The concrete has a 28-day compressive strength of more than 17 MPa and an air-dried piece weight of no more than 1850 kg / m³.
Lightweight concrete Similar to normal concrete, except with light aggregates or a combination of light and normal weight aggregates. All lightweight concretes use both light, coarse, and light fine aggregates, standard lightweight concretes use natural sand instead of light, fine aggregates
If the mortar has a bulk density of less than 15 KN / m3, it is called a light mortar. Light mortar is made by mixing lime or cement as a binding agent, sand and sawdust, rice hulls, jute fibers, coirs, or fibers. of asbestos. Ash mortar is a variety of light mortars Light mortar is usually used in sound and heat-resistant construction Strength-based (ASTM C 270)
- Lightweight concrete is a special type of concrete that is lighter than conventional concrete.
- The density of this concrete is considerably low compared to normal concrete (2200 kg / m3 to 2600 kg / m3) (300 kg / m3 to 1850 kg / m3).
- A single method of making the concrete light, that is, by trapping air into the concrete. This is achieved in different ways in practice:
- i) Replacing the usual aggregates with pore pores or LWA
- ii) Introducing gas or bubbles into the aerated concrete with mortar
- iii) Dispensing with the sand content of the concrete
- Without fines Concrete with light aggregates – Kingdom of UK, France, and the USA
- Aerated concrete – Scandinavian countries
- No – fine concrete is less popular
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Types Of Lightweight Concrete
The lightweight concrete box is also classified according to its intended use, e.g.
1. Structural lightweight concrete
2. Non-load bearing concrete
3. Insulating concrete
Lightweight aggregate concrete
- There are basically two types of lightweight aggregates.
- Natural aggregates
- Artificial aggregates
- Natural lightweight aggregates are less preferred than artificial aggregates.
- The aggregates determine the density of the concrete. A concrete density of only 300 kg / m3 can be achieved. The compressive strength ranges from 0.3 MPa to 40 MPa.
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Natural Lightweight Aggregate
They do not have uniform quality and cannot be found in many countries. As such, they are not universally used for the manufacture of lightweight concrete. Of all natural lightweight aggregates, only pumice stone is widely used.
- Foam slag – was the first lightweight Aggregate suitable for reinforced concrete. (Which was manufactured in large quantities in (UK).
- Sintered powder – a fuel ash device used for various structural purposes and marketed in the UK and sold under the trade names
- Expanded Tone and Slate – capable of being strong enough for Prestressed concrete
- pumice stone – used for reinforced concrete roof panels, are mainly for industrial roofs
Artificial Lightweight Aggregate
Artificial aggregates are classified according to the raw material used and the manufacturing method.
i. The aggregates classified according to the raw material are those that are produced by the application of heat. They are in order as expanded clay, slate, slate, diatom slate, perlite, obsidian, and vermiculite.
ii. The second category of aggregates is produced by the special cooling process, through which an expansion of the blasting slag is obtained.
- Cinder, Clinker, and breeze
- Foamed slag
- Bloated clay
- Pulverized fuel ash
- Expanded perlite
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Lightweight Aggregate Concrete
Very often lightweight concrete is made using lightweight aggregates, in general, different Lightweight Concrete has different densities because the density of the concrete differs in various properties such as bulk density, dry density, compressive strength, shrinkage, and thermal conductivity.
Most lightweight aggregates have rapid absorption, which is one of the difficulties in the normal mixed design method for lightweight concrete.
However, it is possible to seal the Lightweight Aggregate with a bitumen coating. Coating the aggregate with bitumen can reduce the adhesive strength between aggregate and paste, which leads to a certain compressive strength of the concrete
Structural Lightweight Concrete
Structural lightweight concrete will be one of the most important building materials. Concrete, which is light and strong enough to be used in conjunction with steel reinforcement, is a cheaper material than traditional concrete. Concrete with a 28-day compressive strength of more than 17 MPa and a 28-day air-dried unit weight of not more than 1850 kg / m3 For practical reasons, it is common to use normal sand as fine and coarse aggregate lightweight concrete with a maximum size of 19 mm as lightweight concrete is called standard lightweight concrete. Lightweight concrete
Workability of Lightweight Concrete
If there is a high degree of a slump and strong vibrations, the mortar sags and the aggregates tend to float. Lightweight concrete has a stronger moisture movement than normal concrete The greater drying shrinkage with lower tensile strength means that lightweight concrete has shrinkage cracks, but the higher elasticity and the lower modulus of elasticity help tensile cracks to reduce Since lightweight concrete contains a high proportion of air, it is, of course, a better material in terms of
a) sound absorption
b) sound insulation
c) heat insulation
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Mix Design Of Lightweight Concrete
- Due to the variable absorption of water by the aggregates, it is difficult to determine the water-cement ratio.
- The lack of an accurate value for absorption, specific gravity, and content of free moisture in the aggregate makes it difficult to apply the water-cement ratio for the mixing ratio precisely.
- Test mix The density of concrete made from saturated aggregates is higher, and the durability of this concrete, especially its frost resistance, is lower.
- Concrete with saturated aggregates has a higher density, which has a negative effect on freezing and thawing.
- The aggregates are coated with bitumen to overcome the problem of water absorption.
Mixing Process Of Lightweight Concrete
The mixing process for lightweight concrete can vary depending on the type of aggregate. The general practice for lightweight concrete is to mix the aggregate and about 2/3 of the mixed water up to a minute before adding cement and rocking. Water mixture.
Advantages Of Lightweight Concrete
- Reduces the dead weight of the building
- Easy to handle and thus reduces transport and handling costs
- Improve processability
- Relatively low thermal conductivity
- Comparatively more durable, but less abrasion-resistant
- Use in prestressed concrete, high-rise buildings, and shell roofs
- Good frost resistance and thawing effect compared to conventional concrete
- Help to remove industrial waste such as Fly ash, clinker, slag, etc.
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