Brick is the most commonly and oldest used construction material especially in building construction because of their durability, reliability, strength and low cost. Brick, before using for construction work it must be tested whether it is suitable for brickwork or not.
Tests on bricks should be conducted in at laboratory site as well as in construction site (field) if all necessary apparatus available at site (field).
Some important field tests of bricks describe below –
1. Color Inspection Test
2. Shape & Size Examination Test (Frog)
4. Soundness Test
5. Hardness Test
6. Drop Test
7. Texture and Compactness
8. Water Absorption Test
9. Crushing strength Test
10. Efflorescence Test
· A well burnt brick has a uniform colour on its surface.
· A good brick should have uniform copper colour.
· Over burnt and under burnt brick losses uniformity of colour on its surface and strength.
Hence, a good quality brick should always be of uniform colour throughout.
2) SHAPE & SIZE EXAMINATION TEST:
· Shape and size of all bricks should be uniform and same.
· The Shape of all the bricks should be plain, rectangular surfaces with parallel size and sharp edges.
· Stander size of brick consists Length x Breathe x Height as 190 mm x 90mm x 90 mm.
· A good brick should not exceed 3 mm tolerance in length and 1.5 mm tolerance in width and height.
· To check the size and shape uniformity, randomly take out 10 to 20 bricks from the group and stack them along its length, breathe and height and compare if all the bricks are same shape and size then bricks can use for construction.
· A good brick should have a proper frog of size 100 mm in length, 40 mm in width and 10 mm in depth.
3) UNWANTED MATERIAL INSPECTION:
· Brick should be free from stones, kankars, organic matter and harmful chemical etc.
4) SOUNDNESS TEST:
· Soundness test of brick shows the nature of bricks against sudden impact.
· To perform this test randomly choose some bricks and struck them with one another, a well burnt brick should give a metallic sound when struck, otherwise struck the brick with a hammer it should give a pure metallic sound then it is said to be good brick.
5) HARDNESS TEST:
· A good quality bricks should be hard enough to resist scratches against sharp thing.
· To perform this test, when a brick scratched by a finger nail or sharp tool no impression is made on the brick it is said to be a hard brick
6) DROP TEST:
· In this test, a good brick should not break when we drop it from a height of 1.2 meter to 1.5 meter on a hard surface (concrete floor) or on another brick.
7) TEXTURE AND COMPACTNESS:
· The surface of a good brick should not be too smooth causing slipping of mortar.
· A good brick, should have pre-compacted and uniform texture, and should not show cracks, holes, grits or lumps of lime.
8) WATER ABSORPTION TEST:
· This test is carried out to check the water content absorbed by the brick.
· Water absorption should not be more than 20% of its dry weight after immersion in water for 1 (one) hour. If the brick absorb water more then its allowable limit then the brick absorb water from the mortar during construction and make the break bond weaker.
· To perform this test,
a. First, weigh the dry bricks and note down it weight as W1 (Kg).
b. Second, immerse the brick into water for 1 hour.
c. Third, remove the brick from the water after 1 hour and weigh it again and note down its weight as W2 (Kg).
d. Finally,Water Absorption = (W2 – W1) / W1 X 100
· In the lab test the brick should be allowed to immerse in water for at least 24 hours. For a good brick the permissible limit of water absorption is 20 % maximum, varying based on the various brick classes.
· The water absorption of bricks after 24 hours immersion as follows –
For first class brick – 20%, second class brick – 22%, third class brick – 25%, and heavy-duty machine-made brick should not absorb more than 5% of their weight.
9) CRUSHING STRENGTH OR COMPRESSIVE STRENGTH TEST:
· The crushing strength of a brick is performed by placing a brick in compression testing machine and then load is applied on the brick until it breaks, and note down the value of failure load and find out the crushing of brick.
· The minimum compressive strength of a brick is 3.50 N/mm2, if the test result is less than 3.50 N/mm2then the brick is not useful for the construction work.
· This test is carried out on site only if the machine is available on site otherwise it is done on lab.
10) EFFLORESCENSE TEST:
· It is not a field test, but it is necessary to know –
· One can easily identify the defect by observing any white patch on brick surface.
· A good brick should not contain any soluble salts (like Sodium and Potassium), if soluble salts present in brick it will cause effloresces on brick surface.
· To know the presence of such soluble slats, a brick should be placed in water bath for 24 hours and dry in shade. If there is any white color of deposit on the surface of the brick then it contains soluble salts and the brick is not good for construction work.