What Is Coarse Aggregate | Properties of Coarse Aggregate | Uses of Aggregates | Classification of the Aggregates | Aggregates Meaning

What Is Coarse Aggregate | Properties of Coarse Aggregate | Uses of Aggregates | Classification of the Aggregates | Aggregates Meaning18 min read

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What Is Coarse Aggregate?

Coarse aggregates are irregular in shape, broken stones, or naturally occurring round gravels that are used to make concrete. Coarse aggregates for structural concrete contain broken stones of hard rock like granite & limestone or river gravels.

What Is Coarse Aggregate | Requirements of Good Coarse Aggregates | Uses of Coarse Aggregates | Classification of the Aggregates
Coarse Aggregate

Concrete Mix is produced by many ingredients or components but mostly made up of a material called Coarse Aggregates and they are one of the essential components of concrete and occupy large volumes in the concrete mix.


Coarse Aggregate Meaning

Aggregate which has a size bigger than 4.75 mm or which retrained on 4.75 mm IS Sieve are known as Coarse aggregate.

Origin Of Aggregates

The aggregates are generally acquired by blasting in stone quarries or breaking them by hand or by crusher machines.

The aggregates manufactured by machine-crushed consist of stones of various sizes whereas hand-broken aggregates consist of only single size stones.

Materials that are larger to be retained on 4.75 mm sieve size are called coarse aggregate, and their maximum size can be up to 63 mm. In coarse aggregate, foreign material like coal, lignite, soft fragments, and clay lumps should not exceed 5 percent of their actual weight.

Read More: Flakiness and Elongation Index Test of Coarse Aggregate


Characteristics Requirements For Good Quality Coarse Aggregate

The aggregates which are utilized in the construction must possess and fulfill the following characteristics.

  • The coarse aggregate should be hard and strong enough to withstand the crushing action.
  • It should be clean and free from the coating of organic materials, clay, and dust otherwise it will reduce the bonding of the aggregate with concrete. 
  • The coarse aggregate should be durable. The aggregate should not react with any chemical agent of cement after mixing. It should contain coarse, angular, sharp, and hard particles.
  • The shape of the aggregate preferably is spherical or cubical. Aggregate should be chemically inert. The coarse aggregates should be from a hygroscopic slat.
  • Coarse aggregates should not absorb water by more than 5% of their actual weight. Coarse aggregates should not be porous and soft.
  • The size of its grains should be such that it passes through a 63 mm IS sieve and entirely retained on a 4.75 mm IS sieve.
  • It should be free from disintegrated pieces, alkalis, vegetable matter, etc. The coarse aggregates should not contain flaky and elongated pieces in mass.

Uses Of Coarse aggregates In Construction Work

What Is Coarse Aggregate | Requirements of Good Coarse Aggregates | Uses of Coarse Aggregates | Classification of the Aggregates
Use of Coarse Aggregate in Construction (Concrete)
  • In the construction industry, an aggregate is used for its economic factor and to reduce any cracks, and most importantly to provide strength to the structure.
  • Aggregate can be used in several ways in construction. Inroads and railways ballast the aggregates are used to resist the overall (static as well as dynamic) load, to distribute the load properly to the supporting ground, and to drain the water off the surface.
  • It influences the hardness, abrasion resistance, elastic modulus, and other properties of concrete to make it more durable, strong, and cheaper.
  • Other uses include fills, backfills, drainage, and filtration applications.
  • Aggregates are also used in the preparation of braking moisture under slabs & vapor barriers.
  • Also, they are used in base preparation for driveways and roadways.

The coarse aggregates are also utilized in water filtration and sewage treatment processes. The uses of aggregates can be summarized into the following three categories:

  • As a bearing material
  • As a filling material
  • As an infiltrating material

Uses Of Aggregate In Concrete

Aggregate is an essential component of concrete mix. The aggregates uses in concrete are as follows:

  • Increases the volume of concrete, thus reduces the cost, aggregates account for 60-75% of the volume of concrete and 79-85% weight of PPC.
  • To provide a rigid structure.
  • To reduce the shrinkage and cracking on the concrete surface.
  • Coarse aggregate is used in many structures and substructures built by concrete mix e.g. different elements of a building, bridges, foundations, etc.
  • The higher the aggregate size the lesser its surface area and the minimum binding material (cement) will be required, resulting in a lower cost of construction.
  • A mixture of coarse and fine aggregate is used in concrete to make it denser, harder and durable against atmospheric action.

Uses Of Aggregates In Roads

What Is Coarse Aggregate | Requirements of Good Coarse Aggregates | Uses of Coarse Aggregates | Classification of the Aggregates
Use of Aggregate in Road
  • Aggregates are used as the base, subbase, and surface of roads in several forms.
  • Stabilized by utilizing cementitious materials (blends of cement, fly ash, slag, lime).
  • Stabilized with bituminous materials (bitumen or tar).
  • Stabilized with other materials (resins, fibers, geo-synthetics).
  • Recycled aggregate.
  • On roads, it is also used to help distribute the load and assist in groundwater running off from the road surface.

Classification Of Coarse Aggregates

Classification of aggregates done on various parameters like shape, origin, texture, density, and grain size, etc.

A) Classification Of Aggregates Based On Shape

The shape of aggregates is one of the most effective ways of differentiating particles. The shape of your chosen aggregates will have a significant effect on the workability of the concrete. The different shape of aggregates are:

1. Rounded Aggregates

What Is Coarse Aggregate | Requirements of Good Coarse Aggregates | Uses of Coarse Aggregates | Classification of the Aggregates
Rounded Aggregates

The rounded aggregates are mostly available in the seashore or riverbank area. It provides high workability & fewer voids in the concrete mix

But mostly it was not recommended for highstrength concrete elements because of its poor interlocking properties. Primarily it is used in lintel and PCC concrete and also as a filler material.


2. Angular Aggregates

What Is Coarse Aggregate | Requirements of Good Coarse Aggregates | Uses of Coarse Aggregates | Classification of the Aggregates
Angular Aggregate

The Angular Aggregates are low in workability. But it is mostly suitable for high-strength concrete elements because of its angularity and it produces high strength.

Due to its angularity, it easily interconnects with other aggregates and fewer voids are forming in concrete.


3. Irregular Aggregates

The Irregular Aggregates will develop strength slightly lower than the angular aggregates. The irregular shapes of aggregates are formed due to friction between the aggregates.

The bondage between the aggregates is very low due to its irregular shape and it develops low workability in concrete.


4. Elongated Aggregates

In Elongated Aggregates, the length of the aggregates is higher than its width. It is having low compressive strength and is not recommended for concrete.

If we use the elongated aggregate in concrete, the voids ratio will become high compared to the other aggregates.


5. Flaky Aggregates

Flaky Aggregates are having a very light thickness, and they can easily crack.

Because of its lower workability, it is not used in concrete, and also it quickly gets broken due to its minor thickness.


6. Flaky & Elongated Aggregates

The Flaky and Elongated aggregates are having less thickness and high in length. It is also not preferred for concrete mix due to its lower compressive strength.


B) Classification of Aggregates Based on Grain Size

If you separate aggregates by size, there are two categories namely fine aggregates and coarse aggregates.

1. Fine Aggregates

The size of the Fine Aggregate is defined as 4.75 mm or smaller. That is aggregates that can be passed through IS sieve no.4, with a mesh size of 4.75 mm. fine aggregates include things such as sand, silt, and clay.

Machine-crushed stone & crushed gravel might also fall under this category. Typically, Fine aggregates are used to improve the workability of a concrete mix.


2. Coarse Aggregates

Coarse Aggregates measure above the 4.75 mm limit. These are more likely to be natural stone or gravel that has been crushed or processed.

These will reduce the amount of water needed for a concrete mix, which may also reduce workability but improve its inner strength.


C) Classification of aggregates based on Density

The aggregates are mainly classified into three categories according to density.

1. Lightweight Aggregates

What Is Coarse Aggregate | Requirements of Good Coarse Aggregates | Uses of Coarse Aggregates | Classification of the Aggregates
Light Weight aggregates

The Lightweight Aggregates will have a high absorption value compared to other aggregates. Thus the slump loss happening in lightweight concrete instantly due to the absorption.

The lightweight aggregates are used as a filling material in flooring, deck slab, and insulating the fire line pipes, etc. The density of lightweight aggregates is varied between 800 to 1100 kg/cum.

Read More: Specific Gravity and Water Absorption Test of Coarse Aggregate


2. Normal Weight Aggregates

The normal-weight aggregates are such as sand, gravel material, which are regularly used in construction.

The normal weight aggregates are utilized for column, beam & slab concrete. The density of normal weight aggregates is ranging between 1520 to 1680 kg/cum.


3. Heavy Weight Aggregates

The Heavyweight Aggregates are mostly used in construction to protect the radiation room.

The main drawback of heavy-weight aggregate is it produces very low workability in concrete. The density of heavy-weight aggregates ranges between 2100 to 2900 kg/cum.


D) Classification Of Aggregates Based On Geographical Origin

By the source of aggregates, it can be classified into two types, namely natural aggregates and manufactured aggregates.

1. Natural Aggregates

Natural aggregates are available in river banks, seashore, and pits mines. The natural aggregates can be utilized in construction work after involving some quality tests.

The river sand and gravel are an example of naturally available aggregates.


2. Manufactured Aggregates

What Is Coarse Aggregate | Requirements of Good Coarse Aggregates | Uses of Coarse Aggregates | Classification of the Aggregates
Manufractured Aggregates

All aggregates are developed from natural aggregates only. But the manufactured aggregates mean the natural aggregates are processed to produce new size and quality aggregates which are suitable for different construction activities.


Properties of Coarse Aggregates

There are some properties of characteristics of coarse aggregates which influence the properties of the resulting concrete mix.

The properties of the coarse aggregates are as follows,

  1. Composition
  2. Size and Shape
  3. Surface Texture
  4. Specific Gravity
  5. Bulk Density
  6. Voids
  7. Porosity and Absorption
  8. Bulking of Sand
  9. Fineness Modulus of Aggregate
  10. Surface Index of Aggregate
  11. Deleterious Materials

1. Composition

Aggregate consisting of such materials that can chemically react with alkalis in cement and cause excessive expansion, cracking, and deterioration of concrete mix should never be used.

Therefore it is necessary to test aggregates to ensure whether there is the presence of any such constituents in aggregate or not.


2. Size and Shape

The size and shape of the aggregate particles greatly influence the quantity of cement required in concrete mix and hence ultimately the economy of concrete.

IS:456 suggests the following recommendations to decide the maximum size of coarse aggregate to be used in PCC and RCC mix.

The maximum size of aggregate particles should be less than, One-fourth of the minimum dimension of the RCC member. One-fifth of the minimum dimension of the RCC member.


3. Surface Texture

The development of hard bond strength between aggregate particles and cement paste depends upon the surface texture, surface roughness, and surface porosity of the coarse aggregate.

If the surface is but porous, maximum bond strength develops. In porous surface aggregates, the bond strength increases due to the setting of cement paste is porous.


4. Specific gravity

The ratio of the weight of oven-dried aggregates maintained for 24 hours at a temperature of 100°C, to the weight of an equal volume of water displaced by saturated dry surface aggregate is termed as the specific gravity of aggregates.

Specific gravity is mainly oh two types:

  • Apparent specific gravity
  • Bulk specific gravity

The specific gravity of major aggregates falls within the range of 2.6 to 2.9.


5. Bulk Density

Bulk density of aggregate may be defined as the weight of the aggregate required to fill a container of unit volume. It is generally expressed in kg/liter.

Bulk density of aggregates particles depends upon the following 3 factors which are:

  • Degree of compaction
  • Grading of aggregates
  • The shape of aggregate particles

6. Voids

The empty spaces between the particles of aggregates are known as voids.

The volume of voids equals the difference between the total volume of the aggregate mass & the volume occupied by the particles alone.


7. Porosity and Absorption

The holes produced in the rocks at the time of the solidification of the molten magma, due to air bubbles, are known as pores.

Water absorption may be defined as the difference between the weight of very dry aggregates and the weight of the saturate aggregates with the surface dry condition.


8. Bulking of Sand

It can be defined as an increase in the bulk volume of the quantity of sand in a moist condition over the volume of the same quantity of dry or completely saturated sand.

The proportion/ratio of the volume of moist sand due to the volume of sand when dry is called a bulking factor.


9. Fineness Modulus

Fineness modulus is commonly utilized to get an idea of how coarse or fine the aggregate is. More fineness modulus value indicates that the aggregate is a coarse sand small value of fineness modulus indicated that the aggregate is finer.

Fineness modulus is a factor obtained by adding the cumulative percentages of aggregate retained on each of the sieves ranging from 80 mm to 150 mm micron and dividing this by 100.


10. Specific Surface Area of Aggregate

The total surface area of aggregate particles per unit weight of the material is called specific surface. This is an indirect measure of the grading of aggregate. The specific surface rises with the reduction in the size of aggregate particles.

The specific surface area of the fine aggregate is very much lesser than that of the coarse aggregate.


11. Deleterious Materials

Aggregate should not contain any harmful material in such a quantity to affect the strength and durability of the concrete.

Deleterious materials might cause one of the following effects on cement or concrete mix:

  • To interfere with hydration of cement
  • To prevent the development of proper bond
  • To reduce strength and durability
  • To modify setting times

Grading of Coarse Aggregate

The coarse aggregate used in making concrete contain aggregates of different sizes. This particle size distribution of the aggregate is termed as “Gradation“. The sieve analysis was conducted to determine this particle size distribution.

What Is Coarse Aggregate | Requirements of Good Coarse Aggregates | Uses of Coarse Aggregates | Classification of the Aggregates
Aggregate Grading

The grading pattern is evaluated by sieving a sample successively through all the sieves mounted one over the other in order of size, with a larger sieve on the top.

The material preserve on each IS sieve after shaking represents the fraction of aggregate coarser than the sieve in and finer than the sieve above. Complete gradation of coarse aggregates is one of the most important factors in producing a workable concrete mix.

Correct gradation makes sure that a sample consists of all standard fractions of aggregate in required proportion such that the sample contains minimum voids. A sample of the well-graded aggregate consisting of lesser voids and will require minimum paste to fill up the voids in the aggregates.


There are three range categories of aggregate grading:

1. Well graded

Well-graded aggregates have a gradation of particle size that fairly evenly spans the size from the finest to the coarsest. A core of well-graded aggregate concrete shoes a packed field of many different particle sizes.

2. Poor Graded

This aggregate is characterized by a small variation in size. It includes aggregate particles that are near the same size. This means that the particles of the aggregate pack together, leaving relatively large voids in the concrete.

3. Gap Graded

Gap graded aggregate consists of aggregate particles in which some intermediate-size particles are missing. A core of gap-graded concrete shows a field of small-seized aggregate interspersed with slightly large aggregate pieces embedded in a small-sized aggregate.

Read More: Fineness Modulus of Sand | Sieve Analysis of Fine Aggregate | F. M. Values


Types of Test Carried Out On The Coarse Aggregates

1. Crushing Value Test of Aggregate (IS 2386 Part IV -1963)

The crushing value is the relative measure of the resistance which can be offered by the aggregate to the crushing under the action of the gradually applied load.

2. Impact Value Test of Aggregate (IS 2386 Part IV -1963)

What Is Coarse Aggregate | Requirements of Good Coarse Aggregates | Uses of Coarse Aggregates | Classification of the Aggregates
Impact Value Test

Impact value Test is carried out on the coarse aggregate to know a relative measure of the resistance offered by the aggregate under the action of suddenly applied load, also known as impact load.

3. Abrasion Value Test (IS 2386 Part IV -1963)

The resistance offered by the aggregate with respect to the wearing is the Abrasion value of the coarse aggregate. It states whether the aggregates are suitable to use for wearing surfaces.

4. Flakiness Index of Coarse Aggregates (IS 2386 Part I -1963)

The flakiness index of the aggregate can be defined as the percentage by the weight of the particles whose minimum dimension or the thickness is less than the value 3/5th of their mean dimension. One can know the thickness of aggregate using the Flakiness Index.

5. Elongation Index of Coarse Aggregate ( IS 2386 Part I -1963)

The elongation index can be stated as the percentage with respect to the weight of the particles whose greatest dimension or length is greater than 1.8 times that of mean dimensions.


FAQs

What is Grading of Coarse Aggregate?

The coarse aggregate used in making concrete contain aggregates of different sizes, this particle size distribution of the aggregate is termed as “Gradation of Coarse Aggregate“. The sieve analysis was conducted to determine this particle size distribution.

What is Coarse Aggregate?

Aggregates which are irregular in shape, broken stones, or naturally occurring round gravels that are used to make concrete, coarse aggregates for structural concrete contain broken stones of hard rock like granite & limestone or river gravels are called Coarse Aggregate

What is the size of Coarse Aggregate?

Particulates of Coarse Aggregate have a size greater than 4.75m. The usual size of coarse aggregate ranges between 9.5mm and 37.5mm in dia.

What is coarse aggregate in construction?

Coarse aggregates are irregular in shape, broken stone or rounded gravel which occurs naturally used as a component for making concrete in construction.

What is Classification Criteria of Coarse Aggregates?

Classification of Coarse Aggregates is done on the following basis,
1.  Classification Of Aggregates Based On Shape
2. Classification of Aggregates Based on Grain Size
3. Classification of aggregates based on Density
4. Classification Of Aggregates Based On Geographical Origin

Coarse Aggregate

Coarse aggregates are irregular in shape, broken stones, or naturally occurring round gravels that are used to make concrete. Coarse aggregates for structural concrete contain broken stones of hard rock like granite & limestone or river gravels.

Coarse Aggregate Meaning

Coarse aggregates are irregular in shape, broken stones, or naturally occurring round gravels that are used to make concrete. Aggregate which has a size bigger than 4.75 mm or which retrained on 4.75 mm IS Sieve are known as Coarse aggregate.

Properties of Coarse Aggregate

Coarse aggregates properties are as follows,
Composition
Size and Shape
Surface Texture
Specific Gravity
Bulk Density
Voids
Porosity and Absorption
Bulking of Sand
Fineness Modulus of Aggregate
Surface Index of Aggregate
Deleterious Materials

Coarse Aggregate Size

The size of coarse aggregate is bigger than 4.75 mm and the fine aggregate has a particle size smaller than 4.75 mm. The most commonly used coarse aggregate size for making concrete is 20 mm.

Define Aggregate

Aggregate which has a size bigger than 4.75 mm or which retrained on 4.75 mm IS Sieve are known as Coarse aggregate.

Coarse Aggregate Size for Concrete

The size of coarse aggregate ranges between 4.75 mm to 80 mm. The most commonly used coarse aggregate size for concrete is 20 mm.

Size of Aggregate Used In Road Construction

The most commonly used coarse aggregate size in road construction is 40 mm, 50mm, 60 mm or as per design requirement. For various layers of road different sizes of aggregates are used.


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3 thoughts on “What Is Coarse Aggregate | Properties of Coarse Aggregate | Uses of Aggregates | Classification of the Aggregates | Aggregates Meaning”

  1. Your last question was what is minimum grade of concrete use I think Thik is incomplete because minimum grade as per your question will be 10 mm because this is lowest grade apart from three option if you mentioned that what is lowest grade concrete for r. C. C. Work than the answer will be 20mm

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