Bituminous materials in highway construction Why are bituminous binders (such as bitumen and asphalt) used primarily in road pavements and surfacings?

Introduction:
Flexible pavements rely on a binder to hold aggregate particles together and to protect the structure from water infiltration. Bituminous materials have long been preferred because their chemical and rheological properties suit these roles across a wide temperature range and traffic spectrum.

Given Data / Assumptions:

• Typical dense-graded asphalt concrete or surface dressing in highways.
• Properly selected penetration/viscosity grade binder and mineral aggregates.
• Design addresses traffic, climate, and drainage.

Concept / Approach:

The primary functions of a bituminous binder are to cement the aggregate skeleton (providing cohesion and adhesion) and to waterproof the pavement by limiting water ingress into underlying layers. These properties reduce stripping, raveling, and moisture damage and improve durability. While aggregates bear most of the structural loads, the bitumen provides the glue and moisture barrier critical for performance.

Step-by-Step Solution:

Verification / Alternative check:

Moisture susceptibility tests (e.g., tensile strength ratio) and binder–aggregate affinity studies show improved performance when adhesion and water resistance are optimized, confirming the central role of cementing and waterproofing.

Why Other Options Are Wrong:

Load bearing capacity (B) is mainly provided by the aggregate skeleton; specific gravity (C) is irrelevant to the primary function; black colour (D) does not facilitate markings—white/yellow thermoplastic paints provide markings; UV resistance only (E) is far from the primary reason.

Common Pitfalls:

Over-asphalting mixes causing bleeding; neglecting anti-stripping agents where aggregates are hydrophilic; ignoring drainage leading to water damage despite binder presence.

Final Answer:

cementing and water-proofing properties