Compressive /Crushing Strength of Bricks
Compressive /Crushing strength of bricks (Indian Made) are very variable, and may vary from 30 kg/sq. cm to 150 kg/sq. cm for hand-made burnt bricks, while Crushing strength of heavy duty bricks machine pressed (also called engineering bricks) may have compressive strength as high as 450 kg/sq. cm, and even 500 kg/sq. cm. The minimum crushing / compressive strengths of burnt bricks tested flat-wise prescribed are:
(i) Common building bricks—35 kg/sq. cm,
(ii) Second class bricks—70 kg/sq. cm,
(iii) First class bricks— 105 kg/sq. cm.
(iv) Crushing strength of bricks not less than 140 kg/sq. cm are graded as AA class.
The strength of bricks decreases by about 25 per cent when soaked in water.
Strength of sun-dried (unburnt) bricks is from 15 to 25 kg/sq. cm.
Water absorption of bricks after 24 hours immersion,
First class bricks—20%,
Second class bricks—22 %,
Third class bricks—25%.
Heavy duty machine made bricks should not absorb more than 5% of their weight.