AGGREGATES - Materials for Civil and Construction Engineers - page 194

SUMMARY

Aggregates are widely used as a base material for foundations and as an in-
gredient in portland cement concrete and asphalt concrete. While the geo-
logical classification of aggregates gives insight into the properties of the
material, the suitability of a specific source of aggregates for a particular ap-
plication requires testing and evaluation. The most significant attributes of
aggregates include the gradation, specific gravity, shape and texture, and
soundness. When used in concrete, the compatibility of the aggregate and
the binder must be evaluated.

QUESTIONS AND

PROBLEMS

5.1 What are the three mineralogical or geological classifications of

rocks and how are they formed?

5.2 Discuss five different desirable characteristics of aggregate used in

portland cement concrete.

5.3 Discuss five different desirable characteristics of aggregate used in

asphalt concrete.

5.4 The shape and surface texture of aggregate particles are important

for both portland cement concrete and hot mix asphalt.
a. For preparing PCC, would you prefer round and smooth aggregate
or rough and angular aggregate? Briefly explain why (no more
than two lines).
b. For preparing HMA, would you prefer round and smooth aggre-
gate or rough and angular aggregate? Briefly explain why (no more
than two lines).

5.5 A sample of fine aggregate has the following properties:

Wet mass = 521.0 g

Dry mass = 491.6 g

Absorption = 2.5%

Determine: (a) total moisture content, and (b) free moisture content

5.6 Use the following information to determine the total and free mois-

ture contents in percent:

Mass of wet sand = 627.3 g

Mass of dry sand = 590.1 g

Absorption = 1.5%