Engineering

"[L]ower water content leads to a hard mixture... easily resulting in bubble bursting..."

"[H]igher water content causes mixture too thin to accommodate bubbles... causing bubbles separating from the mixture..."

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

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

"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."

"Over the past 30 years, FC are widely used for the bulk filling... ditch repair, retaining wall...bridge 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."

"FC was initially envisaged as a void filling, stabilization, and insulation material..."

"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..."

"Foamed concrete differentiates from (a) gas or aerated concrete, where the bubbles are chemically formed through the reaction of powder with calcium hydro oxide and other alkalies released by cement hydration and (b) air entrained concrete, which has a much lower volume of entrained air... for durability."

"28 days strength and dry ... vary according to its composition, largely its air voids content, but usually... range... 1.0 to 25.00 N/mm2 and 400 to 1800 kg/m3. The plastic density... is about 150 to 200 kg/m3 higher than... dry density."

"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 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."

"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."

"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 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."

"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 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."

"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 powder to a cement mortar."

"Foamed light weight concrete... bricks, blocks or poured in-situ is used for over flat roofs... cold storage walls or... s for low-rise buildings."

"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 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."

"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 , hydrazocarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylene tetramine, toluenesulfonyl hydrazide, benzene sulfonyl , and barium azodicarboxylate. While inorganic agents are NaHCO3, NH4HCO3, (NH4)2CO3, and Ca(N3)2... foams are used as insulation spray for air-sealing buildings. stabilizer is added to enhance its slurry viscosity which consists of 20% of 40% of and 40% of hydroxypropyl methyl cellulose... [T]he various foam agents are available in E-markets worldwide."

"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."

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

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

"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 -based FC technology in the year 1923... The characteristics, behaviour and structural applications of FC have been widely investigated..."

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

"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."

"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..."

"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."

"Considering that fibreglass also increases mechanical strength, this is an important factor in FC’s stability... High-strength foamed concrete is obtained by introducing (PP) fibre into the raw mix... Many of the currently used fibres have been investigated, including PP... blend of polypropylene with glass... ... ... 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)..."

"[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."

"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..."

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

"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."

"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..."

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

"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."

"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..."

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

"[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."