**What is bulk density and % voids of coarse aggregates,****what is bulk density of coarse aggregate of size 20mm** ,in this article discuss about what is bulk density and % voids of coarse aggregates and their nature. As we know bulk density is also called as apparent density or volumetric density which is a not intrinsic property of any material and it can be changed depending on how the material is handled.

Bulk density is defined as ratio of mass of coarse aggregates by the total volume they occupy. Total volume means volume of coarse aggregate, volume of inter particles between them and volume of internal pores present in coarse particles.

In this article discuss about finding the bulk density and voids of coarse aggregate and their Test procedure and also know about what is loose bulk density what is Rooded bulk density ,what is loose coarse aggregate what is compacted coarse aggregate.

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**What is bulk density and their types**

Bulk density is also known as Apparent density or volumetric density and it is property of powder and fine granules and other divided material like minerals, chemical substance, ingredients and food stuffs. It is defined as mass of coarse particles of aggregate divided by the total volume they occupy.

Total volume of coarse aggregate is consist of sum of volume of particles ,volume of inter- particles and volume of internal pores between particles.

Bulk density is not an intrinsic property of any material and it can change depending on how the material should be handled. For example if we poured coarse aggregate into cylindrical metal measure unit will have loose bulk density and when it is disturbed with Tamping rod the coarse aggregate will go and settle closer together resulting in higher bulk density.

**Types of bulk density of coarse aggregate**

Bulk density of coarse aggregate is categorised into two categories depending on how they can poured and settle into cylindrical metal measure unit.

1) **Loose bulk density**

**2) Rooded bulk density**

1) **Loose bulk density** :- it is the ratio of mass of loosely packed coarse aggregate without using tamping rod ,Tamping or rooded to the total volume they occupy

2) **Rooded bulk density** :- it is the ratio of mass of compacted packed of coarse aggregate with the help of Tamping rod or rooded to the total volume they occupy.

**Types of coarse aggregate according to packing**

There are two types of coarse aggregate according to mass and packing

1) **Loosely coarse aggregate**

2) **Compacted coarse aggregate**

1) **Loosely coarse aggregate** :- mass of coarse aggregates which are poured into cylindrical measure unit without any disturbing with tamping rod or setteling.

2) **Compacted coarse aggregate** :- mass of coarse aggregates which are poured into cylindrical measure unit after disturbing with strokes given by tamping rod and setteling after Tamping.

**What is the importance of finding bulk density of coarse aggregate and percentage of voids**

Bulk density of coarse aggregate and their specific gravity along with bulk density of cement fine aggregate and coarse aggregate and specific gravity of coarse aggregate and cement is quite helpful in finding in design of mix concrete like M20,M25,M30 and so on- . When we make design of building structure column beam slab it has requirement of casting of RCC.

casting of RCC work mix concrete should be prepared at the construction site according to design of concrete mix which type of material should be provided, and prepared concrete mix should be tested at the construction site.

**Voids** :- the space between the fine particles of aggregate which was not occupied by solid material that is known as voids.

● **cylindrical metal measure** :- cylindrical measure made of metal product for testing of loose bulk density and rooded bulk density of coarse aggregate and fine aggregate in cylindrical shape. It has three types of cylindrical metal measure

1)** 3 Litre capacity** :- this type of cylindrical metal measure have capacity of 3 litre and of 4.75 mm and less size of fine particles of aggregate are tested to finding it’s loose bulk density and rooded bulk density and percentage of voids

2) **15 Litre capacity** :- this type of cylindrical metal measure have capacity of 15 litre and of 4.75 mm and more upto 40 mm size of coarse particles of aggregate are tested to finding it’s loose bulk density and rooded bulk density and percentage of voids

3) **30 Litre capacity** :- this type of cylindrical metal measure have capacity of 15 litre and of 40 mm size and more above size of coarse particles of aggregate are tested to finding it’s loose bulk density and rooded bulk density and percentage of voids.

4) **Tamping rod** :- tamping rod is 16mm rounded bar of length 600 mm which have tamping nose at one end and second end is rounded and used applying strokes in different layer of coarse aggregate.

**Test procedure for finding loose bulk density**

Test procedure for finding loose bulk density procedure are following

1) **Apparatus required for the test**

**a) weighing balance**

**b) Tamping rod**

**c) straight edge**

**d) Coarse aggregate size of 20 mm sample**

**e) cylindrical metal measure of 15 Litre capacity**

f) observation sheet

2) first we take clean empty cylindrical metal measure unit capacity of 15 litre and weighted it on the weighing balance.take and note their weight in observation sheet.

**W1 = weight of empty cylindrical metal measure unit = 12.5 kg**

3) than we poured loosely packed coarse aggregate of size 20 mm into empty metal measure having capacity of 15 Litres with the help of scoop and aggregate will be poured into vessel least height of 5 centimetre to the top and extra care is being taken that there is no segregation of aggregate particles during the pouring process, now vessel fulfilled with aggregate, and care is being taken that extra amount of aggregate is removed by using straight edge and levelling the top surface of vessel filled with aggregate without disturbing it to setteling. Now weighted the cylindrical metal measure which was filled with aggregate with the help of weighing balance and take their reading

**W2= weight of cylindrical metal measure filled with loosely coarse aggregate of size 20 mm = 32.56 kg**

4) now calculating the net loose weight of coarse aggregate of size 20 mm by subtracting weight of empty cylindrical metal measure from the the weight of cylindrical metal measure filled with loosely coarse aggregate

**Net loose wt = 32.56 _ 12.5 kg**

**Net loose weight = 20.06 kg**

**Volume of aggregate = 15 Litre**

**Loose bulk density = Net loose wt/Volume**

**Loose bulk density = 20.06 kg/15 L**

**Loose bulk density = 1.337 Kg/L**

**Test procedure for finding Rooded bulk density**

1) first we take clean empty cylindrical measurement unit capacity of 15 litre and weighted it on the weighing balance.take and note their weight in observation sheet.

**W1 = weight of empty cylindrical metal measure = 12.5 kg**

2) than we poured loosely packed coarse aggregate of size 20 mm into empty metal measure having capacity of 15 Litres with the help of scoop in three layer first we filled 1/3rd part of vessel and 25 stroke is applying evenly distributed with the help of tamping rod and after that 2/3rd part is filled with pouring aggregate and again we apply 25 strokes with tamping rod and last layres will be poured into vessel least height of 5 centimetre to the top,now vessel fulfilled with aggregate and again applying 25 strokes with tamping rod their top surface is levelling equal to height of cylindrical metal measure with the help of straight edge.

Now take the weight of cylindrical metal measure filled with compacted coarse aggregate with the help of weighing balance and take their reading

**W2 = weight of cylindrical metal measurement filled with compacted coarse aggregate = 36.43 kg**

3) now calculating the net compacted weight of aggregate by subtracting weight of empty cylindrical metal measure from the weight of cylindrical metal measure filled with compacted coarse aggregate

**Net compacted wt = 36.43 _ 12.5 kg**

**Net compacted weight = 23.93 kg**

**Volume of aggregate = 15 Litre**

**Rooded bulk density = Net compacted wt/Volume**

**Rooded bulk density = 23.93 kg/15 L**

**Rooded bulk density = 1.595 Kg/L**

**% of voids present in coarse aggregates**

**Voids** :- the space between the coarse particles of aggregate which was not occupied by solid material that is known as voids. And percentage of voids present in coarse aggregate is calculated with the help of specific gravity of coarse aggregate and their Loose bulk density by the following formula

**% of voids = {(Gs _R)/Gs}×100**

Where Gs = specific gravity of coarse aggregate and their value is 2.65

R = loose bulk density of coarse aggregate = 1.337 kg/L

Putting all this values in formula we get

% of voids = {(2.65 _ 1.337)/2.65}×100

% of voids = (1.313/2.65)×100

% of voids = 0.495×100

Hence % of voids of fine aggregate = 49.5%

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