is more widely manufactured and used in the Scandinavian countries; whereas in U.K., France, Germany and U.S.A. owing to the production of large scale artificial industrial light-weight aggregate, light-weight aggregates concrete is widely used.

There are several ways in which aerated concrete can be manufactured.
(a) By the formation of gas by chemical reaction within the mass during liquid or plastic state.
(b) By mixing preformed stable foam with the slurry.
(c) By using finely powdered metal (usually aluminium powder) with the slurry and made to react with the calcium hydroxide liberated during the hydration process, to give out large quantity of hydrogen gas. This hydrogen gas when contained in the slurry mix, gives the cellular structure.
Powdered zinc may also be added in place of aluminum powder. Hydrogen peroxide and bleaching powder have also been used instead of metal powder. But this practice is not widely followed at present.

Gasification method is of the most widely adopted methods using aluminium powder or such other similar material. This method is adopted in the large scale manufacture of aerated concrete in the factory wherein the whole process is mechanised and the product is subjected to high pressure steam curing i.e... the products are autoclaved. Such products will suffer neither retrogression of strength nor dimensional instability.

The practice of using preformed foam with slurry is limited to small scale production and in situ work where small change in the dimensional stability can be tolerated. But... any density desired... can be made in this method.

"Properties of air-entrained concrete at early ages" (1960)

Ugur Ozoguz, Thesis T 1243 - Open Access, Missouri School of Mines and Metallurgy. Masters Theses. 2679.

[T]he addition of a moderate amount of air to any concrete mix will bring a marked increase in resistance to the disintegrating effects of freezing and thawing.

The application of air-entrainment to the concrete mix, for the improvement of its durability, workability and uniformity, is one of the most important developments in concrete technology.

The improvement in durability with the use of proper amounts of entrained air in concrete is so great that variations in the water-cement ratio, within the usual working range, do not have the same significance as formerly.

The deliberate addition of air to concrete seemed, from a superficial examination, to be contradictory to the principle that high density is a pre-requisite of high quality. But the concept of density of concrete actually means: freedom from honeycombing and large voids resulting from inadequate consolidation or from segregation. Air entrainment, by enabling some reduction in water-cement ratio, tends to improve the quality of the concrete paste, and by improving workability tends to reduce segregation and improves consolidation of the concrete.

First experiments proved that, to obtain desirable properties of air-entrained concretes, entrained air must be approximately three percent above that which is normally present in the concrete, this brings the total amount of air to between four and five percent...
- Ref: "Ready Mix Men Discuss Air-Entrainment" Concrete (March 1945) Vol. 53, No. 3, Page 10.

There are various air entraining admixtures for concrete that can be either interground with the cement during the manufacturing process or added separately at the mixer. Many of them are essentially saponifying agents, they react with the alkaline constituents of the cement to form soap and from the soap, form minute air bubbles.

[A]ir-entrainment adds to the fluidity or slump of concrete and it is possible to restore the initial degree of stiffness by adding solids or subtracting water. Air cannot be added to a mixture without introducing unbalances in consistency and yield of the plastic concrete. ...[T]he strength of the hardened concrete depends on the consistency of the plastic concrete. Experiments have shown that for the same workability, less water is required than for ordinary concrete.

Concrete Technologies (1958)

Vol. 1 Properties of Materials by D. F. Orchard, entries are from Ch. 4 Lightweight Concretes, 1973 3rd edition, unless otherwise indicated.

The chief ways of producing aerated or gas concrete are by mixing air entraining agents with cement or cement and sand in special high speed or whisking mixers, by adding a given quantity of pre-formed foam to a cement or a cement sand mortar in an ordinary mixer and by adding aluminum or zinc powder to a cement mortar.

Aerated concrete has a very high drying shrinkage but this can be reduced by high pressure steam curing in which case fly ash or natural pozzolana can with advantage be introduced to the mix.

Owing to its high drying shrinkage... [lightweight concretes] use for cast in situ should be restricted to cases where shrinkage cracks are not of much importance.

Lightweight concrete is normally accepted as that having a density range between 25 and 110 lb per cu ft, but even lower densities can be used when it is required solely for insulating purposes.

Lightweight concrete can be produced in three ways:
1. By omitting the fine aggregate. This is called a 'no-fines' concrete.
2. By using lightweight aggragate.
3. By using lightweight aggregate and producing what is generall known variously as 'aerated concrete', 'cellular concrete', 'gas concrete', 'porous concrete', and 'foamed concrete'. This should not be confused with air entrained concrete which has a weight nearly equal to that of ordinary concrete and in which the proportion of air is limited to about 9 per cent.

Aerated, cellular or gas concrete can be made in weights ranging from about 25 lb per cu ft or even less, to 110 lb per cu ft. Its most useful range is perhaps between 40 and 60 lb per cu ft.
It can produced in the following ways:
1. By mixing air entraining agents with cement or cement and sand in special high speed or whisking mixers. If an ordinary mixer is used it is doubtful if sufficient air would be entrained to obtain a density as low as 90 lb per cu ft. The Cheecol process belongs to this class. 2. By making foam and and adding a given quantity of this to a cement or cement and sand mortar in the mixer. An ordinary mixer is suitable for this method. The Pyrene process belongs to this class. 3. By adding hydrogen peroxide (H₂O₂) to the concrete. 4. By the use of calcium carbide (Ca₂C₂). 5. By adding aluminum powder or zinc powder to a cement mortar.

Very careful mixing of the mortar with the air entraining or other agent is essential in all cases if a uniform result is to be obtained.

If the lightest concretes (25 lb per cu ft and under) are required a neat cement mortar is used, but for heavier weights (40 lb per cu ft and above) sand, preferably very fine, may be added up to a cement/sand ratio... of 1 to 4. A higher strength/weight ratio can be obtained if cement only is used, but the addition of sand cheapens the product.

The Use of Air Entraining Agents... The normal density produced from this system ranges from 60 to 100 lb per cu ft and the proportion of air entraining agent may be about 0.25 per cent of the mix. The quantity of air entraining agent, the cement/sand ratio, the speed of the mixer and the time of mixing are the chief factors...

The Use of Preformed Foam... [A]lmost any desired density of concrete can be produced... dependent almost entirely on the amount of foam added. About two per cent by volume of a foaming agent is added to the water and mixed with compressed air in a mixing tube. ...The foam is delivered ... direct into the mixer in which the cement or cement sand mortar has previously been prepared. The product can be cast in situ or used for making precast blocks.

Laboratory Studies of Concrete Containing Air Entraining Admixtures (February 1946)

Charles E. Wuerpel, Journal of the American Concrete Institute, Vol. 17, No. 4, Page 385.

The effects of the incorporation of each of nine different air-entraining admixtures in concrete were investigated by the making of a large number of batches of concrete under carefully controlled laboratory conditions. The results of tests on the plastic and hardened concrete specimens from batches made in parallel with and without each admixture are presented and discussed.

Different air entraining agents produce different amounts of air entrainment, depending upon the elasticity of the film of the bubble produced, and the extent to which the surface tension is reduced. Similarly, different quantities of air entraining agents will result in different amounts of air entrainment.

Water/cement ratio is one of the important factors affecting the quantity of air. At very low water/cement ratio, water films on the cement will be insufficient to produce adequate foaming action. At intermediate water/cement ratio (viz. 0.4 to 0.6) abundant air bubbles will be produced. But at a higher water/cement ratio although to start with, a large amount of air entrainment is produced, a large proportion of the bubbles will be lost progressively with time.

The grading of aggregate has shown good influence on the quantity of air entrainment. It was established that the quantity of air increased from the lowest fineness modulus of sand to a peak at about F.M. of 2.5, and, thereafter, decreased sharply. The sand fraction of 300 and 150 microns showed a significant effect on the quantity of air entrainment. The higher quantity of these fractions resulted in more air entrainment.

The amount of air entrainment is found to increase with the mixing time up to a certain time and thereafter with prolonged mixing the air entrainment gets reduced.

The temperature of concrete at the time of mixing was found to have a significant effect on the amount of air entrainment. The amount of air entrainment decreases as the temperature of concrete increases.

The constituents of the cement especially the alkali content plays an important part in the entrainment of air in concrete. Similarly, the fineness of cement is also a factor.

Air content is... reduced by the process of compaction, on account of the movement of air bubbles to the surface... [A]s much as 50 per cent of the entrained air may be lost after vibration for 2 1/2 minutes and as much as 80 per cent may be lost by vibration for 9 minutes.

[A]dmixtures used in conjunction with air entraining agents will... significantly affect the amount of air entrained. The use of fly ash in concrete will reduce the amount of air entrained. Similarly, the use of calcium chloride also has the tendency to reduce and limit air entrainment.

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