Bulking of sand is an increase in the volume of sand due to an increase in moisture content and a film of water is created around the sand particles which force the particles to get aside from each other.
When the moisture in sand increases then the volume of sand increases and the bulking of sand depends on the quality of moisture in the sand and also the particle size.
The volume of the sand can increase up to 20 to 40 percent due to a 5 to 8 percent increase of moisture in the sand and for coarser sand, the increase in volume will be relatively less.
On the moisture in the sand bulking of sand depends upon it but the particles of sand get packed near each other as the film around the sand particles breaks and the bulking is reduced when the moisture is increased by adding more water.
Before using the sand in the construction, a bulking test on fine aggregates or sand has to be performed.
Causes of Bulking of Sand:
Around sand particles, the moisture content in the sand makes thin films and each particle exerts pressure then increasing in the volume causes because they move away from each other.
There are two factors on which bulking of sand depend;
The fineness of the aggregates &
Percentage of moisture content.
Determination of Bulking of Sand:
There are two tests for a determination as given below;
Laboratory Test for Bulking of Sand.
Field Test for Bulking of Sand.
Laboratory Test for Bulking of Sand:
There are the following apparatus used in the laboratory test for bulking of sand such as;
At a temperature of 100 to 110 degrees Celsius for 24 ± 0.5 hours take 500 grams of fine aggregate and this weight is measured as or equal to W1.
In an airtight container, the cooled sand is taken and measured weight is as W2.
The sample water content is calculated as; Wc = (W1-W2) x 100/W1
250 grams of sand is taken in a pan and 2 percent by weight of water is added and mixed properly.
Into a 250ml cylinder the mixture is poured and by shaking this is consolidated. Then the surface is leveled and as Y1 the reading is measured.
For 2% of water by weight each time, the test is repeated for the remaining quantity of sand and as Y2 & Y3, etc the readings are taken until the decreasing volume readings.
Then the water is added and the test is continued until the sample becomes fully saturated and adds about 50 ml water ore and stir the sample well in the measuring cylinder.
Note down the surface level of inundated sand as Y ml.
Calculations and Results:
Bulking of sand percentage = (Y1-Y) x 100/Y
With the percentage of water content along X-axis and percentage bulking along y-axis a graph is plotted and the following results are obtained from the graph;
Percentage (%) of bulking occurred.
Percentage (%) at maximum bulking of water content.
Percentage (%) of water content when bulking is zero.
Percentage (%) of bulking for the initial water content (W) of the sample.
Field Test for Bulking of Sand:
For bulking of fine aggregates field test determines the necessary adjustment required.
Measuring Cylinder of 250 ml.
Into 250 ml measuring cylinder up to the 200 ml mark pour the sand.
With water fill the cylinder and stir well as to submerge the sand completely sufficient water should be poured and the sand surface is seen to be below its original level.
At the sand surface (Y ml), take the readings.
Bulking of sand percentage, % = [(200/Y)- 1] x100
Importance of Determining Percentage Bulking:
Due to bulking unrealistic volume is shown by fine aggregate and the sand bulking issues are concerns when concrete proportioning is to be performed.
The concrete designed will have an insufficient amount of sand resulting in a harsh mix if the effect of bulking is not studied properly and the bulking of sand will affect the concrete yield for given cement content.