Building Materials

21. Early attainment of strength in rapid hardening cement is mainly due to

1. Gypsum
2. Finer grinding
3. Tri-calcium silicate
4. Tri-calcium aluminate

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22. Excess of alumina in brick earth makes the brick

1. Impermeable
2. Brittle and weak
3. To lose cohesion
4. To crack and warp on drying

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23. First class timber has an average life of

1. Less than one year
2. 1 to 5 years
3. 5 to 10 years
4. More than 10 years

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24. For sanitary pipes and chemical stonewares,

1. Salt glazing is used
2. Lead glazing is used
3. Opaque glazing is used
4. None of these

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25. For testing compressive and tensile strength of cement, the cement mortar is made by mixing cement and standard sand in the proportions of

1. 1.2
2. 1.3
3. 1.4
4. 1.6

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26. For testing compressive strength of cement, the size of cube used is

1. 50 mm
2. 70.6 mm
3. 100 mm
4. 150 mm

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27. For the manufacture of Portland cement, the proportions of raw materials used, are

1. Lime 63% ; silica 22% ; other ingredients 15%
2. Lime 22% ; silica 63% ; other ingredients 15%
3. Silica 40% ; lime 40% ; other ingredients 20%
4. Silica 70% ; lime 20% ; other ingredients 10%

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28. Good quality stones must

1. Be durable
2. Be free from clay
3. Resist action of acids
4. All the above

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29. Gypsum consists of

1. H₂S and CO₂
2. CaSO4 and H₂O
3. Lime and H₂O
4. CO₂ and calcium

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30. Hydraulic lime is obtained by

1. Burning of lime stone
2. Burning of kankar
3. Adding water to quick lime
4. Calcination of pure clay

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