Theory:
Increase in volume of sand due to presence of moisture is known as bulking of sand. Bulking is due to the formation of thin film of water around the sand grains and theinterlocking of air in between the sand grains and the film of water. When more water is added sand particles get submerged and volume again becomes equal to dry volume of sand.
Due to the bulking, fine aggregate shows completely unrealistic volume. Therefore, it isabsolutely necessary that consideration must be given to the effect of bulking in proportioning the concrete by volume. If cognisance is not given to the effect of bulking, in case of volume batching, the resulting concrete is likely to be under-sanded and harsh. It will also affect the yield of concrete for given cement content.
To compensate the bulking effect extra sand is added in the concrete so that the ratio of coarse to fine aggregates will not change from the specified value.
Maximum increase in volume may be 20 % to 40 % when moisture content is 5 % to 10 % by weight. Fine sands show greater percentage of bulking than coarse sands with equal percentage of moisture.
Objective:
To ascertain the bulking phenomena of given sample of sand.
Reference:
IS: 2386 (Part-3)-1963.
Apparatus:
Beaker, 1000ml measuring jar, brush, scale, mixing tray.
Material:
Fine aggregate, water.
Procedure:
1. Put sufficient quantity of dry sand into the beaker until it is about one-thirds full.
2. Level off the top of the sand and measure the height (H1) by pushing a steel rule vertically down through the sand at the middle to the bottom. Measure weight of the sand.
3. Add 2% of water; mix it thoroughly in the container. Smooth and level the top
surface measure the height (H2) of soil. Find the height percentage increment.
4. Repeat the same procedure with increasing amount of water by 2% until
percentage increment of sand height is reduced and attends original level.
5. Plot a graph of percentage increment of sand height against percentage of water.
(Note: A typical bulking of sand graph looks like Figure 5)
Results and discussions:
From the tabulated results and the plotted graph is is observed that, the given sand specimen under goes maximum bulking at _________% of moisture contain. Maximum percentage of bulking is __________.
Precautions: (Discuss about the precautions to be taken while conducting this experiment)
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Questions:
1. What is meant by bulking of sand? Why it happens?
2. What is the significance of bulking of sand experiment?
3. Define bulking factor?
4. What is the effect of moisture on bulking?
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