LIGHT WEIGHT CONCRETE

A Technical Seminar  On By: Hemanth K.R

Under the Guidelines: Prof & Head Dept of Civil Engg.

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CONCRETE IS NOTHING BUT MIXTURE OF AGGREGATES AND BINDER, WHICH IS USED BY MAN FROM THOUSANDS OF YEARS.

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THE PEOPLE STARTED THINKING ABOUT MAKING STRUCTURE LIGHT.

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Let's TAKE A LOOK ON RESULT OF THEIR THINKINGS………..

HISTORY •

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Romans appeared to have used Light weight Concrete in 2nd century, in the construction of  44m dia dome of Pantheon 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. The first commercial scale production of light weight aggregate manufactured in Kanas city, in 1917, named as “HAYDITE”.

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Other expanded clay aggregates such as “GRUELITE” “TERLITE” “ROCKLITE” were marketed by various American firms In 1930, hollow globular burnt clay particles known as globulite developed in Germany. Industrial waste „cinder‟ is converted into light weight aggregate by secondary burning and marketed in the name  – “AGLOPYRITE”. 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? •

“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 !!!. •

“The LWC is a concrete capable 0f hardening, to a mass having oven dry density not more than 1800 Kg/m3 ”. •

“Concretes having 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      

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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 porous ness). 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 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 ?? •

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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   Artificially( 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  Light Weight Concrete

Classification based on RILEM 

Fully compacted concrete

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Partially compacted concrete

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 No finer concrete Aerated concrete produced by chemical  process (gas concrete) Aerated concrete produced by physical process (foam concrete)

Classification based on density and strength 

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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 of Production

There are three methods to produce L.W.C. They are, 

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Omitting fine sized aggregates while grading i.e. No Fines Concrete. Using cellular porous aggregates i.e. Light  Weight Aggregate Concrete. Introducing air or gas in to concrete i.e. Aerated Aerated Concrete.

 No Fines Concrete Concrete  

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fine aggregate fraction is omitted Only cement and coarse aggregates are used (19mm  –  9mm). It contains many uniformly distributed voids. Density varies from 2/3rd to3/4th of conventional concrete 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.

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In case of No fines concrete, W/C ratio must  be selected very carefully The density of No fines concrete varies from 1600-1900 kg/m3. It can be reduced up to 360 kg/m3 by using LWA

Disadvantages 

Possesses poor workability

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Low compressive strength

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Low flexural strength

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High permeability

Light weight Aggregate concrete One of the oldest and common method of  producing L.W.C  Light weight aggregates, either Natural or  Artificial,are used in concrete. 

Light Weight Aggregates These are naturally available aggregates, like Pumice  Dolomite  Scoria   Volcanic cinders  Saw dust  Rice dust 

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Expanded clay and shales- Produced by heating of  clay and shale heating up to point of incipient fusion Expanded slate- Produced by heating rapidly to higher temperature so as not allow gases to escape 

Foamed blast furnace slag

Cooling slag with controlled amount of water, the steam is tapped inside the mass, results in L.W.A. known as foamed slag or expanded slag.

Pulverized fuel ash

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fly ash is mixed with limited amount of water and made into pellets and then introduced to a temperature of 1000-1200 degree c, from which it is converted into aggregate. Most commonly used aggregate because of  it’s high strength/ density ratio and less shrinkage value.  – 

Aerated concrete or Cellular concrete General composition is mortar, suitably aerated Called as foam concrete, cellular concrete, gas cone etc.  In India, the factories manufacturing aerated concrete are Siporex, vayuthan, celcrete . 

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Methods of aeration:

By the formation of gas by chemical reaction within the mass during liquid or plastic stateFinely powdered Al or Zn is added to the slurry which in turn reacts with ca(OH)2 generated during hydration of cement. H2 gas liberated by such reaction will lead to cellular concrete. It is used normally in precast concrete factories

By mixing preformed stable foam with slurryStable foam is mixed with slurry thus causing cellular structure when the slurry sets and hardened. It is suitable for small scale productions and in situ works.

Classification of Aerated concrete : 

As per IS 6072 – 1971 and IS 6073 – 1971, the aerated concretes are classified into five groups based on their density, as follows GROUP

DRY DENSITY Kg / m3

Min. Compressive Strength ( Kg / cm2)

Class A

851 to 1000

70

Class B

751 to 850

60

Class C

651 to750

50

Class D

551 to 650

35

Class E

451 to 550

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Implementation Implementatio n of L.W.C •

Since the strength of L.W.C. is low, it is used in the construction of roof slabs, small houses with load bearing walls etc.

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It is also used in the construction of stairs, windows, garden walls, etc.

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In large buildings also, this is used in the construction of partition walls.

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These are moulded in the form of slabs and used as thermal insulators inside the building.

al i s e t h e l o w c o s t   “T o r e al co nstruction, w e have  t o i m p l em e m e n t L i g h t w e ig ig h t   Concrete first”.

Conclusion : •

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Since, the Light weight concrete is of low compressive strength; this can not be used for  the construction of structural members such as beams, columns, etc. But this can be effectively used in the construction of partition walls, windows, floor slabs, etc. The implementation of  light weight concrete more in the structure leads to more economy. Therefore we can conclude that, “To achieve the low cost construction, first we have to implement Light weight Concrete” .

1.Light 1. Light Weight Concretes by Mr. M.G. Srinivasan 2.Concrete 2. Concrete Technology by A.M. Neville & J.J. Brooks 3.Excerpts from Internet Downloading