Tests of brick

Tests for bricks

A brick is generally subjected to the following tests to find out its suitability for the construction works:

(1)    Absorption

(2)    Crushing strength

(3)    Hardness

(4)    Shape and Size

(5)    Soundness

(6)    Structure

(7)    Presence of soluble salts

(1)    Absorption

A brick is taken and it is weighed dry. It is then immersed in water for a period of 24 hrs. It is weighed again and the difference in weight indicates the amount of water absorbed by the brick. It should not, in any case, exceed 20% of weight of dry brick.

(2)    Crushing strength

The crushing strength of a brick is found out by placing it in a compression testing machine. It is pressed till it breaks. As per BIS: 1077-1957, the minimum crushing strength of bricks is 3.5 N/mm². The bricks with crushing strength of 7 to 14 N/mm²are graded as A and those having  above 14 N/mm² are graded as AA.

(3)    Hardness

In this test, a scratch is made on brick surface with the help of a finger nail. If no impression is left on the surface, the brick is treated as hard.

(4)    Shape and Size

In this test, a brick is closely inspected. It should be of standard size and its shape should be rectangular with sharp edges. For this purpose, 20 bricks of standard size (190 x 90 x 90 mm) are selected at random and they are stacked lengthwise, widthwise and height wise.

For good quality bricks, the results should be within the following permissible limits: Length: 3680 to 3920 mm

Width: 1740 to 1860 mm

Height: 1740 to 1860 mm

(5)    Soundness

In this test, the two bricks are taken and they are struck with each other. The bricks should not break and a clear ringing sound should be produced.

(6)    Structure

A brick is broken and its structure is examined. It should be homogeneous, compact and free from any defects such as holes, lumps etc.

(7)    Presence of soluble salts:

The soluble salts, if present in bricks, will cause efflorescence on the surface of bricks. For finding out the presence of soluble salts in a brick, it is immersed in water for 24 hrs. It is then taken out and allowed to dry in shade. The absence of grey or white deposits on its surface indicates absence of soluble salts.

If white deposits cover about 10% surface, the efflorescence is said to be slight and it is considered as moderate, when the white deposits cover about 50% of surface. If grey or white deposits are found on more than 50% of surface, the efflorescence becomes heavy and it is treated as serious, when such deposits are converted into powdery mass.



** basic civil engineering notes for bput students.