Bulking of sand and its determination on site

What is Bulking of Sand?

According to Mr. M. Chakraborth, bulking of sand is the increase in volume of dry sand due to absorption of moisture which forms a thin film of water around the particles of sand by frictional resistance.

• In other words, there forms a thin layer of water film around the particles of sand, which due to surface tension does not let 2 particles of sand to come in direct contact.

• So, naturally there is space between the sand particles which is filled by the thin water film. This is the cause of bulking of sand.

Why is it important to consider bulking of sand?

• Bulking of sand could be as high as 40% to the volume of sand.

• It is best practice to batch concrete by weight, but this is not always practical in every situation. For normal concrete works, batching is usually done locally and by volume.

• Change in the volume of sand in concrete mix means that, the mixed concrete is mot of the desired quality. Slump value will change affecting compaction and workability.

• Also the strength of the concrete after 28 days will not be of the desired value.

How to calculate Bulking of Sand?

Determination of bulking of sand is a very simple and quick test which can be done at the site. All you will need is a glass jar with uniform surface area from top to bottom.

Step 1:-

Add the sand which needs to be tested to the glass jar almost to the brim, but leave a little space at the top. Do not compact the sand but just level the sand and measure the height (H).

Step 2:-

Now add water to the sand in the glass jar and stir the contents. Note that there should be plenty of water which would saturate the sand. Let the contents in the jar settle and level the sand. Measure the height (h).

Calculation:-

H-h will give you the difference in the volume.

[(H-h)/h]x 100 = percentage of bulking.

Use this value to correct the effect of bulking of sand.

When to do this test?

If you are going to batch by volume, it is always desirable to do this test. But you must conduct this test especially if its rainy season and the climate is moist.

It is important to note that finer sand will bulk more compared to coarser sand. Also this test is not necessary for coarse aggregate as the bulking is very negligible.

The following books were used as references, also I personally used these books while doing my engineering.

References:-

Concrete Technology (Theory and Practice) - by M.S Shetty - S Chand & Company LTD.

Estimating, Costing, Specification and Valuation in Civil Engineering - by M. Chakraborth - 25th edition.