Building Materials, Third Edition

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are used to join the old and the new concrete surfaces or between the
successive concrete lifts. The examples are synthetic latex emulsions—made from natural
rubber, synthetic rubber, polyvinyl chloride.

p ™X The examples are arsenic, tin, mercury compounds, Tributyl tin acetate.

e ™X The examples are sodium pentachlorophenate. The usual dosage is 0.2 per cent by
weight of cement.

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Some of the commercial admixtures available are:

1. Accoproof, Natson’s cement water proofer, Impermo, Sigment—increase impermeability of
   concrete.


2. Trip-L-Seal—makes the concrete rapid hardening:


3. Cico—is water proofer and makes concrete rapid hardening and increases strength.


4. Feb-Mix-Admix—is water proofer, increases workability and bond.


5. Metalcrete, ferrocrete, Asionate—are surface hardeners.

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1. (a) What is concrete and how is it made?
   (b) What is curing? What is its significance?
   (c) Define water-cement ratio. How does it influence concrete strength?


2. (a) What are the various types of concrete used in the construction industry?
   (b) Describe the procedure of preparing good quality concrete.


3. (a) What are the various methods used for curing? How 28 day concrete strength can be
   predicted in one day?
   (b) What is gel-space ratio?
   (c) Describe the factors affecting strength of concrete.


4. What is maturity concept of concrete?


5. (a) What is concrete? What are the functions played by its ingredients?
   (b) Discuss the various properties of concrete.


6. (a) What is meant by workability of concrete? How is it tested in field and in laboratory?
   (b) What are the requirements of good concrete?
   (c) How nominal mix concrete is different from design mix concrete?


7. (a) What are the factors affecting workability of concrete?
   (b) Describe the various defects in concrete. What precautions should be exercised to
   prevent them?
   (c) Describe the methods of testing fresh concrete.


8. Write short notes on following:
   (a) Carbonation of concrete (b) Split tensile strenght test
   (c) Revibration (d) Maturity of concrete