ALL YOU WANT TO KNOW ABOUT FINE AGGREGATE (SAND)

ALL YOU WANT TO KNOW ABOUT FINE AGGREGATE (SAND) AS CIVIL ENGINEER 

FINE AGGREGATE (SAND):

The fine aggregate could be natural sand or crushed stone sand. The aggregate retained on a 75-micron sieve and passing through a 4.75 mm sieve is called sand.

The coarser sand that has 4.75mm and 2.36mm particles is generally not preferred for masonry and plastering but is useful for concrete work.

As per the I.S.  code, the sand for masonry and plaster should be as per the following scale in the picture.

It would  be proper for site control that the screen of hole openings of 1.94 mm provided by a steel wire mesh of 10x10 wires per inch (diameter of wire is 0.6 mm) of for masonry work

A screen of hole opening of 0.76 mm provided by a wire mesh of 24x24 wires per inch (diameter of wire is 0.3 mm) for plasterwork, is used to screen the sand before use.

Normally,  therefore screen with 4 wires per cm. Of the screen is used for masonry and 9 wires per cm for plasterwork.

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IMPURITIES IN  SAND:

It should not contain an appreciable amount of lumps of clay, mica, shale, salts, etc. that are visible to the naked eye. There could also be organic impurities like decomposed plant matter, seashells, etc., which should not be allowed.

In some areas, such as coastal areas, the fine aggregate is removed from the stream bed, and all of these impurities are present in varying amounts. Since importing sand from faraway places could be very expensive, marine sand may need to be used. Said sand must be washed in potable water in the sand washer and must not be used as such.

The maximum quantity of silt (finer particles smaller than 75 microns) can be allowed in sand up to 8% by weight or 7% by volume. If the % of fines below 75 microns is more than permissible, the sand has to be washed to bring it less than the permitted. However, if the silt is very much in excess,   it is preferable to change the source of supply.

BULKING OF SAND:

The fine aggregate, that is, the sand has a property of swelling in volume when wet. Sand when it is dry on the surface or when it is fully saturated has the least volume. The approximate adjustment required for the volume of sand to be used in the different water content of the sand is as follows:

In case the sand is moist at the time of preparing the mix, necessary adjustment i.e. an additional volume of sand be added and also the quantity of water reduced.

TESTING OF SAND:

A) Tests Done On Laboratory:  All chemical and physical properties should be tested while selecting or approving a source for sand. The tests shall be for,

1)          Grading

2)          Organic impurities

3)          Inorganic impurities

4)          Chloride content

5)          Sulphate content as SO3

6)          Silt content

B) Field Tests Done By Site Engineer

1) Determination of silt content: The sand is filled in a 250 ml measuring cylinder. capacity, up to 100 ml of brand. Clean drinking water is added up to the 150 ml mark. A pinch of common salt is added and the jar vigorously shakes 250 ml of Jar Water Silt 100 - X. The cylinder is kept on the table without discomfort and the content is left to stand for 2 hours. below and fine deposits of silt and clay impurities will reach the top. Measure the sand level, say it's X.

Silt content = (100-X) %.

2) Visual inspection for Impurities: You can see colored particles other than sand, such as shells, gravel, lime, lumps of clay, etc., while unloading the sand from the truck. Said impurities must not exceed 1% of the sand received. Much of these impurities can be removed by simple screening.

3) Bulking of sand: Take the sand into a 250 ml measuring cylinder, up to 200 ml mark. Pour water into the cylinder so that the sand is completely submerged. Stir the cylinder well. Wait about 15 minutes for the sand to settle. Measure the mark where the sand is in the cylinder, say X ml.

% bulkage of sand = {(200-X)/X}100

4) Grading: It is a good practice to check the degree of sand when it is received on-site, to avoid waste when using it. It must be ensured that all sand is screened before use. The sand used for plastering is finer and must pass through a screen with 9 holes per cm of screen length; Masonry sand must pass through a screen with 4 cables per cm of screen length. For concrete, no less than 20% of the sand must be fine passing through a 600-micron sieve.

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