What is Bulking of Sand? Causes and Test Formula

Bulking of sand becomes a big problem in construction and engineering applications because the volume of sand changes significantly from dry to wet which potentially lead to instability and failure.

Bulking of Sand: Test As Per IS:2386 Part-3 Causes, Formula

Bulking of sand is a phenomenon in which the volume of sand increases due to the presence of water which is caused by the formation of a thin layer of water around each sand particle which reduces the friction between the particles and allows them to move more freely. As its result, the sand particles can pack more loosely to increasing the overall volume of the sand.

Bulking of Sand: Test As Per IS:2386 Part-3 Causes, Formula

The amount of bulking of sand depends on the moisture content and particle size of the sand. It is seen that the higher the moisture content of sand having the greater the bulking of sand. Since, finer sands have more surface area per unit volume, therefore they show a greater degree of bulking than coarser sands.
To mitigate the effects of bulking of sand, engineers may use techniques such as compaction or drying the sand before use. Also, they can calculate bulking of sand to adjust the quantity accordingly.

What is Bulking of Sand?

Bulking of sand refers to the phenomenon where dry sand experiences a significant increase in volume when it comes into contact with moisture or water. This expansion occurs due to a thin film of water forming around individual sand particles, causing them to repel each other rather than pack closely together.
Consequently, the sand particles occupy more space than they would in their dry state, leading to an apparent increase in volume. Bulking can have substantial implications in construction and engineering, impacting the accuracy of measurements, the workability of concrete mixes, and the overall quality and durability of construction projects.
As such, understanding and managing the effects of sand bulking are essential for ensuring the successful completion of various construction endeavors.

Bulking of Sand Formula

The bulking of sand refers to an increase in its volume when it is saturated with water. The formula for calculating the bulking of sand as per the Indian Standard IS:2386 Part-3 is as follows:

Bulking of Sand (%) = [(Vol of saturated sand - Vol of dry sand) / Vol of dry sand] × 100
In this formula:
  • Volume of saturated sand is the volume occupied by the sand when it is completely saturated with water. This is typically measured by filling a container (usually a cylindrical container) with dry sand and then gradually adding water until it reaches a constant level.
  • Volume of dry sand is the initial volume of the same dry sand before it is saturated with water.
The bulking factor is usually expressed as a percentage, and it represents how much the volume of sand increases when it transitions from a dry state to a saturated state. This information is important in construction and engineering applications, particularly when estimating the quantity of sand needed for concrete or mortar mixes, where the volume of sand in its wet (saturated) state is different from its dry state. See the test procedure below in detail.

How to Overcome From Bulking of Sand?

To overcome the problem of bulking of sand, it is necessary to determine the degree of bulking of sand for a particular type of sand and adjust its quantity used accordingly. This can be achieved by conducting a simple test to determine the bulk density of sand with different moisture contents. 
Based on the test results, an adjustment factor can be determined and used to compensate for the bulking effect. Otherwise, we can use dry sand if possible to minimize the effect of bulking of sand.

Methods To Determination of Bulking of Sand As Per IS:2386 Part-3

The bulking of sand can be determined by conducting a simple field test known as the bulking test of sand (fine aggregate). The test involves measuring the volume of a known weight of dry sand and then measuring the volume of the same weight of sand after it has been saturated with water.
The procedure to be adopted may be varied, but there are two methods which are suggested and both methods depend on the fact that the volume of inundated sand is the same as if the sand were dry. 

1. Determine Bulking of Sand As Per IS:2386 Part-3 (Field Method)

Follow the steps below to determine bulking of sand:

Step-1: Put sufficient quantity of the sand loosely into a container until it is about two-thirds full. Level off the top of the sand and pushing a steel rule vertically down through the sand at the middle to the bottom, measure the height as h cm.

Step-2: Empty the sand out of the container into another container where none of it will be lost. Fill half of the first container with water. Put back about half the sand and rod it with a steel rod about 6 mm in diameter, so that its volume is reduced to a minimum. Then add the remainder of the sand and rod it in the same way.

Step-3: Smooth and level the top surface of the inundated sand and measure its depth at the middle with the steel rule and measure this is h’ cm.

Step-4: The percentage of bulking of the sand due to moisture shall be calculated from the formula:

Bulking of Sand (%)= [(h/h') -1]×100


2. Determine Bulking of Sand As Per IS:2386 Part-3 (Field Method)

Follow the steps below to determine bulking of sand:

Take a 250 ml measuring cylinder and pour the damp sand (consolidated by shaking) until it reaches the 200 ml mark.

Step-2: Then fill the cylinder with water and stir the sand well (the water shall be sufficient to submerge the sand completely). It is seen that the sand surface is now below its original level. Measure volume at the surface height as y ml.

The percentage of bulking of the sand due to moisture shall be calculated from the formula:

Bulking of Sand (%)= [(200/y) -1]×100

Test Result

Report the percentage bulking of the sand to the nearest whole number.

Lab Report: Moisture Content of Sand Vs Bulking of Sand By Volume

The test result of bulking of sand is reported as the nearest whole number. See the approximate value of bulking of sand with its moisture content.

Bulking of Sand: Test As Per IS:2386 Part-3 Causes, Formula

Note: The above values of bulking of sand are approximate and can vary based on the specific type and properties of the sand being used as well as other factors such as compaction and particle shape.

What are the Causes of Bulking of Sand?

Bulking of sand, also known as swell or expansion of sand, occurs when sand particles increase in volume due to the presence of moisture. Several factors can contribute to the bulking of sand:

1. Moisture Content

The primary cause of sand bulking is an increase in moisture content. As sand absorbs water, a thin film of water molecules coats the surface of individual sand particles. This coating causes the particles to repel each other, resulting in an expansion in volume.

2. Particle Shape

The shape of sand particles plays a role in bulking. Angular or irregularly shaped particles tend to experience more significant bulking compared to well-rounded particles. Angular particles have more surface area and can trap water between them, causing greater expansion.

3. Particle Size Distribution (Gradation)

The gradation or particle size distribution of sand can also influence bulking. Finer sands, such as those with smaller particle sizes, tend to exhibit more pronounced bulking because they have a higher surface area to volume ratio and can retain more moisture.

4. Clay and Silt Content

Sands that contain clay or silt particles can experience increased bulking due to the water-absorbent nature of clay and silt. These fine particles can absorb and hold water, causing the sand to swell.

5. Organic Matter

The presence of organic matter in sand can act as a sponge, holding water and contributing to bulking. Organic matter, such as decomposed plant material, can increase the moisture retention capacity of the sand.

6. Compaction

The degree of compaction can influence the extent of bulking. Loose, uncompacted sand tends to exhibit more significant bulking than densely compacted sand because there is more space between particles for water to occupy.

7. Salt Content

High salt content in sand can lead to a phenomenon known as "salt bulking." Salt attracts moisture and can cause sand to swell more than usual.

8. Temperature

Temperature variations can affect the moisture content and bulking of sand. For example, freezing and thawing cycles can lead to the expansion and contraction of moisture within the sand, causing bulking in colder climates.

What are the Effects of Bulking of Sand?

Understanding the effects of bulking of sand is important in ensuring safe and successful construction and engineering projects. Proper management and mitigation strategies can help minimize the negative impacts of bulking and ensure that the sand is used effectively and efficiently. The effects of bulking of sand can be significant in various applications. Some of the main effects are given below:

1. Defects in Measurement

When sand bulks due to the presence of water, its volume increases. This can be a problem in construction projects where precise measurements and volume calculations are essential. It can also lead to instability and failure of structures if the sand shifts or settles.

2. Strength Reduction of Structure

Bulking of sand can reduce the strength of the sand, making it less stable and more prone to movement. This can be a problem in applications such as foundation construction, where stable and strong materials are crucial.

3. Workability Issues Generated Due to Bulking of Sand

Bulking can make the sand more difficult to work with. As sand becomes more fluid and less stable due to bulking. This can affect the ability to form and shape the sand for various applications.

4. Transport and Storage Problems

Bulking of sand can make it more difficult to transport and store sand. As the increased volume of sand can lead to space and weight issues. This can be a problem in industries such as mining and construction where large quantities of sand are often used.

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