What is Light Weight Concrete? And Why Should You Care?

What is Light Weight Concrete

Generally, The Density of Conventional Concrete varies from 2200 to 2600 kg/m3. This high self-weight of concrete will make concrete uneconomical structural material so as an engineer it’s your responsibility to make economical structural buildings with your engineering skill.

The deadweight or self-weight of the concrete structure is higher compared to the imposed load which the structure has to transfer successfully to the foundation soil.

You can save great money and manpower in a multi-storey building by a slight reduction in deadweight for any structural members such as columns, beams, and slabs.

Attempts have been made during the construction process to decrease the self-weight of final concrete to boost the efficiency of cement concrete as a structural member material.

The lightweight concrete whose density varies in the range of 300 Kg/m3 to 1900 Kg/m3 has been successfully developed.

Light Weight Concrete: A Simple (But Complete) Guide you will get here.

Advantages of Lightweight Concrete

• Great reduction of dead load.
• It offers greater fire resistance.
• Structural members with smaller sections can be adopted.
• Easy in the transportation of concrete and handling cost.
• Increased in process of work due to lightweight.
• Especially taken into work where foundation soil has a low bearing capacity.
• Foundation cost reduction, particularly in the case where weak soil and tall structural.
• The thermal conductivity of lightweight concrete is low. In the case of building structure where air-conditioning is to be installed because the use of lightweight concrete gives better results in better thermal comfort so alternative power consumption is also decrease.
• Eco-Friendly: The use of lightweight concrete provides an outlet for industrial wastes such as fly ash, clinker, slag, plastic, glass powder, etc. which would otherwise pose a major problem for disposal so alternatively it also converts to environment-friendly concrete.
• Lightweight concrete gives the overall economy.
• Lower modulus of elasticity and sufficient flexibility of lightweight concrete can be beneficial in the seismic design of the structure.

How to Where To Get

The lightweight concrete is obtained in three different ways.

1. By omitting sand fraction from the aggregate. This is known as “no-fines concrete”.
2. By replacing the normal mineral aggregate, with cellular porous or lightweight aggregate. This is known as “lightweight aggregate concrete”.
3. By introducing air bubbles in mortar. This is known as “aerated concrete”.

Also Read: Concrete Mix Design as per IS CODE excel sheet

Type and use of Light Weight Aggregate Concrete

Use Of Light Weight Concrete: 2 Categories to Classification Of Light Weight Concrete.

The lightweight aggregate used in the production of lightweight concrete is classified into two categories.

a. Natural lightweight aggregate

e.g

• Pumice
• Scoria
• Rise husk
• Sawdust
• Diatomite
• Volcanic tuff
• Foamed lava

Natural lightweight aggressive

Pumice

• Pumices are rocks of volcanic origin.
• They are light-colored or nearly white and has a fairly even texture of interconnected.
• Its bulk density is 500-800 Kg/m³.
• It has been used in Roman structures.

Scoria

• Scoria is also a lightweight aggregate of volcanic origin. There is mainly availability in dark color. It is slightly weaker than pumice.

Sawdust

• Saw dusk is used as lightweight concrete in the flooring and in the manufacture of precast elements. But the availability of tannins and soluble carbohydrates.

Rice husk

• The use of rice husk or groundnut husk has been reported as a lightweight aggregate

Diatomite

• Diatomite is derived from the remains of microscopic aquatic plants called diatoms. It is also known as kieselguhr. The deposits of aquatic plants are formed beneath the deep ocean bed. The bulk density of diatomite is about 450 Kg/m³. It is also used as a pozzolanic material.

b. Artificial high-weight aggregate

e.g.

• Sintered fly ash
• Foamed slag
• Bloated clay
• Artificial cinders
• Expanded clay, slate, shale
• Coke breeze
• Expanded perlite
• Exfoliated vermiculite

Sintered fly ash (Pulverised fuel ash)

• The fly ash generally available from modern thermal power plants burning pulverised fuel is mixed with water and coal slurry in screw mixes and then fed onto rotating pans. Known as pelletizers, to form spherical pellets.
• The green pellets are then fed onto a sinter strand at a temperature of 1000° to 1200°C. The sintering process is similar to that used in the manufacture of portland cement.
• The fly ash may contain some unburnt coal which may vary from 2 to 15% depending upon the efficiency of burning. Due to sintering, the fly ash particles coagulate to form hard brick-like spherical particles. The produced material is screened and graded. In the UK, it is sold by the trade name ‘Lytag’.

Foamed slag

• Foamed slag is a by-product produced in the manufacture of pig iron. If the cooling of slag is done with large excess water, granulated slag is formed which is used in the manufacture of blast furnace slag cement.
• If the cooling of slag is done with a limited amount of water, in such a way as to trap steam in mass, it produces a porous, honeycombed material that resembles pumice.
• Sometimes, the molten slag is rapidly agitated with a limited amount of water and the steam and gas produced are made to get entrapped in the mass. Such a product is called foamed slag or expanded slag.

Bloated clay

• When the special grade of clay and shales are heated to the point of incipient fusion, there will be expanded due to the formation of gas within the mass. The expansion is known as bloating and the product so formed is used as lightweight aggregate.
• The CBRI has constructed an experimental building using bloated clay as lightweight aggregate and it has been performing well.

Exfoliated vermiculite

• The raw vermiculite material resembles mica in appearance and consists of thin flat. flakes containing microscopic particles of water. On heating with a certain percentage of water, it expands by delamination in the same way as that of slate or shale. This type of expansion is known as exfoliation.
• The expansion of vermiculite may be 20 to 30 times its original volume, with a density of Only 60 to 130 kg/m3. Hence, the concrete made with vermiculite as aggregate will have very low density and Very low strength.
• Concrete with vermiculite aggregates is used for heat, insulating, and sound insulation. Manufacture of blocks etc. The vermiculite products can be cut, sawn, nailed, or screwed.

Cinders, clinkers, breeze

• The partly fused or sintered particles arising from the combustion of coal are termed cinder or clinker or breeze.
• Cinder aggregates undergo high drying shrinkage and moisture movement.
• These are used for making building blocks for partition walls, for making screeding over flat roofs, and for plastering purposes.

Also Read: What is Workability of concrete

Properties of Light Weight Aggregate Concrete

The Density of Light Weight Concrete

• The density of lightweight concrete varies between 300 kg to 1900 Kg/m³.
• For further decrease density as low as 300 Kg/m³ you can use expanded vermiculite or perlite.
• If you use sintered fly ash, expanded slag, bloated clay, etc then the density of concrete is about 1900 Kg/m³ can be produced.

Strength of Light Weight Aggregate Concrete

• Lightweight concrete strength varies between 0.3 Mpa to 40 Mpa.
• If you use higher cement content like 560 Kg/m³, you can achieve the strength of concrete of about 60 Mpa.
• Normally the cement content in lightweight concrete varies from the same as a normal aggregate  to two-thirds more for the same strength of concrete.

Absorption and Protection

• The nature of lightweight aggregate is high absorption and hence special care have to be taken to protect the reinforcement from corrosion.
• You can achieve this by either providing more minimum cover compare to ordinary concrete or by using coated reinforcement with 3 mm thick rich cement paste.
• The cement pastes are able to improve the bond strength and also prevent corrosion. The coating can be done very well by uniting.

Extra

• The chances of shrinkage crack are high because the lightweight aggregate concrete has a higher drying shrinkage and is coupled with its low tensile strength.
• The modulus of elasticity property of lightweight aggregate cement concrete is lower than that of normal ordinary concrete.
• The rate of achieving strength with time is similar to that of ordinary concrete cured under the same conditions. The bond strength is around 0.5 to 0.75 of that for ordinary concrete.
• Most of the lightweight aggregate except sintered fly ash and bloated clay are angular in shape and rough in texture. They produce a harsh mix. Workability can be improved by the addition of excess fine material, pozzolanic material or some plasticizing admixtures.

Also Read: What is Shrinkage of Concrete

FAQ 1: What is Properties of Light Weight Aggregate Concrete?

The Density of Light Weight Concrete The density of lightweight concrete varies between 300 kg to 1900 Kg/m3, Lightweight concrete strength varies between 0.3 Mpa to 40 Mpa,

FAQ 2: Type and use of Light Weight Aggregate Concrete?

a. Natural lightweight aggregate e.g 1. Pumice 2. Scoria 3. Rise husk 4. Sawdust 5. Diatomite 6. Volcanic tuff 7. Foamed lava b. Artificial high weight aggregate e.g. 1. Sintered fly ash, 2. Foamed slag, 3. Bloated clay, 4. Artificial cinders, 5. Expanded clay, slate, shale, 6. Coke breeze, 7. Expanded perlite, 8. Exfoliated vermiculite,

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