Sand is one of the most important constituents of concrete. The main purpose of mixing sand (fine aggregate) in concrete is to fill the voids between Coarse aggregate. And the voids between fine aggregate is filled with cement. Sand bulks the concrete and helps to increase the workability of concrete.
Sand is formed by the weathering of rocks. Well, different regions use the variety of sands (Pit sand, River sand, Sea Sand) in construction according to the availability. A good fine aggregate used in construction should be well-graded (all particles that have almost the same size). The fine aggregate used for construction should pass 4.75mm sieve and retain on 150 microns sieve.
So mainly we perform 5 physical tests on the sand at the site
1- Clay Test.
2- Organic impurities Test.
3- Silt Test.
4- Salt Test.
5- Earthy Matters.
1- Clay Test
The presence of clay in the sand effect the performance of the concrete strength. So the presence of clay in the sand can be detected by doing two physical tests on sand
1- Take some amount of sand into your hand and drop it into the glass which contains water. After dropping the sand than shake the glass. If the clay is present in the sand it will make a separate layer above the water surface. So it indicates sand is not good.
2- In another simple test take some amount of sand in your hand and then drop it. If sand stick into your fingers it indicates the presence of clay in the sand.
2- Organic impurities Test
To detect the organic impurities in the sand, you may perform this test.
1- Take some amount of sand and drop it into the solution of sodium hydroxide or you may use the solution of caustic soda both work the same. After adding sand into the solution then shake it. If the solution colour appears to a brown it indicates the presence of organic impurities in the sand.
3- Silt Test
Basically presence of silt in the sand is very dangerous because silt reduces the strength of the concrete. To detect the silt presence we mainly perform this basic physical test on the sand.
1- Take a glass bowl and add some amount of sand into the bowl. After adding sand add some amount of water as well as salt into the bowl and then shake it well. After shaking it leave it for at least 24 hours. If silt is present it will make a separate layer above the sand layer.
4- Salt Test
To check the presence of salt in the sand we perform a very simple and easy test.
1- Take very little amount of sand and then taste it. If salts are present in sand it tastes will be salty.
5- Earthy Matters
The earthy matters are commonly mixed in the sand. So to check the presence of earthy matters in the sand we mainly perform this physical test.
1- Take some amount of sand in your hand. After taking sand to rub it by using your other hand. If light marks appear in your hand it indicates the presence of clay.
Note: These all physical test on the sand you can perform it at the site. But when your experience increases in upcoming years in construction work you can ably to check the quality of sand without using these tests.