Home Education Aggregates: 9 Things I Wish You Should Read About It

Aggregates: 9 Things I Wish You Should Read About It

Generally, everyone knows what aggregates are and where it is used but in this blog, there are some important things I wish you should read about it.

It is an inert material which is when bond thoroughly together with cement to form mortar or concrete is called aggregates.

This material has a great influence on man properties of concrete as it occupies more than 75%. It plays a vital role in the properties of concrete such as workability, strength, durability, and economy. So to get the desired size they are processed. The bigger size is coarse aggregate and the small size is fine aggregate.

Air cooled slag of blast furnace and broken bricks are also aggregates.

aggregates used for rigid pavements

Utilization of aggregates

  • Generally, fine aggregates are used to prepare cement mortar, lime mortar, and cement concrete.
  • Coarse aggregates are used to prepare cement concrete (PCC, RCC) bituminous pavement, rigid pavement, etc.
  • Fine aggregate is used in masonry, plaster, flooring, etc. work in building construction.
  • Also, fine aggregate and coarse aggregate are used in the construction of beams columns, slab, lintel, etc. structural members of the building.
aggregates in concrete slabs

Check the below dominant points for more:

  1. What Is An Aggregate?
  2. Requirements of Aggregates
  3. Types of Aggregates.
  4. Properties
  5. Classification Based On Size
  6. Strength of Aggregates
  7. Various Test of Aggregates
  8. Importance
  9. FAQ

What Is An Aggregate?

Aggregates are the naturally occurring material like sand (fine aggregates), crushed rock (coarse aggregates), and gravel. Also, they are processed to get the desired sizes. Broken bricks (brickbats) and crushed air-cooled blast furnace slag are also used as aggregates. The bigger sizes are called coarse aggregates.

Requirements of Aggregates

Requirements of stones

Types of Aggregates

Aggregate may be classified into-

Fine aggregate: When the size of aggregate is 4.75 mm or less (from 150 mm to 4.75 mm) is termed as fine aggregate.
Coarse aggregate: So the aggregates of size between 80 mm to 4.75 mm are known as coarse aggregate.

Properties

  • It should be insoluble in water.
  • They have resistance to corrosion and decay.
  • They are of moderate weight.
  • Also this material has resistance to rainwater and dampness.
  • The weather actions will not be affected.
  • They are strong and durable.
  • They have resistance to scratches.

Classification Based on Size

Fine Aggregate (F.A.)  Coarse Aggregate (C.A.)  
Size ≤4.75 mm
Bulking is more (up to 40%)FA.
Fills voids between C.A.
E.g. natural sand, crushed stone, crushed gravel      
Size> 4.75 mm
Bulking is very small and neglected.
C.A. gives strength to concrete
E.g. Gravel, crushed stone.  

Fine Aggregate (F.A.)

The grading size of material which less than or equal to is termed as fine aggregate.
Generally, the sand considered to have the lowest size of about 0.07 mm. So material which has a size between 0.06 mm and 0.002 mm is termed as silt.

When particles are smaller than 0.002 mm are termed as clay. So loam is a soft deposit consisting of Sand, silt, and clay in between 0.06 mm are termed equal proportions.

So the finer are divide into four grading zones according to IS 383-1970
In short, the zone of grading will become finer from coarser as we progress in grading from Zone I to zone IV.

aggregates used in railway tracks

Coarse Aggregate (C.A.)

The aggregate which has a size bigger than 4.75 mm is termed as coarse aggregates.
So the various nominal sizes will describe the grading of coarser which are 12.5mm, 16mm, 20mm, 40mm, etc. For example, a graded aggregate of nominal size 12.5 mm means an aggregate most of which passes the 12.5 mm I.S. sieve.

So the maximum size of this material one can be used for making concrete is 80 mm.

In addition utilizing the possible biggest size which leads the result in,
(i) Cement content reduction.
(ii) Water requirement reduction
(iii) Drying shrinkage will be reduced.

The following conditions play a vital role in deciding the maximum size of aggregate that one can use during construction.

(i) Section thickness
(ii) Reinforcement spacing
(iii) Clear cover
(iv) Mixing, handling, and placing techniques.

Maximum Size of Aggregate

Generally, for strengthened concrete work, the material has a max size of 20 mm is usually considered fine for the member as specified in IS: 456-2000.

So for RCC work the nominal maximum size should usually be limited to 5 mm less than the minimum clear distance between main bars or 5 mm less than the minimum cover to reinforcement, whichever is smaller.

So for reinforced concrete work, aggregates having a maximum size of 20mm size for RCC work are marked as satisfactory.

Plum Concrete

Rubbles which are 160mm or greater than it used in simple concrete then this type of concrete is plum concrete.

The amount of rubble as much as the most restriction of 20 in keeping with percent by way of the extent of the concrete is used when specially authorized.

Firstly the rubbles are located on approximately 60 cm thick plastic concrete at some distance apart afterward the plastic concrete is vibrated by the means of internal vibrators. Later then the rubbles sink into the concrete.

This technique of incorporating big boulders within the concrete is also known as displacement concrete.

In Maharashtra at Koyna Dam this method has utilized for construction.

All-in-Aggregate

Eventually, sometimes combined aggregates comprising different fractions of finer and coarser are available in nature. Hence they known as all-in-aggregate. Like coarser the all in one aggregate is also described by its nominal size.

Generally, all-in-one aggregates are not used for making high-quality concrete.

Table-Grading Limits of All-in-aggregates (IS: 1970)

IS sieve DesignationPercentage by weights passingPercentage by weights passing
40 mm nominal size20 mm nominal size
80 mm100
40 mm95-10095-100
20 mm45-7530-50
4.75 mm25-4510-35
600 micron8-300-6
150micron0-60-6

Single Size Aggregate

When they comprising the majority of particles that are of nearly the same size are called Single size . For example, a 20 mm single size aggregate means an aggregate most of which passes through a 20 mm s sieve size and the major portion of which is retained on a 10 mm IS sieve.

Strength of Aggregates

So the compressive strength of concrete depends upon the quality of cement paste and the bond between the cement paste and the aggregate.

So if the strength and many other energy of the paste or the bond among the paste and aggregate is low, a concrete of bad quality is received irrespective of the power of the aggregates. 

However when cement paste of good or excellent quality is provided and its bond with the mixture is first-class, then the mechanical residence of the mixture will impact the strength of concrete.

As strong aggregates cannot make strong concrete, but for making strong concrete, strong aggregates are an essential requirement.

Various Tests For Aggregates

Generally following tests are prescribed for the determination of strength of aggregate namely

  1. Aggregate crushing value test
  2. Aggregate Impact value test
  3. Ten percent fines value test
  4. Aggregate abrasion value test.
Aggregates Impact value Test

Importance

The broken stones of Ballast rock are used as coarse aggregate in building construction and also in road construction work. Also they make the volume of work.

So in cement Concrete proportion of coarse aggregate is quite high compare to cement and sand. Meanwhile binder material works well with the use of this aggregate. Also Coarse aggregate is used in R.C.C. structures of the building. Also they provide strength and stability to the building.

FAQ

1) Which aggregates have high shrinkage?

According to the study it is found that aggregates made from sandstone have a high amount of shrinkage issues.

2) What aggregates are used in concrete?

Generally, 20 mm size which is coarser been used.

3) How are aggregates graded?

Generally, a sieve test has been used to determine the particle size distribution of it.

4) Can aggregates be recycled?

Yes, it’s been recycled through a process and reused once again for construction or for other purposes.

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