Ce cement - explain comprehensive PDF

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MEA ENGINEERING COLLEGE DEPARTMENT OF CIVIL ERNGINEERING, MATERIAL FOR COMPREHENSIVE EXAMINATION 1. Why is natural cement used very limitedly? a) Brown in Colour b) Standard consistency is not met with c) Sets too quickly d) Particle size is too fine Answer: c Explanation: Natural cement sets very quickly after addition of water and hence it is not quite workable. Artificial cement is preferred over this. 2. What is the average particle size of cement? a) 15 microns b) 45 microns c) 75 microns d) 100 microns Answer: a Explanation: Approximately 95% of cement particles are smaller than 45 microns and the average particle size is 15 microns. 3. What is the meaning of soundness of cement? a) Ability to flow when mixed b) Ability to make ringing noise when struck c) Ability to form strong and sound structure d) Ability to retain volume after setting. Answer: d Explanation: When cement paste hardens and sets, it should not undergo any volume change. Soundness ensures this and is tested using Autoclave expansion test. 4. Time elapsed from the instance of adding water until paste ceases to behave as fluid is called: a) Initial setting time b) Final setting time c) Intermediate setting time d) Absolute setting time

Answer: a Explanation: Final setting time is the time required for cement paste to reach certain state of hardness. 5. Which of the below mentioned is not a result of field test performed on cement? a) There should not be any lumps b) It should feel cold when you put your hand in bag of cement c) The colour should be blackish grey d) It should not be gritty when rubbed with finger Answer: c Explanation: The colour of cement is normally grey with a greenish tint. There are different shades – lighter and darker, but it does not go as dark as blackish grey. 6. Which equipment is used to test setting time of cement? a) Core cutter b) Vibrator c) Universal testing machine (UTM) d) Vicat apparatus Answer: d Explanation: Core cutter is used to determine dry density of soil. Vibrator is used in sieve analysis. UTM can be used to test various parameters – tension, bending, shear of various materials. Vicat apparatus consists of a needle, used to penetrate the cement paste sample. 7. What is the initial setting time of cement? a) 1 hour b) 30 minutes c) 15 minutes d) 30 hours Answer: b Explanation: As per IS code 4031-part 5, the initial setting time of cement is minimum of 30 minutes. After this cement will start losing its plasticity and will not be workable. 8. Use of coarser cement particles leads to: a) Low durability b) Higher strength c) Low consistency d) Higher soundness Answer: a Explanation: For coarser particles, hydration starts on surface of particles, hence, it might not be completely hydrated. This causes low strength and low durability.

9. Wet cement can cause severe skin burns if not washed off with water immediately. a) True b) False Answer: a Explanation: Cement is highly alkaline and setting process is exothermic. Wet cement is strongly caustic and causes skin burns. Similarly, dry cement causes eye or respiratory irritation, when it comes in contact with mucous membranes. 10. Green cement is: a) Green coloured cement b) Cement mixed with plant products c) Cement mixed with recycled materials d) Cement mixed with green alga Answer: c Explanation: Green cement is a cementitious material which employs the use of optimized recycled materials. These can meet or even exceed the functional performance of Portland cement. 11. What is the depth the needle in Vicat apparatus should penetrate into the cement paste in consistency test? a) 33-35 cm from bottom of mould b) 33-35 mm from top of mould c) 33-35 cm from top of mould d) 33-35 mm from bottom of mould Answer: b Explanation: The best procedure has been clearly mentioned in IS 4031 Part 4. According to the code, 33-35mm depth of penetration is ideal. 12.What is the most dominant constituent of cement? a) Silica b) Lime c) Magnesia d) Alumina Answer: b Explanation: Cement contains about 60-65% of lime. Silica constitutes 17-25%, alumina 3-8% and magnesia 1-3%.

13. Deficiency of lime in cement leads to: a) Unsound cement b) Disintegration of cement c) Quick setting of cement d) Expansion of cement Answer: c Explanation: Presence of lime in sufficient quantity is necessary to form silicates and aluminates of calcium. Excess lime leads to expansion, disintegration and unsoundness of cement. 14. What effect does calcium sulphate have on cement? a) Retards setting action b) Acts as flux c) Imparts colour d) Reduces strength Answer: a Explanation: Calcium sulphate is found in cement in the form of gypsum. Its slows down the setting time of cement. 15. Which of the following adds quick-setting property to cement? a) Magnesium oxide b) Silicon dioxide c) Iron oxide d) Aluminium oxide Answer: d Explanation: Aluminium Oxide or Alumina is present in small quantity in cement and it helps in quick-setting property. 16. Excess of Alkali in cements results in: a) Dry cement paste b) Efflorescence c) Less plasticity d) Unsound cement Answer: b Explanation: Efflorescence is the formation of powdery substance on the surface of masonry or concrete work. Alkalis usually get carried away by flue gases during heating. In excess quantity, they result in alkaliaggregate reaction.

17.. What function does iron oxide perform in cement? a) Increases strength b) Makes cement sound c) Increases setting time d) Acts as flux View Answer Answer: d Explanation: Iron oxide acts as flux, in addition to being responsible for imparting colour to cement. If temperature goes higher, then iron oxide reacts with aluminium and calcium and results in formation of calcium aluminate ferrite. 18. How many major ingredients are present in the composition of cement? a) 8 b) 5 c) 10 d) 6 View Answer Answer: a Explanation: There are 8 main ingredients present in cement. They are lime, silica, alumina, magnesia, iron oxide, calcium sulphate, sulphur trioxide and alkalis. 19. Sulphur in cement is present in what amount? a) 0.5 – 6 g b) 1 – 2.5% c) 0.5 – 6% d) 1 – 2.5g View Answer Answer: b Explanation: The presence of ingredients is expressed in percentage. Iron oxide is present in 0.5-6% and sulphur 1-2.5%. 20. An excess of magnesium oxide after 5% is harmful to cement. a) True b) False View Answer Answer: a Explanation: Excess of magnesium causes problems in structures built with this cement. It causes cracks in both mortar and concrete after they harden...