The
following field tests may be conducted to ascertain
the quality of cement.
a) The colour should be uniform.
b) The cement should feel smooth when touched or
rubbed in between fingers.
c) The Cement should be cool when hand is thrust
through inside heap/bag of cement.
d) Small quantity of cement thrown over a bucket of
water should sink and not float on surface.
e) A thin paste of cement with water should feel
sticky between fingers.
f) The cement should not contain hard lumps.
g) A sample of cement is taken and heated on a clean
steel plate kept on a stove for about 20 mins. A
change in color in cement indicates adulteration
with stone dust.
h) A sample of cement is put in half glass full of
water and stirred well and allowed to settle. It
will leave the adulteration in cement to continue to
float.
Storage of Cement
Cement has a tendency to absorb moisture. If the
moisture absorption exceeds 5%, the cement becomes
useless. Hence cement should be stored as for as
possible in air tight containers. It is not
advisable to store cement in jute bags for more than
3 months. The cement should be stacked in piles of
10 bags each and 30 cms away from the external wall.
Top and bottom of stacks should be covered with
tarpaulins. In spite of every precaution taken in
storage of cement certain loss of strength with the
passing of time is inevitable as shown below:
Fresh Cement - 100 % strength
After 3 month - 20 % less strength.
After 6 month - 30 % less strength.
After 12 month - 40 % less strength.
After 24 month - 50 % less strength.
2. AGGREGATES
2.1 Fine Aggregate (Sand)
Sand is generally obtained from beds of rivers
and streams. They are generally found clean and is
widely used. Sand is classified according to the
size of grains:
a. Fine sand passes through a screen of 1.587 mm
opening. This is mainly used for plastering.
b. Coarse sand passes through a screen of 3.175 mm.
This is mainly used for masonry work.
c. Gravelly sand passes through a screen of 7.162 mm
and is used for concrete works.
The following field test can be carried out to
ascertain fitness of sand
a. A sample of sand is taken and rubbed in hand. If
clay content is more, it leaves soil on hand and
such sand should be rejected.
b. When sand is watered and dried, if it leaves
white salt or when tasted salty, the same is not
suitable.
c. A solution of Sodium Hydroxide or Caustic Soda is
added to the sand and stirred. The solution changes
its color to brown if organic matter is present.
Such sand is not fit for construction.
d. The sand shall be clean, coarse and angular and
free from vegetable and organic matter.
2.2. Coarse Aggregate
Coarse aggregate is the material used as filler
in cement concrete mix and are formed by crushed
stones either mechanically or manually.
a. The crushed stone should consist of clean angular
fragments uniform in size. It should be free from
elongated pieces, soft or disintegrated stones or
clay.
b. Rounded particles do not provide good
interlocking. Hence they should be rejected.
c. Aggregate should not contain harmful materials
such as iron pyrites, coal, mica, shale or similar
laminated material, clay, alkali, sea shells organic
impurities.
3. BRICKS
The following visual tests and field tests be
carried out to ascertain good quality bricks for use
in works.
a. Well burnt bricks are copper colored and are free
from cracks.
b. They posses sharp and square edges.
c. They are of uniform color, shape and size as per
standard.
d. When struck with each other, they produce clear
metallic ringing sound.
e. Fracture of good bricks show uniform and bright
compact structure without any voids.
f. They absorb minimum water when immersed in water.
The absorption should not be more than 20 % when
immersed in water for 24 hours.
g. Good bricks are hard on their surface and leave
no impression when scratched with nails.
h. Good bricks do not break when dropped from 1 m
height
i. Good bricks when soaked in water and dried, do
not show white patches or white deposits on their
surface.
j. The good quality bricks could be gauged easily by
the percentage of bricks that get broken in transit
and stacking in the course of ordinary handling (2
to 3%).
4. STEEL
The mild steel / TOR steel used in RCC works should
be
a. Able to develop good bond with concrete
b. Should have thermal expansion nearer to concrete.
c. Should have high tensile strength.
d. Should not get affected by concrete.
e. Should afford easy cutting, bending and welding.
f. It should be ensured that the bars used are clear
and free from dust or rust.
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