Durability of Concrete important Question GATE 2025

                                Durability of Concrete important Question GATE  2025

1    Primary Ettringites are formed during hydration of cement. But sample A and B shows crack initiation after few months. The sample A is collected from a railway sleeper whereas sample B is collected from surface of a sewage pipe. What can you say about A and B?

 SO3 is penetrating from outside for sample A and B, forming external ettringite.

 External ettringite is formed in sample A, whereas delayed ettringite formation in sample B.

 SO3 is penetrating from outside for sample B forming gypsum and deteriorating CSH, whereas delayed ettringite formation is seen in sample A.

 Secondary ettringite formation is seen in sample A and B.

accepted Answers:

SO3 is penetrating from outside for sample B forming gypsum and deteriorating CSH, whereas delayed ettringite formation is seen in sample A

2. 

A: The cover depth design should be done as per the splash (tidal) zone requirement.

R: The chemical attack is accompanied with physical abrasion (waves, sand), wetting-drying cycle, and freezing thawing, and humidity gradient.  

S: The submerged zone will be subjected to saltwater spray and wetting-drying.

 A, R, and S are true, and S is correct reasoning of A and R.

 A, R, and S are true, and R is correct reasoning of S and A.

 A, R, and S are false.

 A, S are true, R is false. S is correct reasoning of A.

 A, R are true, S is false. R is correct reasoning of A.

Accepted Answers:

A, R are true, S is false. R is correct reasoning of A.

3.  

Which of the following are true?

 Carbonation leads to increase in pH due to reaction with portlandite. 

 Cementitious systems with SCMs show higher carbonation depth because of less portlandite, coarsening of pores and increasing in porosity.

 CSH reacts with carbon dioxide to form dense CaCO3 and silica gel in absence of portlandite.

 Carbonation can lead to corrosion of steel in a moisture free sealed sample.

 ASR can happen in the absence of moisture.

Accepted Answers:

Cementitious systems with SCMs show higher carbonation depth because of less portlandite, coarsening of pores and increasing in porosity.

CSH reacts with carbon dioxide to form dense CaCO3 and silica gel in absence of portlandite

4   Steel embedded in uncontaminated concrete does not corrode due to –

 Low pH of concrete pore solution and formation of layer of initial corrosion products on steel.

 High pH of concrete pore solution and formation of layer of initial corrosion products on steel.

 Formation of layer of low pH cement protecting the steel.

 Steel cannot corrode in presence of portlandite

Accepted Answer

High pH of concrete pore solution and formation of layer of initial corrosion products on steel.

5

Select the factors that have significant influence on the corrosion initiation:

 Use of waterproofing compounds in concrete

 Cracking of the cover concrete

 Type of cement used in concrete

 Use of coating on steel surface

 Type of superplasticizer used in concrete

Accepted Answers:

Cracking of the cover concrete

Type of cement used in concrete

Use of coating on steel surface1

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