Concrete Production and Curing Questions and Answers

Q: The minimum clear (nominal) covers (in mm) to the main steel bars in footing, column, beam and slab are respectively-

The covers are 50, 40, 25, 20 mm for footing, column, beam and slab.IS 456 requires a minimum of 50 mm cover in footings, because they are in contact with soil, and 40 mm to the longitudinal bars of columns. For beams and slabs under mild exposure, the usual values in design practice are 25 mm and 20 mm respectively.The options starting with 75 mm overstate the footing value, 35 mm is not a standard beam cover, and the first option's 20 mm for beams is below the 25 mm conventionally used for main beam bars.

Q: Inadequate compaction during concrete casting results in-

Inadequate compaction results in Honey combing.When concrete is not properly compacted, entrapped air is not driven out and the mortar does not fill the spaces between coarse aggregate, leaving a rough surface full of voids that looks like a honeycomb. It reduces strength and exposes reinforcement to corrosion.Bleeding is water rising to the surface, and segregation is the separation of coarse aggregate from mortar; both result mainly from a poor mix, excess water or over-vibration rather than too little compaction.

Q: Method of curing of concrete recommended for rapid gain of strength of concrete is:

The method for rapid gain of strength is High-pressure steam curing.In high-pressure steam curing (autoclaving), concrete products are cured in steam at around 175°C and 8 to 10 atmospheres. The high temperature speeds up hydration so much that concrete reaches in about a day the strength normal curing would give in 28 days, and it also improves resistance to sulphates and reduces shrinkage. It is used for precast products.Sprinkling water and membrane curing only keep the concrete moist at ordinary temperature, so strength develops at the normal rate. Infrared radiation curing is a form of accelerated curing used in cold regions, but it is not the standard method recommended for rapid strength gain.

To avoid the segregation in concrete, it should not be dropped from a height of more than ______ while placing.

A.1 m
B.1.5 m
C.2 m
D.2.5 m

Exam Year(s)

DSSSB JE - 2023,

Answer: B

To avoid segregation, concrete should not be dropped from a height of more than 1.5 m while it is placed. A greater free fall lets the coarse aggregate separate from the mortar. When the depth to be filled is greater, concrete is lowered through a vertical chute, a tremie or an elephant trunk. The values of 1 m, 2 m and 2.5 m are not the limits adopted in the usual codes of practice.

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The minimum clear (nominal) covers (in mm) to the main steel bars in footing, column, beam and slab are respectively-

A.50, 40, 20, 20
B.50, 40, 25, 20
C.75, 40, 35, 20
D.75, 40, 25, 15

Exam Year(s)

RSMSSB JE - 2025, RSMSSB JE Agriculture - 2025, RSMSSB - 2025,

Answer: B

The covers are 50, 40, 25, 20 mm for footing, column, beam and slab.

IS 456 requires a minimum of 50 mm cover in footings, because they are in contact with soil, and 40 mm to the longitudinal bars of columns. For beams and slabs under mild exposure, the usual values in design practice are 25 mm and 20 mm respectively.

The options starting with 75 mm overstate the footing value, 35 mm is not a standard beam cover, and the first option's 20 mm for beams is below the 25 mm conventionally used for main beam bars.

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Inadequate compaction during concrete casting results in-

A.Bleeding
B.Honey combing
C.Segregation
D.Bleeding and Segregation

Exam Year(s)

RSMSSB JE - 2025, RSMSSB JE Agriculture - 2025, RSMSSB - 2025,

Answer: B

Inadequate compaction results in Honey combing.

When concrete is not properly compacted, entrapped air is not driven out and the mortar does not fill the spaces between coarse aggregate, leaving a rough surface full of voids that looks like a honeycomb. It reduces strength and exposes reinforcement to corrosion.

Bleeding is water rising to the surface, and segregation is the separation of coarse aggregate from mortar; both result mainly from a poor mix, excess water or over-vibration rather than too little compaction.

Discuss in Forum

Method of curing of concrete recommended for rapid gain of strength of concrete is:

A.Sprinkler water
B.High- pressure steam curing
C.Membrane curing
D.Infrared radiation curing

Exam Year(s)

RSMSSB JE - 2025, RSMSSB - 2025,

Answer: B

The method for rapid gain of strength is High-pressure steam curing.

In high-pressure steam curing (autoclaving), concrete products are cured in steam at around 175°C and 8 to 10 atmospheres. The high temperature speeds up hydration so much that concrete reaches in about a day the strength normal curing would give in 28 days, and it also improves resistance to sulphates and reduces shrinkage. It is used for precast products.

Sprinkling water and membrane curing only keep the concrete moist at ordinary temperature, so strength develops at the normal rate. Infrared radiation curing is a form of accelerated curing used in cold regions, but it is not the standard method recommended for rapid strength gain.

Discuss in Forum

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