seminar on light weight concrete

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Brief History:

Romans appeared to have used Light weight Concrete in 2nd century, in the

construction of 44m dia dome of Pantheon. But due to rarity and non-availability

of porous light weight aggregates, the search for artificial aggregates began in

the beginning of 20th century. In 1907, Ottoman [Hungarian] developed a method

of converting Blast furnace slag in to foamed structure, which is the first

milestone of Light Weight Concrete.

But, the first commercial scale production of light weight aggregate manufactured

in Kanas city, in 1917, named as “HAYDITE”.

Subsequently, other expanded clay aggregates such as “GRUELITE” “TERLITE”

“ROCKLITE” were marketed by various American firms. In 1930, Germany

developed hollow globular burnt clay particles known as globulite.

Industrial waste ‘cinder’ is converted into light weight aggregate by secondary

burning and marketed in the name – “AGLOPYRITE”.

The mail historical point is during 2nd world war, 105 light weight ships were built

using Light weight concrete.

In India, Pune based company, B.G.Shirke Construction Company Ltd is

manufacturing steam cured, light weight, autoclaved and strong floor slabs, roof

slabs, panels, lintels etc. with the brand name “SIPOREX”.


What is Light Weight Concrete?

        Light weight concrete can be simply defined as follows,

“These are the concretes which are much lighter than the conventional concrete,

due to different constituents and methods used in manufacturing process”.

Density of conventional concrete varies from 2400-2500 Kg/m3.But the density of

light weight concrete is in between 300-1900 Kg/m3. How great difference !!!.

As per RILEM, the light weight concrete committee “The LWC is a concrete

capable 0f hardening, to a mass having oven dry density not more than 1800

Kg/m3 ”.

As per ACI,

“Concretes have a 28 days compressive strength in excess of 175 Kg/m3 and 28

day air dried unit weight not exceeding 1850 Kg/m3”.      

Advantages over Conventional concrete :

 Reduction of Dead load due to less density.                                                                                                  

 Increases progress of work due to less weight.

 Lowers Haulage and Handling charges.

 In extreme climatic conditions, use of LWC is advisable because of high

thermal insulation (due to porousness).

 More sound and heat insulation.

 Its volume per unit weight is more than that of conventional concrete,

because of low density, results in economical construction.

 Due to low density, it reduces the size and the cost of structural members

such as beams, columns, foundations etc.

 This is advantageous in the case of tall structures which are to be

constructed on soils of low bearing capacity.

 It is eco-friendly because it gives an outlet for industrial waste such as

clinker, fly ash, slag etc. which otherwise create pollution.

How to make concrete LIGHT ??

Weight of concrete Wc is a function of weights of aggregates, binder and

volume of voids.

Wc = f [ Wca, Wfa, Wb, Wv ]

Therefore, we can reduce the weight Wc by  

 Reducing the weight of coarse and fine aggregates, i.e. use of light

weight aggregates which are occurred either Naturally (Pumice) or


( Globulite, Terlite).

 Increasing the volume of voids by one or both of following,

 Introducing air or gas into the concrete

 Remove certain fractions of fine aggregate in the concrete

so that volume of void can be increased.

Classification of L.W.C. :

 Classification based on RILEM

 Fully compacted concrete

 Partially compacted concrete

 No finer concrete

 Aerated concrete produced by chemical process (gas


 Aerated concrete produced by physical process (foam


 Classification based on density and strength

 L.W.C of Low strength and good thermal insulation having

density ranges from 250- 800 Kg/m3.

 L.W.C. of medium strength and adequate thermal insulation

having density ranges from 800 – 1400 Kg/m3.

 L.W.C. of structural strength and limited thermal insulation

having density ranges from 1400 – 2100 Kg/m3.

Methods :

To realize Light Weight Concrete, increase the pore volume of the concrete by,

 Omitting fine sized aggregates while grading  i.e. No Fines


 Using cellular porous aggregates  i.e. Light Weight Aggregate


 Introducing air or gas in to concrete  i.e. Aerated Concrete.

No Fines Concrete :

many uniformly distributed voids. Its density varies from 2/3rd to3/4th of

conventional concrete. It’s strength mainly depends on W/C ratio and A/C ratio.

W/C ratio must be in between  0.38 to 0.52  and

A/C ratio must be in between 6:1 to 10:1.

In case of No fines concrete, W/C ratio must be selected very carefully. Because,

 If W/C ratio selected is too low, then the paste will be very dry and

aggregates do not get bonded. This results in insufficient adhesion

between particles, hence reduction in strength.

 If W/C ratio is too high, then the cement paste flows to bottom. Hence,

segregation and bleeding takes place particularly when vibrated. This also

leads to reduction in strength.

The density of No fines concrete varies from 1600-1900 kg/m3. but it can be

reduced up to 360 kg/m3 by using LWA. And it’s compressive strength varies

from 14 – 140 kg/cm2

But it has some disadvantages,

 possesses poor workability

 low compressive strength

 low flexural strength

 high permeability

therefore nowadays it is not widely used as L.W.C.

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