Aggregates are used in concrete to provide economy in the cost of concrete. Aggregates only act as fillers. These do not react with cement and water.

But there are properties or characteristics of the aggregate that affect the properties of the resulting solid mixture. These are as follows.

  1. Combination
  2. size shape
  3. surface texture
  4. specific gravity
  5. bulk density
  6. Vacancies
  7. porosity and absorption
  8. sand. bulk of
  9. fineness modulus of aggregate
  10. Surface Index of Aggregates
  11. harmful material
  12. crushing value of aggregate
  13. impact value of aggregate
  14. frictional value of aggregate

1. Combination

Aggregates containing materials that can react with alkalis in cement and cause excessive expansion, cracking and spoiling of the concrete mix should never be used. Therefore it is necessary to test the aggregate to know whether there is a total presence of any such component or not.

2. size shape

The size and shape of aggregate particles greatly affects the amount of cement required in the concrete mix and hence ultimately affects the economy of the concrete. For the preparation of economical concrete mix, the largest coarse aggregate practicable for the structure should be used. IS-456 suggests the following recommendations for determining the maximum size of coarse aggregates to be used in PCC and RCC mixes.

The maximum size of the set must be less than

  • One fourth of the minimum dimension of the solid member.
  • One fifth of the minimum dimension of the reinforced concrete member.
  • Minimum clear gap between reinforced bars or 5 mm less than minimum cover between reinforced bars and form, whichever is smaller for heavy reinforced concrete members such as ribs of main bars.

Remember that the size and shape of the aggregate particles affect the properties of freshly mixed concrete more than hardened concrete.

Read also: How to classify aggregates on the basis of size

Read also: How to classify aggregates on the basis of size

3. surface texture

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

If the surface is rough but porous, maximum bond strength is developed. In porous surface aggregates, the bond strength is increased due to the setting of cement paste in the pores.

4. specific gravity

The ratio of weight to oven dried aggregates for 24 hours is 100 to 110 . is maintained at a temperature of0c, is known as the specific gravity of the aggregate for a weight of the same amount of water displaced by the saturated dry surface aggregate.

There are mainly two types of specific gravity.

  • apparent specific gravity
  • bulk specific gravity

Specific gravity is a means of determining the suitability of an aggregate. Low specific gravity usually indicates porous, weak and absorbent material, while high specific gravity indicates material of good quality. The specific gravity of the major aggregates falls within the range of 2.6 to 2.9.

Specific gravity values ​​are also used when designing a concrete mix.

Read also: Specific gravity and water absorption test of aggregates

5. bulk density

It is defined as the total weight required to fill a container of unit volume. It is usually expressed in kg/litre.

The bulk density of an aggregate depends on the following 3 factors.

  • degree of compaction
  • grading of aggregates
  • total particle size

6. Vacancies

The spaces between the aggregate particles are called spaces. The volume of zero is equal to the difference between the gross volume of the total mass and the volume occupied by the particles alone.

Read also: Zero test of bulk density and aggregate

7. porosity and absorption

The tiny holes formed in rocks during the solidification of molten magma due to air bubbles are called pores. Porous rocks are called porous rocks.

Water absorption can be defined as the difference between the weight of very dry aggregate and the weight of saturated aggregate with dry surface conditions.

Depending on the moisture content in the aggregate, it can be present in any of 4 conditions.

  • Very dry aggregates (no moisture)
  • dry aggregate (there is some moisture in its pores)
  • Saturated surface dry aggregate (pores are completely filled with moisture but there is no moisture on the surface)
  • Moist or wet aggregates (pores are filled with moisture and there is also moisture on the surface)

8. sand. bulk of

It can be defined as an increase in the bulk amount of sand (i.e. fine aggregate) in moist condition over the same amount of dry or fully saturated sand. The ratio of the volume of moist sand to the volume of sand when dry is called the bulking factor.

Fine sand has more bulk than coarse sand

When water is added to dry and loose sand, a thin layer of water forms around the sand particles. The interlocking of air between the sand particles and the water film causes the surface tension to separate the particles and thereby increase the volume. But in case of fully saturated sand the water film breaks down and the volume becomes equal to that of dry sand.

Also read: Pile of sand – what, why and how?

9. fineness modulus

The fineness modulus is an empirical factor obtained by adding the cumulative percentage of the aggregate formed on each standard sieve of 80 mm to 150 µm and dividing this amount by 100.

The fineness modulus is commonly used to estimate how thick or fine an aggregate is. A higher fineness modulus value indicates that the aggregate is thicker and a smaller fineness modulus value indicates that the aggregate is finer.

Also read: Gross’s Modulus of Beauty – What, Why and How

10. specific surface of aggregate

The surface area per unit weight of the material is called specific surface. It is an indirect measure of overall grading. The specific surface increases with a decrease in the total particle size. The specific surface area of ​​fine aggregate is much higher than that of coarse aggregate.

Also read: How To Calculate The Total Surface Index Of An Aggregate

1 1 harmful material

The aggregate should not contain any harmful material in such quantities as to affect the strength and durability of the concrete. Such harmful substances are called harmful substances. Harmful ingredients may cause one of the following effects

  • To interfere with the hydration of cement
  • to prevent the development of the proper ligament
  • to reduce strength and durability
  • To modify the setting time

Harmful materials generally found in aggregates can be classified as

  • organic impurities
  • soil, silt and dust
  • salt contamination

Read also: Determination of light weight pieces in aggregates

12. crushed value

The aggregate crushing value gives a relative measure of the resistance of an aggregate to crushing under a gradually applied compressive load. Aggregate crushing strength value is a useful factor to know the behavior of aggregate when subjected to compressive load.

Also read: Crushing Value Test of Aggregates

13. impact value

The total impact value gives a relative measure of the total’s resistance to a sudden shock or impact. The impact value of an aggregate is sometimes used as a substitute for its crushing value.

Read also: Impact value test of aggregates

14. frictional value of the aggregate

The friction value gives a relative measure of the wear resistance of an aggregate when it is rotated in a cylinder with some abrasive charge.

Read also: Friction value test of aggregates

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.