The crushing affords a basis for comparing the quality of bricks but is of little value in determining the strength of a masonry wall, since the latter depends primarily on the strength of mortar.
Testing Of Bricks:
Compressive Strength Test (IS: 3495 (Part I))
The
crushing affords a basis for comparing the quality of bricks but is of
little value in determining the strength of a masonry wall, since the latter
depends primarily on the strength of mortar. Six bricks are taken for the
compressive strength test althought it may be found that an individual brick
varies by 20% or more from the average, the permissible stresses allowed for
load bearing walls take account of this, being based on an average strength of
six bricks. It is, therefore, both unnecessary and uneconomical to insist that
every bricks is above a certain strength. As a criterion of structural strength
for brick, the transverse failure in a wall or pavement is likely to occur on
account of improper bedment. For testing bricks for compressive strength from a
sample the two bed faces of bricks are ground to provide smooth, even and
parallel faces. The bricks are then immersed in water at room temperature for
24 hours. These are then taken out of water and surplus water on the surfaces
is wiped off with cotton or a moist cloth. The frog of the brick is flushed
level with cement mortar and the brick is stored under damp jute bags for 24
hours followed by its immersion in water at room temperature for three days.
The specimen is placed in the compression testing machine with flat faces
horizontal and mortar filled face being upwards. Load is applied at a uniform
rate of 14 N/m^{2} per minute till failure. The maximum load at failure
divided by the average area of bed face gives the compressive strength.
Compressive
strength (N/mm^{2})
= M aximum load at failure (N) / A verage area
of bed faces (mm)
average
of results shall be reported. The compressive strength of any individual brick
tested in the sample should not fall below the minimum average compressive
strength specified for the corresponding class
of brick by
more than percent.