what is sand
Sand is a basic raw material used in the construction industries. It is fine aggregate having the particle size between 150 microns and 4.75 mm.
Quality of sand is as much of importance as other materials for concrete.
Testing of Sand Quality at Construction Site
Following are the tests for sand at construction site:
- Rub the sample of the sand with wet palms. Good clean sand will not stick to the hand, whereas sand with clay will stick and change the colour of the palm. You need to test it for “silt content” on site.
Silt Content Test
- Take a glass of water and add some quantity of sand and stir the mix. Now allow the mix to settle and observe it after an hour. Clean sand will settle immediately but if it forms the distinct top layer of silt than sand contains silt or clay particles.
- The thickness of the silt layer should not exceed the thickness of the sand layer by 8% , if it contain more than 8% the sand should be washed with clear water And also if fine aggregate containing more than allowable percentage of silt shall be washed so as to bring the silt content within allowable limits.
Test for Grading of sand
- The particle size grading of sand for use in mortars shall be within the limits as specified in Table and For RCC works sand has to be coarser and for plastering works(zone 4) sand has to be finer . See zones of sand for details
Where the grading falls outside the limits of any particular grading zone of sieves, other than 600 micron IS sieve, by a total amount not exceeding 5 percent, it shall be regarded as falling within that grading zone.
To find organic impurities in the sand, you should repeat the procedue of silt content test and add caustic soda (salt ) int the glass of water .If the water changes the colour to brown,then there must be some organic impurities
- The size of particles and sharpness of sand (fine aggregates) is checked by visualization. Sand should be free from organic impurities (like shell, shingle, and other impurities) or they should be in limits which are easily identified by visualization
- 1.You Should taste a pinch of sand and if it taste salty ,the salt must be present in sand and hence it should not be used at all in any construction. such sand is naturally from the river but either it is sea sand or from an area of river frequently affected by tidal water near the sea
The presence of clay in the sand effect the performance of the concrete strength. So the presence of clay in sand can be detected by doing two physical test on sand
- Take a some amount of sand in to your hand and drop it in to the glass which contain water. After drooping the sand than shake the glass. If clay is present in the sand it will make a separate layer above the water surface. So it indicate sand is not good.
- In another simple test take some amount of sand in your hand and then drop it. If sand stick in to you fingers it indicate the presence of clay in sand.