Architecture

"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."

"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."

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

"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."

"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."

"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."

"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."

"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."

"[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..."

"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."

"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."

"[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."

"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 powder to a cement mortar."

"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..."

"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..."

"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."

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

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

"The improvement in durability with the use of proper amounts of entrained air in concrete is so great that variations in the , 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."

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

"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."

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

"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."

"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..."

"The water requirement for constituent material depends on composition, consistency and stability of the mortar body..."

"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."

"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."

"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 powder) with the slurry and made to react with the liberated during the hydration process, to give out large quantity of gas. This hydrogen gas when contained in the slurry mix, gives the cellular structure. Powdered may also be added in place of aluminum powder. and bleaching powder have also been used instead of metal powder. But this practice is not widely followed at present."

"[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."

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

"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..."

"[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."

"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."

"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."

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

"[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."

"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."

"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."

"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 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..."

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

"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..."

"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."

"[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."