Foam concrete

"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)."

"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..."

"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."

"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."

"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."

"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."

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

"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."

"If [used,] ... dosage should not be more than 0.2[% by weight of cement] bwc."

"To minimize shrinkage... [water] ratio[s] should be kept as low as possible."

"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."

"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 . ...The addition of silica fume... allows the 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."

"[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."

"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."

"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."

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

"The 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 s have been derived and developed... the most frequently used are synthetic and protein-based..."

"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."

"[D]ry ingredients like cement, sand, sand + fly ash or fly ash alone shall be... thoroughly mixed to ensure even distribution... [B]locks may be de-moulded after 24 hours"

"Sample [first trial] mix proportions [by weight of water (W), ordinary Portland cement grade 53 (OPC 53 grade or (C) in Note below), fly ash (FA), and fine sand (FS) passing 4 mm IS sieve] ... are given in table- 1, 2 & 3. However, conclusive... proportions by actual trials may be worked out... for required workability, plastic density and compressive strength."

"Usually... cement content lie[s] between 300 to 500 kg/m3. ...[G]ain in strength is small above... 500 kg/m3."

"[T]rial mixes should be done... to determine workability... plastic density... [and compressive strength.] Specimens shall be cast and tested for... compliance of required specifications."

"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)."

"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."

"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..."

"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."

"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..."

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

"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."

"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..."

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

"Cement is the most commonly used binder. The ordinary , rapid hardening Portland cement, calcium sulphoaluminate cement, and high-alumina can be used in ranges between 25% and 100% of the binder content..."

"Various fillers such as , , powder, granulated blast furnace , 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. s 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..."

"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."

"Fire rating of foamed concrete is far superior to... brick work or dense concrete."

"[F]oam... shall be added in measured amount to the slurry of cement, sand, fly ash and water in the batch mixer... mixing to get uniform consistency... of desired wet unit weight..."

"After curing [per IS: 456-2000], the blocks shall be allowed to dry under shade for a period 2 to 3 weeks... to complete their initial shrinkage..."

"Ignore the amount of water... in the foam in the mix design calculation."

"Determine the amount of air (kg/m3) in the mix from... the target density of the foam."

"Fly ash is added... up to 100% of the [ordinary Portland cement] OPC content, to enhance workability and increase long-term strength... Because of greater surface area... [these] mixes have a greater water demand... [F]ly ash... leads to a more uniform bubble structure... which... improve[s] some... engineering properties..."

"Fly ash can be used as a total replacement for sand to produce... a dry density of up to 1400 kg/m3."

"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 s 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)."

"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."

"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."

"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."