- Definition of Lightweight Concrete
- Advantages of Lightweight Concrete (LWC)
- Disadvantages of Lightweight Concrete (LWC)
- Types of Lightweight Concrete (LWC)
- Video on Lightweight Concrete
- Frequently Asked Questions
Definition of Lightweight Concrete
Generally, the density of conventional concrete is about 2200 to 2600 kg/m3. This heavy self-weight makes it uneconomical. The concrete, which is having a density ranging from 300 to 1850 kg/m3 can be called lightweight concrete. The density of concrete can be reduced by different methods like by replacing the normal aggregate with lightweight aggregates or by using cellular-porous aggregates or by introducing the air or gas bubbles in a mortar or by discarding part of its contents (sand fraction) with suitable lightweight material.
Advantages of Lightweight Concrete (LWC)
- Reduction in dead weight
- Less hauling and handling costs
- The important factor in design, particularly in the case of weak soil and tall structures is the dead weight of the structure. With the help of LWC, we can lower the dead weight/load.
- Usage of this LWC in floors and walls may further reduce the load on the foundation
- In the case of air conditioning to be installed, adopting LWC will be a significant advantage from the point of view of thermal comforts and lower power consumption.
- Acts as an outlet for industrial wastes like slag, fly ash, clinker, etc.’
Disadvantages of Lightweight Concrete (LWC)
- Because of its weightlessness, few practitioners may tend to have the tendency to think like it may not possess the strength as conventional concrete.
- Lightweight concrete being comparatively porous, when used for reinforced concrete, reinforcement may become prone to corrosion. The additional coating on reinforcement with an anti-corrosive compound, in turn, increases the cost.
Also read: What is Concrete and Types of Concrete?
Types of Lightweight Concrete (LWC)
- Lightweight aggregate concrete
- Structured lightweight concrete
- Aerated concrete
- No fines concrete
The above types are further classified as below:
|No-fines concrete||Light-weight aggregate concrete||Aerated Concrete|
|Chemical aerating||Foaming mixture|
Table 1: Groups of Light-weight Concrete
Note: Please rotate your phone to see the full table on your mobile
Light-weight aggregate concrete (LWAC)
It is usually produced using lightweight aggregates. Different light-weight aggregates produce different densities of concrete. Strength and Density ranges that can be produced with LWAC are respectively 0.3 MPa to 40 MPa and 300 to 1900. The cement content usage ranges from 200 to 500.
The density of lightweight concrete decides its strength. Non-porous aggregates with heavyweight can produce stronger concrete with higher cement content. Also, strength depends on the grading of aggregate, the water-cement ratio, and the degree of compaction, and the type of fine aggregates.
|#||Type of Concretes||Bulk Density of aggregates (Kg/m³)||Dry density (Kg/m³)||Compressive strength (28 days)||Drying shrinkage 10-⁶||Thermal Conductivity
|1||Sintered fly ash:
|2||Sintered fly ash with natural sand Coarse||800
Table 2: Typical properties of Common Light-weight Concretes
Structured lightweight concrete
This form of concrete is gradually becoming one of the most essential concrete construction materials. Lightweight concrete that has the same strength as ordinary concrete will have an unquestionable economic advantage. Concrete with a 28-day compressive strength of more than 17 MPa and a 28-day dried unit weight of less than 1850 is referred to as structured lightweight concrete. Lightweight aggregates or a combination of conventional and lightweight aggregates are used in this type of concrete.
Natural sand is a common fine aggregate, and lightweight aggregate has a maximum size of 19 mm. Such lightweight concrete can be termed as ‘sanded lightweight concrete.’ To avoid the ‘floating of aggregate and mortar falls down’ in case of a high slump and over vibration, the maximum slump employed in the case floor or deck slab is 100 mm. The fire resistance of lightweight concrete constructed with slag, pumice, or brickbats as aggregate is higher.
The fire resistance of lightweight aggregate concrete is higher than that of regular concrete. Trial mixes are commonly used to develop a lightweight concrete mix design.
With different types of aggregates, the mixing technique for lightweight concretes may differ. For structural light-weight concrete, it is normal practice to mix the aggregate with roughly 2/3 of the mixing water for up to one minute before adding the cement and the remaining mixing water.
Continuous mixing is done as needed for homogeneity. To achieve a homogeneous mix, it usually takes 2 or more minutes. To reduce degradation, the aggregate is added towards the end of the mixing process in some insulating concrete.
When air or gas is introduced into a slurry of Portland cement or lime with finely crushed siliceous filler, the outcome is an equally cellular structure when the mix sets and hardens which is called Aerated concrete. Even though it is called aerated concrete, it is not concrete in the typical sense.
It’s composed of water, cement, and finely crushed sand, as previously stated. Gas concrete, foam concrete, and cellular concrete are all terms used to describe aerated concrete. The density of aerated concrete ranges from 300 kg/m3 to around 800 kg/m3.
Aerated concrete can be made in a number of different methods:
- During the liquid or plastic stage, a chemical process within the bulk produces gas.
- By combining the slurry with the prepared stable foam.
- By incorporating finely powdered metal (typically aluminum powder) into the slurry and causing it to react with the calcium hydroxide freed during the hydration process, a considerable amount of hydrogen gas is produced. The cellular structure is created when hydrogen gas is present in the slurry mix.
Also check: Aerated Autoclaved Concrete PPT
Applications of Aerated concrete
The application of foam concrete has grown in popularity not just due to its low density, but also due to its other features, particularly its ability to provide thermal insulation. Lower density grades are used for insulation, whereas medium-density grades are utilized to make building blocks or load-bearing walls, and higher density grades are used to produce prefabricated structural components with steel reinforcement.
The third way to make light concrete is to leave the fines out of regular concrete. The term “no-fines concrete” refers to a type of concrete in which the fine aggregate fraction has been removed. Only coarse aggregate, cement, and water are used to make this concrete. Frequently, only a single-sized coarse aggregate with a size passing through 20 mm and retaining a thickness of 10 mm is employed.
Because of some of the advantages (The coefficient of thermal conductivity and drying shrinkage of no-fines concrete are indeed considerably lower than that of the traditional concrete.), it has over normal concrete, no-fines concrete is gaining popularity. “The single-sized aggregates make excellent no-fines concrete, which has large voids and hence is light in weight, as well as an architecturally great look.”
Application of No-fines Concrete
- No-fines concrete can be utilized for a range of projects. It’s widely utilized for load-bearing cast-in-situ external walls on single- and multi-story buildings.
- Because of its low initial cost and simplicity of breaking and reusing as aggregate, this type of concrete has been employed for temporary buildings. Architects consider this to be a beautiful building material.
- It can be used for heat insulation on external walls because of its somewhat better thermal insulating property.
- It provides a suitable base for plastering because of the rough texture. Even if the outside of the no-fines concrete wall is battered by rain, the inside of the wall remains dry.
- It provides a good base for plastering due to the rough texture. Even if the outside surface of the no-fines concrete wall is beaten by rain, the inside of the wall will remain dry due to minimal capillary action caused by the huge spaces.
- No-fines concrete should become a popular construction material in areas where sand is scarce.
Also Read: Complete Guide on Grades of Concrete
Video on Lightweight Concrete
Frequently Asked Questions
How to make concrete planters lightweight and durable?
Materials required: Pearlite, Peat moss, and Quick setting cement.
Procedure: Take equal amounts of all ingredients mentioned in bowls and mix them in a separate large bowl. Slowly add water to it. Thoroughly mix them till it appears as a homogeneous mix. Apply it on a ‘plastic disposable bowl’ with sufficient thickness to make a Lightweight concrete planter. It takes a maximum of 1 week for it to dry. After 1 week we can use them as a concrete planter.
How to make lightweight concrete blocks?
Materials required: Cement, Lightweight Aggregates, Sand, and Water.
Procedure: Prepare the materials as per the proportions recommended. Then, mix them on a suitable base or leveled ground and add water while mixing. Make sure that homogeneity in the mixture appears. Pour the homogeneous mixture into prepared standard-size moulds and let them be in the moulds for 24 hours. Cure them for a recommended time, usually, it takes a long time for the concrete to properly cure. After the concrete has properly cured, the blocks are ready to use. For detailed procedures on how the light concrete blocks are made, watch the below video.