Why Bitumen for Highways? – Key Material Properties Bituminous binders are extensively used in highway construction primarily because of which pair of material properties?

Introduction / Context:
Bituminous materials act as binders in asphalt mixes, holding mineral aggregates together while sealing the pavement against water ingress. Their viscoelastic behavior also provides flexibility and fatigue resistance under traffic loads and temperature cycles, making them the default choice for flexible pavements worldwide.

Given Data / Assumptions:

• Binder: bitumen or asphalt cement.
• Application: road surfacing and base/binder courses with aggregates.
• Design objective: durable, water-resistant, and well-bonded composite.

Concept / Approach:

The two most characteristic advantages of bitumen are its strong adhesion to mineral aggregates (binding) and its inherent impermeability (waterproofing). Together, these reduce raveling, stripping, and moisture damage. While mechanical strengths are relevant, it is the binder’s adhesion and sealing capacity that distinguish bituminous pavements from unbound granular layers.

Step-by-Step Solution:

Verification / Alternative check:

Moisture susceptibility tests (e.g., tensile strength ratio) and film thickness studies show that effective asphalt films mitigate stripping and improve durability, supporting the role of binding and waterproofing as primary benefits.

Why Other Options Are Wrong:

• Tensile/compression or shear/tensile alone: Oversimplify mechanical behavior and ignore the crucial sealing role.
• Bond and tensile: “Bond” overlaps with binding, but coupling with tensile alone neglects waterproofing, a principal reason for performance.

Common Pitfalls:

Confusing binder properties with the composite asphalt concrete properties; ignoring temperature susceptibility and need for proper gradation and air voids control.

Final Answer:

Binding and waterproofing properties