Bituminous road materials: In producing plastic bitumen (plasticized or mastic-type bitumen mixes), which of the following has historically been used as a fine filler to modify consistency and performance?

Introduction / Context:
Bituminous mixes often include mineral fillers to adjust viscosity, stiffness, and durability. In older formulations of plastic or mastic-type bitumen, a fine fibrous filler was sometimes employed to improve stability and workability for waterproofing and paving applications.

Given Data / Assumptions:

• Question refers to traditional practice (“plastic bitumen”) used in legacy specifications.
• We are selecting the typical fine filler cited in classical construction-materials references.

Concept / Approach:
Classical plastic/mastic bitumen mixes used asbestos powder as a filler to increase cohesiveness, reduce temperature susceptibility, and improve deformation resistance. While modern practice may avoid asbestos due to health hazards, many traditional questions reflect earlier materials technology where asbestos filler was common in mastics and plastic bitumen.

Step-by-Step Solution:

Verification / Alternative check:
Legacy textbooks and specifications mention asbestos-filled mastics for roofing and paving; contemporary standards now specify safer alternatives, but the exam context typically expects “asbestos powder.”

Why Other Options Are Wrong:

• Shale or talc powders: used in some fillers but not the standard association for plastic bitumen in older references.
• Plastic powder: not a conventional filler in bitumen mastics; modern “plastic roads” use waste plastics differently (as modifiers), not as fine mineral fillers.
• None of these: incorrect because asbestos powder is classically cited.

Common Pitfalls:

• Confusing modern modified bitumen technology with historical exam content.
• Assuming health restrictions retroactively change classical answers; exams often retain legacy terminology.

Final Answer:
asbestos powder