GATE Civil Engineering (CE) 2019 Shift 2 Solved Paper

Question : 59 of 65

Marks: +1, -0

In the context of provisions relating to durability of concrete, consider the following assertion
Assertion (1): As per IS 456-2000, air entrainment to the extent of 3% to 6% is required for concrete exposed to marine environment.
Assertion (2): The equivalent alkali content (in terms of Na2O equivalent) for a cement containing 1% and 0.6% of Na2O and K2O, respectively, is approximately 1.4% (rounded to 1 decimal place)
Which one of the following statements is correct?

Assertion (1) is true and Assertion (2) is FALSE
Both Assertion (1) and Assertion (2) are TRUE
Both Assertion (1) and Assertion 2) are FALSE
Assertion (1) is false and Assertion (2) is TRUE

Validate

Solution:

As per IS-456, where freezing and thawing actions under wet conditions exit, inhance durability can be obtained by the use of suitable air entraining admixture.
The entrained air percentage can vary from

4 ± 1

5 ± 1

(i.e. 3 to 6%) depending on size of aggregate. Hence, Assertion (1) is correct.
Equivalent alkali content (in terms of

{Na}_{2} {O}

equivalent)

= {Na}_{2} {O}+0.658 × {K}_{2} {O}

Molecular ratio of

{Na}_{2} {O}

{K}_{2} {O}=0.658

=1 \%+0.658 × 0.6 \%=1.39

≃ 1.4

(rounded to 1 decimal place).

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