Bulking of sand – (Factor affecting, Significance, and Prevention)

 What is Bulking of sand?

When sand comes in contact with water, its volume increases due to the presence of moisture. This phenomenon of sand is called the bulking of sand.

When sand gets contact with water, a thin film of water is formed around the sand particle that makes them get apart from each other due to the pushing force of surface tension resulting in the increase in the volume of sand.

It is studied that, only 4% of moisture can increase the sand volume up to 15-30%, but depends upon grading.

The finer sand result in extreme bulking than that of medium and coarse sand. If the water is added than its maximum capacity, the film around particles gets a break that makes sand particles come closer and result in a decrease in volume i.e. no bulking takes place.

Therefore, we get same volume of dry sand and fully saturated sand.

From the graph, we can know that the maximum bulking takes place from 5 – 10% of moisture content and when moisture content increases from 20% volume of moist sand tend to be equal with the volume of dry sand.

Limit of bulking in the sand as per IS2386-3:

Moisture content:	% of bulking:
2%	15%
3%	20%
4%	25%
5%	30%

Test for bulking of sand:

Method 1:

Apparatus required:

1. Sand sample
2. Weighing machine
3. Graduated cylinder
4. Tray
5. Container

Procedure:

Step 1: Take 300g of oven dried sand sample.

Step 2: Measure dry sand volume by filling it in graduated cylinder and note it.

Step 3:  Take a water 1% by weigh of sand. Here we take 3-gram of water.

Step 4: Mix the measured water and sand thoroughly to get the uniform mix.

Step 5:  Now measure the volume of sand (with 3gm water) in the graduated

   cylinder. Note the volume.

 Step 6: Again add 3 gm of water (1% by weight) to the same sample from step 4

                And thoroughly mix them to get uniform mix.

Step 7:  Now measure the volume of sand (with 6 gm of water) and note its

    Volume.

Step 8: Repeat the same process for 3 more times for accurate result.

Observation table:

Added water weight (gm)	Total water added (%)	Height of sand (ml)	Increase in vol. (%)
3	1
3	2
3	3	X	Y
3	4
3	5

Here, volume will increase and reach to maximum at one point and gradually decrease. Let us consider Y be the maximum volume.

And height of oven dried cylinder be= A

Height of sand at its maximum volume= X

Now,

            The % bulking of sand at 3% moisture content = ((X – A) *100) / A

Method 2:

Apparatus required:

1. Measuring cylinder,
2. Moist sand sample.

Procedure:

Step 1: Fill the measuring cylinder with the moist sand for about 4/5 part of the

             Cylinder.

Step 2: Now fill the remaining part of the cylinder with water.

Step 3: Wait until it is completely saturated and then measure the volume.

Let, the initial volume of sand = V₁

Let, volume of sand after complete saturation= V₂

Now,

            % of bulking of sand= ((V₁-V₂) *100)/ V₂

Plotting graph between volume of sand and % water added:

Effect of bulking sand in concrete mix:

Sand is used in the cement in order to fill the gap between cement and coarse aggregate resulting in the reduction of segregation. There will be no effect of the bulking of sand if weight batching is adopted while batching the aggregates.

But when batching by volume is adopted, the sand will be taken less than the requirement in the mix, and this result in disproportionate and non-uniform mix. So, to overcome this the volume of sand is increased by percentage bulking.

Here are some effects of bulking sand on concrete:

1. The yield strength of the concrete is affected by the bulking of concrete.
2. The water in the sand is useful for maintaining the water-cement ratio that helps in improving the workability.
3. An excessive amount of moisture can reduce the strength of concrete.
4. If proper management of bulking of sand for concrete is not done then it may result in under sanded mixes can be harsh and make it difficult for working and placing.

Factor affecting the bulk density:

1. Particle size:

Dry sand of finer size has more air voids around the mineral particles than that of the coarse sand resulting in more bulking. So, bulking of sand is more for finer sand than goes on decreasing for coarse sand.

• Particle shape:

Bulk density also depends on how particles are arranged in the sand as shape distribution govern how particle will be packed together resulting in the increase of bulk density.

• Pores in sand:

It depends upon the pore space present in the soil. The higher porosity of soil results in lower bulk density because bulk density depends upon combined volume of solid and pore space.

• Moisture content:

As the moisture content is increased bulking of sand also goes on increasing. But when it reaches to the maximum point i.e. 4-6 % of moisture content makes 25-40%, after that it goes on decreasing.

Significance of bulking of sand:

1. It is useful for reducing the pores in the sand and compacting the sand resulting in the increase in volume.
2. It helps for maintaining workability and placing of concrete.
3. Helps in reduction of segregation by filling the pores between cement and aggregates.
4. It helps to give concrete a uniform structure.

limitations of bulking of sand:

1. Improper bulking of sand can result in harsher concrete and less workability.
2. Unmanaged bulking of sand can decrease the yield of concrete.
3. It can affect water-cement ratio in concrete.
4. If not meet the standard concrete mix proportion, it will hamper the strength and durability of concrete.

Prevention of bulking of sand:

We should use the bulk sand that contains less sand and water while mixing the concrete. If any deficiency occurred or if water level reaches more than required than we can overcome this problem by adding some more amount of sand.

Moisture containing less than 5% can be considered for construction work.

I hope this article remains helpful for you.

Happy Learning – Civil Concept

Contributed By,

Civil Engineer – Shreya Parajuli

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