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21.

The cement concrete in which high compressive stresses are artificially induced before its actual use, is called

A.	plain cement concrete	B.	reinforced cement concrete
C.	prestressed cement concrete	D.	lime concrete

22.

The prestressed cement concrete can take up high tensile and compressive stresses without development of cracks.

Correct

Incorrect

23.

For heat and sound insulation purposes, we shall use

A.	vacuum concrete	B.	air-entrained concrete
C.	saw dust concrete	D.	both (b) and (c)

24.

The cement concrete, from which entrained air and excess water are removed after placing it in position, is called

A.	vacuum concrete	B.	light weight concrete
C.	prestressed concrete	D.	sawdust concrete

25.

The removal of excess air after placing concrete helps in increasing the strength of concrete by

A.	15 to 20%	B.	20 to 30%
C.	30 to 50%	D.	50 to 70%

26.

The cement concrete prepared by mixing aluminium in it, is called

A.	air-entrained concrete	B.	cellular concrete
C.	aerated concrete	D.	any one of the above

27.

The light-weight concrete is prepared by

A.	mixing Portland cement with sawdust in specified proportion in the concrete	B.	using coke-breeze, cinder or slag as aggregate in the concrete
C.	mixing aluminium in the concrete	D.	none of tha above

28.

The sound absorption coefficient of light weight concrete is nearly

A.	twice	B.	three times
C.	four times	D.	six times

29.

In making precast structural units for partition and wall lining purposes, the concrete should be

A.	sawdust concrete	B.	air-entrained concrete
C.	light-weight concrete	D.	vacuum concrete

30.

Cement concrete is

permeable

impermeable