In highway maintenance, where is plastic bitumen most appropriately used? (Add practical context: choose the application that benefits from a flexible, gap-filling, and water-resisting bituminous mix blended with fillers.)

Introduction:
Plastic bitumen (often called bituminous mastic when loaded with mineral fillers) is designed to be workable at placement, then set into a dense, slightly deformable mass. The concept tested here is the correct field application where this mix's flexibility and adhesion are most valuable.

Given Data / Assumptions:

• Plastic bitumen is bitumen blended with fillers to improve stiffness, adhesion, and water resistance.
• It is placed in confined small volumes rather than as a continuous structural layer.
• Traffic loads demand a material that accommodates slight movements without raveling.

Concept / Approach:
Bituminous mastics excel at sealing voids and bridging small movements. They bond to the sides of cracks and reduce water ingress, protecting the sub-layers from moisture damage and preventing crack propagation under traffic.

Step-by-Step Solution:

Verification / Alternative check:
Maintenance manuals place bituminous mastics under crack treatment and localized patching rather than as primary surfacing. Field practice confirms longevity when cracks are cleaned, dried, primed (if specified), and filled flush.

Why Other Options Are Wrong:

• Road pavements (main wearing course): Needs dense/stone mastic or asphalt concrete with graded aggregates for stability.
• Expansion joints: Prefer polysulfide, silicone, or specialized elastomeric joint sealants with designed movement capacity.
• General waterproofing of basements: Uses membranes/coatings tailored for hydrostatic pressure; pavement mastics are not the design solution.

Common Pitfalls:
Confusing stone mastic asphalt (a wearing course) with bituminous mastic used for sealing; using plastic bitumen as a structural layer; neglecting crack cleaning and drying leads to poor bonding.

Final Answer:
Crack filling and patch repair in flexible pavements