Tag Archives: Building materials

aggregate, Building materials

Lightweight Aggregate: Manufacturing, Properties and Types

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Lightweight aggregate plays a vital role in modern construction by reducing structural dead load while maintaining strength and durability. Widely used in lightweight aggregate concrete, it improves thermal insulation, seismic performance, and material efficiency. Understanding the types of lightweight aggregate—both natural and artificial lightweight aggregate—helps engineers select suitable materials for specific applications. Equally important is the lightweight aggregate manufacturing process, which influences density, strength, and absorption characteristics. The properties of lightweight aggregate, such as low unit weight, porosity, and adequate compressive strength, make it ideal for structural, geotechnical, and precast works. This article explains how manufacturers produce lightweight aggregates, highlights their key properties, and describes the different types available, providing a clear technical foundation for effective design and construction decisions.

Lightweight aggregate is a widely used construction material owing to its versatile properties. In this blog, I will walk you through what is a lightweight aggregate, its properties, applications and manufacturing process.

  1. What is a lightweight aggregate?
  2. Features of Lightweight Aggregates
  3. Lightweight Aggregate Desired Characteristics
  4. Types of Lightweight Aggregates
  5. Lightweight Aggregates Manufacturing Process
    1. Extraction or quarrying 
    2. Sizing 
    3. Reaction
    4. Cooling
  6. Lightweight Aggregate Applications
  7. Key takeaways
  8. Conclusion

What is a lightweight aggregate?

Lightweight aggregate is a coarse aggregate used to make lightweight concrete for structural as well as non-structural applications.

  • The Compressive design strength of normal concrete for cast-in-situ, precast and prestressed concrete ranges between 20 N/mm2 to 35 N/mm2. On the other hand, the minimum compressive design strength of concrete which uses lightweight aggregate will be around 17-18 N/mm2.
  • Normal concrete has a density between 2300 and 2500 kg/m3. However, when it comes to LWC the density ranges between 500 kg/m3 to 1800 kg/m3 depending on the type of aggregate used.
  • Lightweight concrete with densities lower than 17 N/mm2 falls under the category of LWC. And, those with densities above 17 N/mm2 are referred to as structural lightweight concrete (SLWC).
  • LWC can also be designed for the minimum compressive strength as normal concrete by varying the proportions of mineral admixtures used.
  • SLWC is used for structural applications. They can be used along with reinforcement steel just like normal concrete.
A conveyor belt discharging material, possibly sand or gravel, from a height onto a pile beneath against a clear blue sky.
A machine dispensing lightweight aggregate during the manufacturing process for construction materials.

Features of Lightweight Aggregates

  • The lightweight aggregate used in concrete may have any form, including cubical, rounded, angular, and other shapes. Its workability is directly influenced by its form and texture.
  • These aggregates are known for absorbing little water and maintaining their low density. 
  • A high saturation level makes it an attractive option.
  • LWA can reduce the dead loads on the structure and make it more economical.
  • Has relatively low thermal conductivity and is preferred for roof insulations.
  • Helps in consuming industrial wastes like blast furnace slag, fly ash, clinkers etc.
  • Possess good acoustic properties.

In the next section we will see what are the desired characteristics of a lightweight aggregate.

Close-up of a pile of grey, textured gravel or crushed stone.
Close-up view of lightweight aggregate, essential for reducing structural dead load in modern construction.

Also read : Pervious Concrete- All Factors Affecting, Limitations & Methodology Explained

Lightweight Aggregate Desired Characteristics

  • The properties and composition should be consistent.
  • To ensure worthwhile structural savings, the aggregate should have a low specific weight, in compliance with the required ASTM requirements. 
  • The aggregate should have a low number of large external voids. And a high number of smaller well-distributed voids within the particles. 
  • Individual aggregate particles should be able to withstand handling and mixing. 
  • The particles should have a good bond with the cement and should not react chemically with it. 
  • The aggregate should be rated appropriately for the intended use, according to the relevant ASTM specification 

Types of Lightweight Aggregates

Lightweight Aggregates can be divided into three types by their sources:

A chart illustrating the classification of lightweight aggregates, divided into natural aggregates from volcanic origin, such as pumice, scoria, and diatomite, and processed/artificial aggregates like expanded clay/shale, perlite, exfoliated vermiculite, and sintered fly ash. Key properties include low bulk density, high porosity, and good thermal insulation.
A visual classification of lightweight aggregates, showcasing natural aggregates like pumice and scoria alongside processed aggregates such as expanded clay, perlite, and sintered fly ash, emphasizing their low bulk density and high porosity.

(1)Industrial waste lightweight aggregate – This is processed by industrial wastes, such as fly as, ceramisite, expanded slag ball, cinder and light sand, etc.

(2)Natural aggregate – This is made from natural porous stone, such as pumice, volcanic cinder, and light sand, etc.

(3) Artificial lightweight aggregate – This is manufactured from local materials, such as clay ceramisite, and expanded perlite, etc.

Also read : ALC Panel – Autoclaved lightweight Concrete Panel

Lightweight Aggregates Manufacturing Process

The majority of lightweight aggregate is made from clay, shale, or slate. However, furnace slag, natural pumice, vermiculite, and perlite can all be substituted. 

The raw material (excluding pumice) is extended to about twice its original volume to create lightweight aggregate. The expanded material has properties that are similar to natural aggregate. As a result, it produces a lighter concrete product.

Let me show you the detailed procedure.

Extraction or quarrying 

Cone crushers, jaw crushers, hammer mills, and pug mills are used to crush the material, which is then screened for quality.

Sizing 

The material that passes through the screens is returned to the crushers, and the material that passes through the screens is recycled.

It is then moved to hoppers.

Reaction

  • The material is fed from the hoppers into a rotary kiln. 
  • It is heated to about 1200°C (2200°F) using coal, coke, natural gas, or fuel oil. 
  • When the raw materials are heated, carbonaceous compounds in the material liquefy, forming gas bubbles that expand the material.
  • In addition, VOCs (volatile organic compounds) are released during the process.
  • The enlarged product emerges from the kiln.

Cooling

  • The product clinker is conveyed into the clinker cooler, where it is cooled by air and shaped into a porous material. 
  • The lightweight aggregate is screened for scale, crushed if necessary, and stockpiled after cooling. 
  • Rotary kilns are used by the vast majority of plants (roughly 90%). However, travelling grates are also used to heat the raw material. 

Lightweight Aggregate Applications

Close-up of a block of lightweight aggregate concrete displaying various aggregate particles, featuring a caption highlighting its key properties such as reduced dead load, improved insulation, and fire resistance.
Lightweight aggregate concrete block showcasing its unique porous structure and key properties: reduced dead load, enhanced insulation, and improved fire resistance.
  1. Screeds and thickening are made with lightweight aggregates. When the floor or roofs need thickening or smoothing, it can be used to easily achieve it.
  2. Can be applied to screeds and walls where the wood would be nailed together.
  3. Casting structural steel in lightweight aggregate concrete can protect it from fire and corrosion. Also, it can be used to cover architectural needs.
  4. Can be used on roofs as a heat insulation material.
  5. Used as insulation for water pipes.
  6. Used to construct partition walls and panel walls in frame structures.

That’s it about lightweight aggregates. Hope you found this article insightful. Let us know in the comments.

Key takeaways

  • Lightweight aggregates reduce structural dead load without compromising essential strength.
  • Manufacturing methods strongly influence density, strength, and absorption properties.
  • Natural, industrial by-product, and artificial types offer flexibility in material selection.
  • These aggregates improve workability and enable efficient construction practices.
  • They support structural, insulation, fire protection, and architectural applications.
  • Proper processing ensures consistent quality and performance.
  • LWA contribute to durable, economical, and sustainable construction solutions.

Conclusion

In conclusion, lightweight aggregates offer an efficient solution for modern construction by balancing strength, weight reduction, and performance. Their role in lightweight aggregate concrete has become increasingly important for structural and non-structural applications alike. Understanding the types of lightweight aggregate, including natural and artificial allows engineers to select materials suited to specific design needs. The lightweight aggregate manufacturing process directly affects quality, durability, and consistency, making process control essential. In addition, the properties of lightweight aggregate, such as low density, thermal insulation, and adequate strength, contribute to improved structural efficiency and sustainability. When selected and applied correctly, these materials support safe design, cost-effective construction, and long-term performance across a wide range of engine

aggregate, Building materials

Specific Gravity and Water absorption test on Aggregate

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Specific gravity and water absorption test are significant tests on aggregates. Perhaps aggregates are the fundamental and essential components of concrete and play a significant role in the design mix of concrete. More than 70 to 80 per cent of the volume of concrete is aggregate. Hence the water absorption and specific gravity test are essential and significant tests .

The specific gravity test of aggregates is a crucial procedure in construction and materials engineering. This test measures the density of aggregates, which helps decide their quality and suitability for construction. Specifically, the specific gravity for coarse aggregate is essential for mix design and ensuring structural stability. Additionally, the specific gravity test of aggregate provides valuable data for comparing different materials. Alongside this, the water absorption test is vital. It measures how much water aggregates absorb, which affects their performance in concrete. The water absorption formula calculates the amount of water absorbed relative to the aggregate’s weight. Both the specific gravity and water absorption tests are critical. These tests assess aggregate properties and ensure the durability of construction materials.

The specific gravity is the measure of strength of aggregates, while water absorption indicates the porosity of aggregates.

  1. Specific Gravity Tests on Aggregates
  2. Specific gravity test on aggregates
  3. Water absorption test on aggregates
  4. Specific gravity test on aggregates
    1. Relevant IS code:
    2. Apparatus used:
    3. Test procedure of Specific gravity test of aggregates
    4. Water absorption test of aggregates – Test procedure
  5. Key Takeaways
  6. Conclusion

Specific Gravity Tests on Aggregates

Aggregates are the second major ingredient of concrete that contributes around 60 to 70% of its volume. One of the major contributing factors to the concrete quality is the quality of aggregates used therein. The test methods of aggregates are done as per IS 2386 part-4 assists in assessing the quality of aggregates. Following are the tests for analyzing the quality of aggregate.

Construction site showing a concrete batching plant with aggregates piled on the ground.
A modern aggregate processing facility with various types of aggregates ready for concrete production.

This article is about Specific Gravity and Water absorption test on Aggregate.

Also Read : Quality tests to be done on Concrete

Also Read : Bitumen – 9 quality tests on bitumen

Specific gravity test on aggregates

The specific gravity test of aggregate is crucial for assessing the density and quality of aggregates used in construction. This test evaluates the ratio of the weight of the aggregate to the weight of an equal volume of water. It is essential for both fine and coarse aggregates, providing insights into their suitability for various applications. The specific gravity for coarse aggregate, in particular, impacts the mix design and overall performance of concrete. Precise results from the specific gravity test of aggregates help guarantee that the concrete achieves the desired strength and durability. Proper understanding of these tests is vital for effective construction practices.

The specific gravity is an indirect measure of the strength of aggregate. Through this test, the general identification of the aggregate becomes easier. Low specific gravity aggregates are weak. Hence, they are not suitable for construction. 

Specific gravity and water absorption test on aggregate.
Close-up view of aggregates used in construction, highlighting their essential role in concrete mix design.

Water absorption test on aggregates

The water absorption test on aggregates measures how much water an aggregate can absorb. This impacts the strength and durability of concrete. This test is crucial for determining the porosity of the aggregate and its ability to retain moisture. To conduct the water absorption test, aggregates are first weighed dry and then submerged in water until they reach saturation. The water absorption formula calculates the percentage of water absorbed by comparing the saturated weight to the dry weight. Accurate water absorption test results ensure proper mix design. They also predict concrete performance. This makes it a key factor in construction quality control.

Water absorption of aggregate measures the weather resistance. It is the percentage of water the aggregate absorbs when immersed in water. The test method for specific gravity and water absorption test is as follows.

Specific gravity test on aggregates

Relevant IS code:

  • IS:2386(Part 4)-1963

Apparatus used:

  • Weighing machine
  • Drying oven 
  • Wire mesh
  • Container
Specific gravity and water absorption testing apparatus
Apparatus for conducting the specific gravity and water absorption tests on aggregates, essential for evaluating the quality of construction materials.

Test procedure of Specific gravity test of aggregates

  • For this test, take about 2000g of aggregate and wash them thoroughly with water.
  • Remove the fine particles and dust, then drain the water and place them in the wire basket.
  • Then immerse this in distilled water with a temperature between 22 and 32 degree Celsius for 24 hours.
  • Then Weigh the basket with aggregates and record them as A1.
  • After 24 hours, remove the aggregates from the mesh and weigh them as A2.
  • Then drain the water from the aggregate and Again weigh the dried aggregate. B
  • Place the sample in the dry oven for 24 hours. after the oven drying weighs them and record as C.
  • Now calculate the specific gravity and water absorption of the aggregate using the given formula.

Specific gravity = C / (B- A)

Water absorption = {(B-C)/C} * 100

where, A= A1 – A2, ie weight of the saturated aggregate in water

B = weight of drained aggregate 

C = weight of oven-dried aggregate.

Aggregate with high specific gravity has good strength. The normal value of specific gravity is 2.5 to 3.0. The water absorption should not exceed 0.6%. Thus this test helps to determine the quality, strength and water absorption.

Water absorption test of aggregates – Test procedure

The procedure is same as specific gravity of aggregates. The water absorption should not exceed 0.6%. Thus this test helps to find the quality, strength and water absorption.

Key Takeaways

The specific gravity test of aggregate is essential in determining the strength and quality of aggregates. It provides critical information for construction mix designs and ensures structural stability. Specifically, the specific gravity for coarse aggregate influences the mix design and overall concrete performance. The water absorption test evaluates how much water an aggregate absorbs, affecting its durability. The water absorption formula helps calculate the water retained by aggregates, influencing mix design accuracy. Both the specific gravity test of aggregate and the water absorption test are vital in assessing aggregate properties. They guarantee that materials meet the required standards for construction durability.

Conclusion

The specific gravity test of aggregate is critical in determining the quality of aggregates in construction. The water absorption test is also crucial for assessing the suitability of aggregates. The specific gravity for coarse aggregate is a key parameter for concrete mix design, ensuring strength and structural integrity. Precise testing of specific gravity of aggregates helps predict performance and durability. On the other hand, the water absorption test assesses the porosity of aggregates. The water absorption formula determines the percentage of water absorbed. These tests are crucial for ensuring that aggregates meet the required standards. They give essential data for achieving high-quality, durable concrete structures.