Engineering

"[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"

"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."

"[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..."

"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."

"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 (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..."

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

"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..."

"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..."

"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."

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

"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."

"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."

"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..."

"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."

"[A]dmixtures used in conjunction with air entraining agents will... significantly affect the amount of air entrained. The use of 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."

"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."

"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 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 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."

"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 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."

"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."

"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."

"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]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."

"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."

"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."

"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."

"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."

"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..."

"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."

"[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."

"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."

"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."

"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."

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

"[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."

"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)."