Test on bricks
The following laboratory
tests may be done to ascertain the suitability of bricks:
(i) Crushing Strength
(ii) Absorption
(iii) Shape and Size
(iv) Inflorescence.
(i) Crushing Strength:
A brick sample is immersed in water for 24 hours. The brick frog is filled with
1:3 cement mortar and the sample is placed in a moist jute bag for 24 hours and
then immersed in clean water for 24 hours. The specimen is placed in a
compression testing machine with 6 mm plywood at the top and bottom to obtain
uniform load on the specimen. The load is then applied axially at a uniform rate
of 14 N/mm2. The crushing load is noted. Then the crushing strength is the
ratio of the crushing load to the brick loaded area. The average crushing power
of five samples is taken as.
(ii) Absorption Test:
The brick sample is dried and weighed. They are then immersed in water for a
period of 24 hours. The sample is removed and wiped with a cloth. The weight of
each sample is determined in the wet state. The difference in weight reflects
the water absorbed. Then the percentage absorbance is the ratio of absorbed
water to dry weight multiplied by 100. An average of five samples are taken.
This value should not exceed 20 percent.
(iii) Size and Shape: The bricks should
be of standard size and the sides should be rectangular with sharp edges. To
test this, 20 bricks are chosen at random and they are stacked along the
length, along the width and then along the height. For standard bricks of size
190 mm × 90 mm × 90 mm. IS Code allows the following limitations:
By length: 3680 to 3920
mm
By width: 1740 to 1860
mm
By height: 1740 to 1860
mm.
The following field
tests help in locating good quality bricks:
(i) Uniformity in size
(ii) Uniformity in color
(iii) Structure
(iv) hardness test
(v) sound test
(vi) Strength test.
(i) Uniformity in Shape:
A good brick should have a rectangular flat surface and uniform in size. This
is done by observation in the check field.
(ii) Uniformity in Colour:
A good brick will have uniform colour. This observation can be made before
buying a brick.
(iii) Structure:
Some bricks can be broken in the field and their cross-section can be seen. The
section should be homogeneous, compact and free from defects such as holes and
lumps.
(iv) Sound Test:
If two bricks are struck together they should produce a clear ringing sound.
The sound should not be monotonous.
(v) Hardness Test:
A simple field test for this is to scrape the brick with a nail. If there is no
mark on the surface, the brick is hard enough
(vi) Efflorescence:
Presence of alkali in brick is not desirable as they absorb moisture to form
brown powdery patches. Hence to determine the presence of alkali this test is
done as mentioned below:
Place the brick sample
in a glass vessel containing water to a depth of 25 mm in a well-ventilated
room. Water again to a depth of 25 mm after all the water has been absorbed or
evaporated. Inspect the bricks for white/grey patches after the second
evaporation. Observations are reported as meaning 'zero', 'slight', 'moderate',
'heavy' or severe
(a) Zero: no
patch
(b) Minor: 10%
area covered with deposit
(c) Medium: 10 to
50% of the area is covered with deposits but unaccounted for with surface
layer.
(d) Heavy: More
than 50 percent of the area is covered by deposits but not with a layer of
surface.
(e) Serious: Heavy deposition of salt along the surface layer.