The free moisture content in fine aggregate results in bulking of volume.
Free moisture forms a film around each particle which exerts what is known as surface tension keeping the neighboring particles away from it. Similarly, the force exerted by surface tension keeps every particle away from each other.
No point contact is possible between the particles. This causes bulking of the volume.
The extent of surface tension and consequently how far the adjacent particles are kept away will depend upon the percentage of moisture content and the particle size of the fine aggregate.
The bulking increases with the increase in moisture content up to a certain limit and beyond that the further increase in the moisture content results in a decrease in the volume and at a moisture content representing saturation point, the fine aggregate shows no bulking.
Extremely fine sand and particularly the manufactured fine aggregate bulks as much as about 40 percent
Due to the bulking, fine aggregate shows a completely unrealistic volume.
Important to consider the effect of bulking, proportioning the concrete by volume.
The extent of bulking can be estimated by a simple field test.
A sample of moist fine aggregate is filled into a measuring cylinder in the normal manner. Note down the level, say h1. Pour water into the measuring cylinder and completely inundate the sand and shake it.
Note down the level of the sand say, h2. Then h2 -h1 shows the bulking of the sample of sand under test.
