Bulking of sand is an important criteria for mix design of concrete. So this is calculated either by laboratory method or field method.
Bulking of sand mainly depends upon percentage of moisture content of sand and size of aggregates (coarse or fine )
This percentage of bulking is included while taking mix proportions otherwise segregation or honeycombing will takes place.
Table of Contents
Phenomenon of bulking of sand
When water or moisture content comes in contact with sand forms a thin layer between the sand particles and exerts pressure between particles results in expansion of sand thus volume also increases.
With increase in moisture content volume of sand also increases and this phenomenon is known as bulking of sand.
Note : with increase in moisture content of sand, Volume also increases up to a certain peak level but at the point of saturation stage both dry and wet volumes of sand are equal.
Then,
What is the use of bulking of sand ?
when you are preparing a concrete mix we have to add cement,coarse aggregates, fine aggregates, water, admixtures to proper binding and filling all the voids. If you mis-proportionate any of these materials results in harsh mix.
Harsh mix causes segregation or honeycombing in concrete.
Let’s suppose
Example : If the bulking of sand is 20% and if you ignore while mixing in 1 m^3 concrete then total volume becomes 80% only after adding water.( 20% deficient in sand )
This results in reducing sand proportions and directly effects on strength of concrete. So it’s important to consider extra 20% of sand or 1.25 while taking mix proportions.
Generally we consider wet volume of concrete is 1.5 times the dry volume, here typically { 30% bulking of sand + 20% wastage }
Now, I think you have understood the importance of bulking , But how to find bulking of sand and To determine maximum increased in volume.
Bulking factor
It is the Ratio of given dry volume or percentage change in dry volume with dry loose sand after molding.
For more detail read this Test procedure
IS code book for finding bulking of sand
IS 2386 (PartIII) 1963 Download
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How do you calculate bulking of sand ?
Bulking is calculated by two methods; laboratory method and field method.
Why we have to learn two methods ?
Because laboratory method is used for weigh batching and field method is used for volume batching.
1. Laboratory Test for bulking of sand :
Apparatus :
- Vessel
- Tamping rod
- Tray
- Fine aggregates and water
Procedure
- Compact the sand in three layers in the vessel, each layer being tamped 25 strokes and strike level at top
- weigh it and dump into a tray
- Add a certain percentage of water 2% by weight of dry compacted sand { 0.02 * W1 }
- Mix well till uniformly moist
- Fill container with the wet sand without any tamping
- Strike top surface levels and find weight of the wet loose sand
- Repeat the same with water contents of 4%, 5%, 6%, 8%,12%,15% … respectively.
Observations and calculations
weight of dry compacted sand = W1 { unit volume }
Weight of loose wet sand = W2 {unit volume }
If moisture content be x% in loose sand and if W3 is weight of dry sand in loose sand (w2)
Then, W2 = W3 + ( X/100 ) W3
therefore W3 = W2 / ( 1+ X% )
From bulk factor equation ; BF = W1 / W3 { weight of dry sand to weight of same sand after molding }
so, Bulking percentage = ( W1 – W3 ) / W3 * 100
Graph:
Draw a graph between percentage of moisture content on x-axis vs percentage of bulking on y-axis.
The points on graph added as a smooth curve. Then from the graph determine maximum percentage of bulking and corresponding moisture content.
Result :
1 . Average bulking percentage = { Do average of all the bulking percentages }
From the graph ;
2 . Max bulking percentage = { Max bulking value from graph and corresponding moisture content }
2. Field Method
Apparatus
- Balance and weights
- Tray
- Spatula
- Measuring cylinder
Procedure
- Take a 250 cc of dry sand and find it’s weight
- Add 2% of water and mix thoroughly to get damp sand
- Pour the damp sand in the 250 cc measuring cylinder up to 200 cc mark
- Fill the cylinder with water until the sand is fully submerged and there is standing water of 2 to 3 cm over it.
- Stir the sand well with poker to remove any air bubbles and note the second level Y cc
- Now Repeat the moisture contents of 4%, 5%, 6%, 8%, 12%, 15% and 20% respectively.
Observations and calculations
now ; Bulking factor (BF) = 200 / Y
Percentage of bulking = (200 – Y) / Y *100
Graph
Draw a graph between percentage moisture content on x-axis vs percentage bulking on y-axis
Points on the graph added as a smooth curve. Then from the graph determine maximum percentage of bulking and corresponding moisture content.
Result
1 . Average bulking percentage = { Do average of all the bulking percentages }
From the graph ;
2 . Max bulking percentage = { Max bulking value from graph and corresponding moisture content }
Conclusion :
From this article we learned about bulking of sand, bulking factor , Also two methods of calculating bulking of sand .
Thank you for staying with us !
Hope your doubts are cleared also share with your friends !
FAQ’s
Q1 ) Is the rate of bulking is same for coarse and fine sand ?
Ans : Rate of Bulking is inversely proportional to size of particles. As the size of particles goes on increasing percentage of bulking decreases and becomes negligible.
So we consider bulking factor only for fine aggregates and this phenomenon is neglected in case of coarse aggregates.
This { figure 2 } shows rate of bulking in the case of fine aggregates is more compared with medium and coarse sand.
Q2 ) What is the Difference between bulking and bulking factor ?
Ans : Change in volume is known as bulking and measure of bulking is known as bulking factor.
Q3 ) Why is the bulking of a coarse aggregate less compared to a fine aggregate?
Ans : The main reason is particle size; As in case of fine aggregates water forms thin layer between particles. But that doesn’t happen in case of Coarse aggregates because particles are large in size so bulking phenomena is neglected.
Q4 ) Is bulking of sand makes money ?
Yes ! Justify this statement below in comment section if you know answer
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