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Doctors Medicines MCQs Q&A

  1. 1 and 2 only
  2. 2 and 3 only
  3. 2 and 4 only
  4. 3 and 4 only
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Option 4 : 3 and 4 only

Various defects of bricks are as follows:

a) Over-burning of Bricks: Bricks should be bummed at temperatures at which incipient, complete and viscous vitrification occur. However, if the bricks are overburnt, a soft molten mass is produced, and the bricks lose their shape.

b) Under-burning of Bricks: When bricks are not burnt to cause complete vitrification, the clay is not softened because of insufficient heat and the pores are not closed. This results in higher degree of water absorption and less compressive strength.

c) Bloating: This defect observed as spongy swollen mass over the surface of burned bricks is caused due to the presence of excess carbonaceous matter and sulphur in brick-clay.

d) Black Core: When brick-clay contains bituminous matter or carbon and they are not completely removed by oxidation, the brick results in black core mainly because of improper burning.

e) Efflorescence: This defect is caused because of alkalies present in bricks. When bricks come in contact with moisture, water is absorbed, and the alkalis crystalize. On drying grey or white powder patches appear on the brick surface.

f) Chuffs: The deformation of the shape of bricks caused by the rainwater falling on hot bricks is known as chuffs.

g) Checks or Cracks: This defect may be because of lumps of lime or excess of water. the absorbed water reacts with lime nodules causing expansion and a consequent disintegration of bricks, whereas shrinkage and burning cracks result when excess of water is added during brick manufacturing.

h) Spots: Iron sulphide, if present in the brick clay, results in dark surface spots on the brick surfaces. Such bricks though not harmful are unsuitable for exposed masonry work.

i) Busters: Broken blisters are generally caused on the surface of sewer pipes and drain tiles due to air imprisoned during their molding.

Sulphate attack on brick masonry:

In brick masonry, the excess sulphate reacts with tricalcium aluminate to form the compound sulfo-aluminate. The compound expands to form crack in the mortar joints, followed by gradual deterioration.

Such expansion leads to leaning and bulging and results in the instability of the brick work.

The face of the joint spalls and the mortar cracks and gambles.

∴ The above said defect is caused due to efflorescence and sulphate attack on the brick and brick masonry.

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Related Questions

In the following question, the 1st and the last part of the sentence/passage are numbered 1 and 6. The rest of the sentence/ passage is split into four parts and named P, Q, R and S. These four parts are not given in their proper order. Read the sentence/ passage and find out which of the four combinations is correct. 1. Customers of collapsed tour operator Thomas Cook have been getting in touch with the BBC to voice their frustration at delays in processing their refunds for holidays that never took place. P. Retired teachers Alan and Diane Holmes from Ripon in north Yorkshire booked a two-week holiday in Egypt, but initially thought their money was safe because the booking was made through another firm, Freedom Holidays. Q. The Civil Aviation Authority (CAA) originally said all valid claims made on the first day of its refund programme would be paid within 60 days, or by Friday 6 December. R."My wife always wanted to do the Egypt Nile cruise. It's been quite peaceful there these last two years, so we thought we'd best do it before it all takes off again," Mr Holmes told the BBC, referring to the possibility of civil unrest in the country. S. But now it says only two-thirds will be paid on time. 6. But as they later found out, the cruise itself and the hotel accommodation had been booked through Thomas Cook.?
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