Consider the following statements with respect to rigid pavements:
Statement-1: Bottom-up cracking (BUC) in rigid pavements is caused at the edge of the slab due to combined effect of single or tandem rear axle load and positive temperature differential.
Statement-2: Top-down fatigue cracking (TDC) in rigid pavements is caused due to repeated cycles of axle loads and negative temperature differential.
The CORRECT option is:

Question

What is the CORRECT match between the air pollutants and treatment techniques given in the table

Air Pollutants		Treatment techniques
P	NO₂	i	Flaring
Q	SO₂	ii	Cyclonic separator
R	CO	iii	Lime scrubbing
S	Particles	iv	NH₃ injection

Answer 1

This question checks whether you can connect each type of rigid pavement crack to the specific combination of load and temperature that causes it. Let's look at each statement on its own.

Statement-1 (bottom-up cracking): during the day, the top surface of a concrete slab warms up faster than the bottom, so the slab tries to curl its edges downward. A heavy single or tandem axle load parked near the edge at this time adds extra bending on top of that curling, and the combination stretches the concrete fibres at the bottom of the slab the most. Cracks that start from these bottom fibres and work upward are called bottom-up cracks, and this is exactly what Statement-1 says, so it holds up as TRUE.
Statement-2 (top-down cracking): at night, the top surface cools faster than the bottom, so the slab edges curl upward instead, losing some of their support right at the edge. A heavy axle repeatedly rolling over this lifted edge stretches the concrete fibres at the top the most, and cracks starting from the top and working down are called top-down cracks. This matches Statement-2 exactly, so it also holds up as TRUE.

Since both descriptions line up correctly with day and night curling and where the resulting tensile stress peaks (bottom fibre for the daytime case, top fibre for the nighttime case), neither statement contains an error.

Let's summarize:

Positive (daytime) temperature differential plus edge axle load gives bottom-up cracking.
Negative (nighttime) temperature differential plus repeated edge axle load gives top-down cracking.

So the correct choice is the option stating both statements are TRUE.

Answer 2

This question checks whether you can connect each type of rigid pavement crack to the specific combination of load and temperature that causes it. Let's look at each statement on its own.

Statement-1 (bottom-up cracking): during the day, the top surface of a concrete slab warms up faster than the bottom, so the slab tries to curl its edges downward. A heavy single or tandem axle load parked near the edge at this time adds extra bending on top of that curling, and the combination stretches the concrete fibres at the bottom of the slab the most. Cracks that start from these bottom fibres and work upward are called bottom-up cracks, and this is exactly what Statement-1 says, so it holds up as TRUE.
Statement-2 (top-down cracking): at night, the top surface cools faster than the bottom, so the slab edges curl upward instead, losing some of their support right at the edge. A heavy axle repeatedly rolling over this lifted edge stretches the concrete fibres at the top the most, and cracks starting from the top and working down are called top-down cracks. This matches Statement-2 exactly, so it also holds up as TRUE.

Since both descriptions line up correctly with day and night curling and where the resulting tensile stress peaks (bottom fibre for the daytime case, top fibre for the nighttime case), neither statement contains an error.

Let's summarize:

Positive (daytime) temperature differential plus edge axle load gives bottom-up cracking.
Negative (nighttime) temperature differential plus repeated edge axle load gives top-down cracking.

So the correct choice is the option stating both statements are TRUE.

Show Hint

The Correct Option is A

Solution and Explanation

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