No_4_1956 — Page 73

AERATED CEMENT AND CONCRETE

by K.A. Luna

Dyestuff Division, Imperial Chemical Industries Ltd.. Manchester, England)

An increasing appreciation, on the part by mechanical agitation. At the recom- FC solution by а standardized foarn of architects and building contractors, of mended dosages Aphrosol FC has no harm equipment, either by mechanical high- the merits of foamed cement and concrete ful effect on the strength or durability of for heat insulation in modern building the final aerated cement or concrete. construction, has given rise to a growing

accurate as

speed stirring in a container of restricted volume or by air foaming through a baffle tube.

the

interest in the technique of producing such The Entraining Method materials. Although there is no mysterious

The ideal device is a continuous foam- This is the simpler of the two methods ''know-how** about the production of mentioned above for making aerated producing unit operating by compressed aerated cement or concrete, it is necessary cement ог concrete and it requires no air which delivers, from a foam gun, to establish a sound working routine and special foam apparatus. Mixing is carried required texture foam at the 40-50 times adhere to it reasonably carefully to ensure out in conventional type mixers, prefer- expansion, with a known delivery rate. satisfactory and reproducible results.

ably of the non-tilting type. Control of The appropriate volume of foam (aera- The essential part of the routine is, of the density of the mix is not quite as tion) to be added can then be translated

the incorporation of a fairly large

in the prefoaming method into time of delivery of foam, depending course, volume of air

(described later) but the method has the on batch size and aeration required. in the form of innumer- able small bubbles into mixes consist-

merit of simplicity and has much to com-

This method is more positive than the ing of cement and water, with or without mend it in cases where the provision of the addition of sand. The necessary air special equipment would be unwarranted. entraining method and is not dependent on mechanical agitation to induce aera- is incorporated in one of two ways: either Usually the best procedure is to charge tion; hence mixing can be carried out in by agitating the mix in such a way as half the sand, followed by the water and any type of mixer capable of folding the to produce aeration, or by adding the air Aphrosol FC, mixing these well before foam into the aqueous slurry.

It is gen- to the mix in the form of a highly ex- adding the cement and the rest of the sand erally best to add the desired amount of panded foam prepared separately.

together. The order of mixing is not foam gradually (at first, at any rate) to critical, however. The amount of water ensure even incorporation throughout the should be sufficient to allow the mix to mass of the slurry. Generally, two but not excessive since the fluidity will foam addition be thrown about vigorously in the mixer, minutes mixing after completion of the is sufficient before dis- in any case tend to increase as

aeration charging. proceeds, and a high free water content in the mix may result in subsequent Lightweight aerated cements with den- shrinkage of the aerated concrete in sities, as

used for insulation purposes, moulds before the set.

may be prepared satisfactorily by the pre- foaming technique. The excellent proper- ties of Aphrosol FC are an important factor in the achievement of uniformly satisfactory results.

re-

In either case a foaming agent is quired, to encourage air entrainment (and also to prevent loss of the air entrained) in the first method, and to act as a tem-

and measurable

porary

for the air in the second case,

Aphrosol FC

"container"

been The Pre-foaming Method

One foaming agent of outstanding ef-

Progress of aeration is easily followed ficiency is Aphrosol FC, specially develop- ed for use

in the production of foamed by weighing a known volume of the mix cement and concrete

intervals, in a container of suitable by the Dyestuffs at Division of Imperial Chemical Industries dimensions. Limited. Not only has Aphrosol FC, exhaustively tested in the concrete nology laboratory of I. C. I. Dyestuffs Division in Manchester, but it has been successfully used on an industrial scale in house construction and other building work over the past few years.

an

tech-

Successful Large-scale Applications

It was

soon after the war ended that

Much more economical use of foaming Aphrosol FC had its first important large-

in the agent is achieved

pre-foaming scale application, when it was selected as method. In addition, ultra-lightweight the foaming agent for use in the manu- aerated cement, which cannot be prepar- facture of wall sections of metal-encased ed in conventional types of mixers using foamed cement for prefabricated houses, the entraining method, are easily produc- many thousands of which were erected in Aphrosol FC is a blended mixture of ed by the preformed foam teachnique.

Great Britain in the years immediately aromatic sulphonate (one of the so-

following the war. called modern "surface-active agents'') Briefly, the aqueous slurry of sand and/-

Later applications have been in the that has powerful wetting and foaming or cement is acrated by the addition of

in situ, of floor and roof properties, and other ingredients which a foam of fine bubble texture, prepared fabrication,

for heat improve the stability of the foam pro- by the expansion of an aqueous 4% solu- screeds in industrial buildings duced. Owing to this balanced combina- tion of Aphrosol FC to 40-50 times the insulation purposes, in party-walls of flats tion of properties it is possible to expand liquid

The success of this and

airborne office buildings to give a very dilute solution of Aphrosol FC to method depends on the foam texture and sound insulation, and generally to reduce many times its volume of foam simply controlled expansion of the 4% Aphrosol dead weight on foundations.

volume.

GYSLING OZONE PRODUCER

Ozone, also know as "active oxygen", It is claimed that it is now being produced The manufacturers claim that it not is an extremely pure gas contained in the more efficiently by electric discharges in only regenerates the air, but purifies, dis- air mostly at high altitudes. The dic the air by means of an apparatus now infects and de-odorises it as well. Ac- tionary states that it is "a condensed form being marketed under the trade name of cording to them, it requires no lubrica. of oxygen with three atoms to a molecule, "GYSLING”.

tion, no servicing, no attention; it is in- having a pungent refreshing odour". It

to of expensive operate, trouble-free and To people living under conditions is extremely active and is undoubtedly one of the causes of the feeling of exhilara- modern civilization in closed premises of completely silent. tion that possesses one at high elevations, homes, offices, workshops, etc., the ab-

of Ozone produces that sence

familiar

Ozone has been produced in the labora- feeling of stuffiness, and the Gysling ap. tory by the electrolysis of water and by paratus is designed to rectify this condi- the action of ultra-violet rays on oxygen. tion.

The local Sole Agents, Messrs. K. Caudron & Co., are willing to give free demonstrations and to supply full par- ticulars on request.

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