ATT Flat, Elongated Particles & Sand Equivalent Flashcards

The particle index test (ASTM D3398) measures aggregate quality based on:

Answer: Particle shape and surface texture using void content

ASTM D3398 determines the particle index by measuring the voids content at two compaction levels, reflecting aggregate shape and surface texture.

Which aggregate shape characteristic generally produces the highest concrete strength at a given water-cement ratio?

Answer: Angular, rough-textured particles

Angular, rough-textured aggregates develop stronger mechanical interlock and bond with cement paste, producing higher concrete strength.

Crushed aggregate typically has a higher particle index than natural gravel because:

Answer: Its angular shape and rough texture create more voids in a loose state

The angular, fractured faces and rough surface texture of crushed aggregate result in higher void contents and thus a higher particle index compared to rounded natural gravel.

In aggregate quality evaluation, a fractured face count is most relevant for:

Answer: Coarse aggregate used in asphalt mixtures

Fractured face counts are commonly specified for coarse aggregate in hot-mix asphalt to ensure adequate shear resistance and resistance to rutting.

Which test best evaluates the presence of plastic fines (clay minerals) in fine aggregate that could reduce concrete durability?

Answer: Sand equivalent test (ASTM D2419)

The sand equivalent test (ASTM D2419) is specifically designed to measure the relative proportion of clay-like plastic fines in fine aggregate.

When evaluating coarse aggregate shape for Portland cement concrete, the most significant concern with using highly elongated particles is:

Answer: They are prone to breaking during mixing and reduce the aggregate's effective size

Highly elongated particles are fragile and tend to fracture during concrete mixing, reducing the effective aggregate size and potentially degrading concrete performance.