Inside Asphalt

You usually see asphalt from above as you are driving on it – it is the surface material on paved roads and highways. But here is a cross section of asphalt so you can see what it looks like inside.

Asphalt is a mixture of high-quality aggregate (approximately 94%) and asphalt cement (approximately 6%). In the cross-section picture, the lighter-coloured parts are aggregate and the darker material is the cement which contains tar.

Not all rock can be used for asphalt. Aggregate used in asphalt must be very high-quality - hard enough, strong enough, and durable enough – to build safe, long-lasting infrastructure.

After rock aggregate is extracted, a crusher like the one pictured below breaks it down and sorts it into various specific sizes (i.e. 19.5 mm stone, 9.5 mm stone, etc.) and Manufactured Sand (fines produced by crushing). When hot-mix asphalt is compacted, these irregularly shaped stones lock into place to give the pavement strength and rigidity.

An asphalt mix design is prepared based on the physical properties (hardness, absorption, dust content, etc.) of the aggregate source. The mix design specifies the ratio of different sized rocks to be combined and mixed in an asphalt plant. Other aggregate components may include sand and Reclaimed Asphalt Pavement (torn up asphalt that can be recycled and re-introduced into the asphalt mix).

Hot mix asphalt is transported from the asphalt plant, placed with specially designed equipment, rolled, and compacted to build infrastructure like roads, highways, runways, parking lots, driveways and recreational surfaces.

Aggregate is generally quarried in the communities where it is used to reduce trucking costs and environmental impacts associated with fuel consumption. Your local quarries are essential to making your community’s roads safe.

Aggregate is the most-mined material in the world because it is used in virtually all infrastructure. Nova Scotia needs about 10-15 million tons of aggregate each year to build and maintain its infrastructure.