Lightweight Concrete: A Step-by-Step Guide

What Is LightWeight Concrete?

Lightweight concrete has a lower density than conventional concrete. It is made by mixing lightweight aggregates. such as expanded clay, shale, or perlite, with cement, water, and sometimes other additives. It has thermal insulation properties and reduces the carbon footprint due to the use of less cement.

Generally, the weight of concrete has 137 lb/ft³ to 150 lb/ft³(2200 to 2400 kg/m³). Lightweight concrete has a weight of 25 lb/ft³ to 125 lb/ft³ (400 kg/m³ to 2000 kg/m³). The Deadweight of ordinary concrete is an uneconomical structural material.

A dead load of light concrete is much less than that of ordinary concrete. Light Weight Concrete can be created by adding lightweight aggregates. Light Weight Concrete can also be created by entering the air in normal concrete.

Benefits of Lightweight Concrete

1. Density

The density of lightweight concrete is 200 kg/m³ to 1500 kg/m³. Where low-density concrete is to be used, lightweight concrete is used for thermal insulation. High-density lightweight concrete can be made in a building like a slab, or column.

2. Tensile Strength

The tensile strength of lightweight concrete is about 15 to 20% of the compressive strength.

3. Compressive Strength

As the density of lightweight concrete increases, so does its compressive strength. The compressive strength of lightweight concrete is 0.5 to 35 N/mm².

4. Thermal Insulation

The thermal insulation of lightweight concrete is 5 to 6% higher than brick and 8 to 10% higher than concrete.

5. Fire Resistance

Light-weight concrete has good fire resistance. So it is used in buildings.

6. Durability

Light-weight concrete has a very porosity. So it does not protect the steel in the column.

7. Repairability

Light-weight concrete is soft, so it can be broken quickly. It can be easily repaired.

Type of Lightweight Concrete

 

Lightweight concrete can be obtained in three ways

• Lightweight aggregate concrete.
• Aerated concrete.
• No fines concrete.

1. Lightweight Aggregate Concrete

This concrete is made using lightweight aggregate instead of the aggregate used in ordinary concrete. There are two types of different lightweight aggregates.

A. Natural lightweight aggregates include pumice, diatomite, scoria, rise husk, sawdust, and volcanic cinders.

• Pumice

These volcanic rocks are light in weight and strong, which can be used in lightweight concrete. Pumice has also been used as one of the most lightweight Roman structures.

• Diatomite

Diatoms are obtained from the remains of microscopic aquatic plants. It is a good workability agent and also has good pozzolanic material. diatomite is also known as kieselguhr.

• Scoria

It is less strong than pumice. scoria is also a lightweight aggregate of volcanic origin which is usually dark.

• Rice Husk

Rice powder is used as a lightweight aggregate in lightweight concrete

• Saw Dust

Sawdust is used in lightweight concrete for flooring and lightweight element.

B. Artificial lightweight aggregates include bloated clay, Expanded shale, sintered fly ash, artificial cinders, and foamed slag.

• Sintered Fly Ash

Sintered fly ash is used to make Portland cement and also to make hard bricks

Special care should be taken while mixing lightweight aggregate as it is likely to disintegrate. Natural sand is added to increase the strength of lightweight concrete and to improve workability.

lightweight aggregate absorbs water. The coating can be done with a silicone compound to prevent water absorption. Covering the footing and slab can prevent corrosion of the reinforcement.

2. Aerated Concrete

This type of concrete is made by inserting gas bubbles into normal concrete.

Aerated concrete is known by various other names. Other names for aerated concrete are known as Siporex, Celecrete, vayuthan.

Aerated concrete is made differently.

1. Aerated concrete can be made by producing gas through a chemical process in concrete.
2. Aerated concrete can be made by adding foam to the concrete.
3. Aerated concrete can be made by adding metal powder to the concrete.

Aerated concrete can be made by producing gas by adding hydrogen peroxide and bleaching powder for chemical processing.

Aluminum powder is used as a metal powder which is 0.2% of the weight of cement.

3. No Fines Concrete

Small aggregates are not used in this concrete. Only coarse aggregate is used. Aggregates smaller than 12 mm are not used.

No fine concrete uses aggregate passing on a 20 mm sieve and stopping at a 10 mm sieve.

If the normal aggregate is used in no fine concrete, its density is 1600 kg/m³. If the lightweight aggregate is used, its density is 400 kg/m³ to 2000 kg/m³.

No fine concrete has an aggregate/cement ratio of 2: 1. The strength of concrete depends on its density aggregates/cement ratio, water/cement ratio.

The bond stress of no fine concrete can be achieved from 1.5 to 15 N/mm². It is not used in R.C.C due to low bond stress.

Uses of Lightweight Concrete

 

1. Light-weight concrete is used for temporary construction.
2. Light-weight concrete is used to build a labour colony on the site.
3. Light-weight concrete can be easily broken, so repairing can be done easily.
4. Light-weight concrete can be used in the elevation of a building.
5. Lightweight concrete has good heat tolerance, so it can be used where an air conditioner is to be used.
6. As the weight of the building decreases, the depth of the foundation can be increased, and its section can be made smaller.
7. In lightweight concrete, clinkers, fleece ash use, and other materials can be used.
8. Lightweight concrete has good fire resistance, so if used in a building, it is protected from the effects of fire.
9. Use lightweight concrete in small sections such as partition walls,
10. The use of lightweight concrete in precast units has increased.

Advantages & Disadvantages of Lightweight Concrete

Advantages of Lightweight Concrete

1. As the weight of the building decreases, the depth of the foundation can be decreased, and its section can be made smaller.
2. As lightweight concrete is light in weight, shuttering work has to bear less load.
3. Being lightweight aggregate speeds up construction and reduces transposition costs.
4. It is possible to nail in lightweight concrete.
5. Lightweight concrete can be used in thermal insulation.
6. Light-weight concrete can be easily broken, so repairing can be done easily.
7. Light-weight concrete has good fire resistance.

Disadvantages of Lightweight Concrete

Light-weight concrete has high porosity, so there is a risk of corrosion of reinforcement.

No fine concrete can not be used in RCC work as its bond stress is very low.

Durability of  Lightweight Concrete

Lightweight concrete does not protect against chemical reactions due to its porosity-like properties. It should not be used in heavy structures. It is not advisable to use lightweight concrete in marine structures, dockyards.