6. A. Which of the following types of masonry generates its shearing resistance
ID: 1732731 • Letter: 6
Question
6. A. Which of the following types of masonry generates its shearing resistance from the interaction between fired clay bricks and cement-based mortar? i. Stretcher bond ii. Dry stone iii Adobe. iv. CMU walling [2 marks] B. Why is mild steel used instead of stainless steel as reinforcement in concretes? i. Mild steel is cheaper, and less dense ii. Mild steel has higher flexural strength, and the alkaline conditions inside concrete a protective passivation layer which reduces its corrosion. iii. The alkaline conditions inside concrete produce a protective passivation layer which reduces corrosion of mild steel, and it is cheaper Mild steel has a lower elastic modulus, and a higher flexural strength. iv. [2 marks] C. Why does toughened glass withstand more flexural load than untreated glass? i. Because it contains more sodium oxide which improves its strength. ii. Because its surface is held in tension which prevents cracks from forming iii. Because its surface is held in compression which restricts cracking iv. Because it has a thin polymeric layer which reinforces the brittle glass [2 marks] D. Which of the following is classified as a supplementary cementitious material? i. Coarse aggregate 11. Fine aggregate ii. Portland cement. iv. Ground limestone [2 marks]Explanation / Answer
(A) option i is correct because stretcher bond is only the brick masonry bond among the given options.Adobe bricks are only sun dried and not kiln fired. CMU is concrete masonry unit.
(B)option iii is corect. Although stainless steel is much more corrosion resistant but use of stainless steel in reinforcement will be highly uneconomical as the cost of machining of stainless steel is very high.Moreover stainless steel is itself costlier. Mild steel also becomes corrosion resistant while being used as reinforcement due to the formation of passive layer because of alkaline conditions in concrete.
(C) option iii is correct.Toughened glass also called tempered glass has its outer surface in compression by controlled thermal and chemical treatment processes to increase its strength compared to normal glass.Such stresses cause the glass to crumble into small granular chunks which are less likely to cause injury.
(D)option iv is correct.Supplementry cementitious materials are those materials which are added to concrete mixtures to make mixture more economical, less permeable,increase strength due to their hydraulic or pozzolanic activity.They can be individually used with portland cement.
(F) option iv is correct. It measures resistivity of concrete.RCP test measures the electrical indication of ability of concrete to resist penetration of chloride ion.
(G)option iii is correct.Hydaulic cement sets and gets hardened under water conditions.
(H)Option ii is correct.Porosity and strength affect the freeze thaw durability of brick or concrete due to the penetration of water which expands on freezing and conracts in volume upon thawing and hence affects the durability.
(I)option iv is correct.External sulphate attack is due to penetration of sulphates in solution while Internal sulphate attack is due to a soluble source being included in concrete at the of mixing etc.
(J)option iii is correct. Polyurethane is most water resistant.It makes wood waterproof.
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