Question

Which of the below is not a type of force acting on the cement concrete pavement?

• A. Environmental changes
• B. Drying shrinkage
• C. Traffic load
• D. Ductile load

Hint:

Pavement design considers various stresses:

• Load Stresses: Due to traffic (flexural, shear, bearing).
• Warping Stresses: Due to temperature differential across slab depth.
• Frictional Stresses: Due to temperature expansion/contraction resisted by subgrade friction.
• Shrinkage Stresses: Due to drying and subsequent contraction of concrete.

Understanding material properties (brittle vs. ductile) is key to identifying incorrect terminologies.

Answer 1

The Correct Option is D

Step 1: Understand forces acting on cement concrete pavements.
Cement concrete pavements (rigid pavements) are subjected to various forces and stresses that can cause distress and affect their performance. These forces can be broadly categorized into traffic-induced stresses and environmental stresses.
Step 2: Analyze each option as a potential force/stress.

• (1) Environmental changes: This refers to stresses induced by changes in temperature and moisture.
  • Temperature changes: Cause expansion and contraction of the concrete slab, leading to curling and warping stresses, and also frictional stresses at the interface with the subgrade.
  • Moisture changes: Cause swelling and shrinkage of the concrete, similar to temperature effects.
  So, environmental changes induce significant forces/stresses.
• (2) Drying shrinkage: This is a specific type of stress induced by moisture changes. As concrete dries, it shrinks, and if this shrinkage is restrained (e.g., by the subgrade or internal friction), it induces tensile stresses within the pavement, potentially leading to cracking. This is a real force/stress.
• (3) Traffic load: This refers to the dynamic and static forces exerted by vehicles on the pavement. These loads cause flexural stresses, shear stresses, and bearing stresses in the concrete slab, leading to fatigue and structural damage over time. This is a primary force.
• (4) Ductile load: "Ductile load" is not a recognized type of force or stress acting on cement concrete pavements. Ductility is a material property that describes its ability to deform under tensile stress without fracturing (i.e., to undergo plastic deformation). Concrete is a brittle material, not ductile. While it experiences loads, the term "ductile load" itself does not describe a force or stress on the pavement; it incorrectly implies a material property as a type of load.

Step 3: Identify the option that is NOT a type of force.
Environmental changes, drying shrinkage, and traffic load all represent distinct types of forces or stresses that act on cement concrete pavements. "Ductile load" does not describe a force but rather a characteristic (or lack thereof) of the material's response to stress. Concrete's behavior under load is typically brittle, not ductile. $$\boxed{\text{Ductile load}}$$