The volume increase of fine aggregate due to presence of moisture content is known as bulking. Fine sand bulks more as compared to coarse sand. Extremely fine sand particularly the manufactured fine aggregate bulks as much as about 40%.
Note: Fine aggregate do not show any bulking when it is absolutely dry or completely saturated.
What Causes Bulking of Aggregate?
The moisture present in aggregate forms a film around each particle. These films of moisture exert a force, known as surface tension, on each particle. Due to this surface tension each particles gets away from each other. Because of this no direct contact is possible among individual particles and this causes bulking of the volume.
Bulking of aggregate is dependent upon two factors,
- Percentage of moisture content
- Particle size of fine aggregate
Bulking increases with increase in moisture content upto a certain limit and beyond that the further increase in moisture content results in decrease in volume. When the fine aggregate is completely saturated it does not show any bulking. Fine sand bulks more as compared to coarse sand, i.e. percentage of bulking in indirectly proportional to the size of particle.
Why to Determine Percentage of Bulking?
Due to bulking, fine aggregate shows completely unrealistic volume. Therefore, it is absolutely necessary that consideration must be given to the effect of bulking in proportioning the concrete by volume. If care is not given to the effect of bulking, in the case of volume batching, the resulting concrete is likely to be undersanded and harsh. It will also affect the yield of concrete for a given cement content.
How to Determine Percentage of Bulking?
The extent of bulking can be estimated by a simple field test.
- Fill a sample of moist fine aggregate (sand) into a measuring cylinder in the normal manner. Note down the level, say h1.
- Pour water into a measuring cylinder and completely cover the sand with water and shake it. Since the volume of the saturated sand is the same as that of the dry sand, the saturated sand completely offsets the bulking effect. Note down the level of sand, say h2.
- Subtract the final level h2 from initial level h1 (i.e. h1-h2), which shows the bulking of sand under test.
- Calculate percentage of bulking using formula given below.
- Percentage of bulking = [(h1-h2)/h2]*100
Interesting blog post! I’m curious about the benefits of bulking fine aggregate. What are they? Why is it beneficial?
Good article
Do a reference coz it is from M.S. Shetty book.
After reaching maximum level why bulking reading comes down
How bulking allowance is made in concrete batching
Good article…
When shall the test be carried out?
what is the range of bulking for a fine aggregate used for construction
2.2 to 2.6
What is the purpose of bulking of fine aggregate
Since bulking of fine aggregate is completely unrealistic, so bulking is required for proper batching
IT IS OKAY
why bulking in fine aggregates is more compared
to course aggregates?
Because fine aggregate has more surface area(surface tension) as compared to coarse aggregate.
Why bulking only in sand not in coarse aggregate
Bulking doesnt takes place in absolute dry or completely saturated aggregate
because the surface area in the fine aggregates are more as compared to the coarse aggregates .if the surafce area increases then surface tension also increases…….therefore the bulking of sand is more as compared to the coarse aggregate
thanks
Really helpful
Sir…it’s very nice and helped me a lot for my interview preparation…
Lucid to understand….
Thanks a lot…
Very useful thank you
Thank u it is too helpful to me
thanks it help me to finished my lab report.
Good help full to me