Page 39 - Lecture Notes DCC3113

Road Aggregate

Natural Artificial

Igneus Sedimentary Metamorphic

Basalt Flint Hornfels
Gabbro Gritstone Quartzite Blast furnace
Granite Limestone Schist Slag
Porphry Gravel Burnt Shale
Sand

Figure 3-5: Classification of road aggregates

Figure 3-6: i. Rounded, ii. Irregular, iii. Angular, iv. Flaky, v. Elongated, vi. Flaky & Elongated
(Source: BSI 812: 1975)

Aggregate physical properties

Aggregates can be classified by their mineral, chemical and physical properties. The pavement industry
typically relies on physical properties for performance characterization. An aggregate’s physical
properties are direct result of its mineral and chemical properties.

Important properties of aggregates are:
i. Strength – to withstand crushing, impact during construction and traffic load
ii. Soundness – resistance to disintegration under weathering
iii. Shape and surface texture – help in interlocking, resistance to sliding, affect strength
iv. Affinity – properly coated by binder
v. Relative density and absorption – stripping, drying time and mix design
vi. Resistance to wear (hardness) – polished under traffic, skid resistance
vii. Gradation – quality and pavement strength

34