WHAT IS LIGHT WEIGHT CONCRETE - TYPES, USES AND ADVANTAGES

Light Weight Concrete

Light weight concrete is a mixture of lightweight coarse aggregate and sometimes a portion or entire fine aggregates.A structure light weight concrete mix has a density of about 105 pound per cubic foot.The light weight concrete density is less because of light weight coarse aggregates and sometimes light weight fine aggregates are used, which make the concrete weight less.

The light weight aggregate used are usually expanded shale, clay or slate materials that have been fired in a rotary kiln to give them a porous structure, similar to volcanic rock.In some mixes air cooled blast furnace slag is also used.

Structure light weight concrete mixes can be designed to achieve similar compressive strength as normal weight concrete.They also have the same durability and mechanical characteristics as regular weight concrete.There are other classes of non-structural light weight concrete with lower density made with other aggregate materials and higher air voids in the cement paste matrix such as in cellular concrete.

Types of Light Weight Concrete

1. Lightweight Aggregate Concrete
2. Aerated Aggregate Concrete
3. No Fines Concrete

1. Lightweight Aggregate Concrete

Light weight aggregate concrete can be produced using a variety of lightweight aggregates.In early 1950s the use of lightweight concrete blocks was accepted in the UK for load bearing inner leaf of cavity walls.

 The following are the types of light weight aggregate concrete:

• Formed Slag: It was the first light weight aggregate suitable for reinforced concrete that was produced in large quantity in the UK.

• Pumice: It is used for reinforced concrete roof slab, mainly for industrial roofs in Germany.

• Expanded Clays and Shales: It is capable of achieving sufficiently high strength for prestressed concrete.Well established under the trade name of Aglite and Leca (UK), Haydite, Rocklite, Gravelite and Aglite (USA).

2. Aerated Concrete

Aerated concrete has the lowest density, thermal conductivity and strength.Like timber it can be sawn, screwed and nailed but there are non-combustible.Aerated concrete is a lightweight, cellular material consisting of cement and sand or lime or other silicious material.It is made by either a physical or a chemical process during which either air or gas is introduced into a slurry which generally contains no course materials.

3. No Fines Concrete

No fines concrete may be defined as concrete mixtures containing little or no fine aggregates.The fine aggregate is not added in this concrete so that there are voids left in the coarse aggregate.The coarse aggregate may be any of the usual type or the light weight aggregate.The coarse aggregate used should be finer than 20 mm size and not more than 10% should pass the 10 mm sieve.Generally no fine concrete is produced with a cement aggregate ratio of 1:6 to 1:10, but practical mixes vary rather widely.The variation of cement aggregate ratio for lean mixes is from 1:10 to 1:20.The corresponding cement contents are 130 kg/m3 to 70 kg/m3.In case of fines concrete there is a narrow optimum value of w/c ratio for any given aggregate.

Although the strength of no-fine concrete is considerably lower than that of normal-weight concrete, this strength ,coupled with lower dead load of the structure, sufficient in building up to about 20 storeys high and in many other applications.

Properties of Light Weight Concrete

• It is light in weight because of fly ash as aggregate.
• Compressive strength varies from 0.3Mpa to 40Mpa.
• It has high thermal and acoustical insulating qualities.

Uses of Light Weight Concrete

• It is used in general insulation of walls.
• It is used in insulating water pipes.
• It is used in heat insulation on roofs.
• It is used for reinforced concrete.
• It is used for fixing bricks to receive nails from joinery.
• It is used in casting structure steel to protect its against fire and corrosion or as a covering for architectural purposes.

Advantages of  Light Weight Concrete

• Self compaction.
• Easy to transport.
• Reduced seismic forces.
• Improved constructability.
• Improved structural efficiency.
• It has low drying shrinkage.
• Pumping concrete to large distance.
• It has good sound insulation properties.
• Formwork will withstand low pressures.
• Reduced the dead load of a structure due to less density.
• It is eco-friendly as it used clinker, fly ash, slag etc.

Disadvantages of  Light Weight Concrete

• It is porous and shows poor resistance.
• Very sensitive with water content in the mixture.
• Cement mixtures have difficult in placing and finishing.
• Foam concrete mixtures is susceptible to water content in the mixture.
• Mixing time is longer than conventional concrete to assure proper mixing.