Sand is also called as "Fine Aggregate". It is the most important constituent in the concrete. To fill the void between coarse aggregate sand (Fine aggregate) is mixed in concrete, and the voids between sand particles is filled with cement.
In different regions different varieties of sand is available, like 'Sea sand, River sand, Pit sand' etc., Based on availability we use different varieties. A good grade sand must have almost same size sand particles.
Tests to find the quality of sand:
1. Presence of excessive moisture/ Bulking of sand:
Excessive moisture content in sand causes increase in sand volume. Moisture content in sand forms a thin layer around the sand particle, due to this each particle exerts pressure on surrounding particle. Thus sand particles move away from each other and causes increase in volume.
Before using sand for construction we have to test it for bulking because more than 5% of moisture content in its volume is not suitable for construction.
Bulking of sand depends on two factors, they are
1. Fineness of sand, and
2. Moisture content percentage.
The more fine the sand, more bulking we see in it. i.e., Medium and coarse grade sand possesses less bulking than fine grade sand.
Bulking of sand increases with increase in moisture content up to some limit after that the volume decreases.
Reference: PCA Major Series 172 and PCA ST20
2. Excessive Silt (or) Clay:
A good quality of sand must process less content of Clay. Clay in sand make sand cohesive. Excessive clay in sand is find in two ways in field, they are
--> Take some dry sand into our palm and throw it, if some sand sticks to our palm then it contains clay.
--> To test in practical way, Take some water in a glass and some sand into it. Shake it thoroughly and allow it to settle. Check that any layer is formed on the surface water or not. If layer is formed we can come to conclude that clay is present in the sand. A good sand must not have more than 8% clay content.
3. Organic impurities in sand:
To test the organic compounds presence in sand we need Sodium Hydroxide solution. Take few millilitres of sodium hydroxide solution in a glass and add some sand to it and stir it well, if the color of the solution shows lighter color then there is no organic compounds present in sand. If the solution shows brown color then we can understand that organic compounds present in sand. This type of sand is not suitable for construction.