There are three pavement types:
- Flexible – Asphalt concrete
- Rigid – Portland cement concrete
- Interlocking pavers – Stone, brick, or blocks
But there are seemingly infinite variations of each.
The black stuff is asphalt concrete (left photo), also called hot-mix asphalt concrete. In some states or regions, it is called bituminous concrete, or in New England, Macadam. You may see asphalt concrete abbreviated AC, HMA, or HMAC. The black color comes from the asphalt cement which is the thickest portion or residue after refining petroleum oil. Heat is used to mix and hold the ingredients together. An AC pavement can be a hot as 325 degrees when it is laid down. We call it a flexible pavement because the pavement layers bend slightly under a vehicle tire.
The P in Portland cement concrete is capitalized because modern concrete was improved using the limestone of Portland, England. Concrete is typically abbreviated PCC. Where AC mixture is created by a thermo/heating process, PC concrete mixture is created by a chemical reaction between the Portland cement and water. This slurry of cement, rock, and water reacts and hardens, binding the slurry and aggregate together, called curing. The result is a rigid pavement because it has only microscopic bending under vehicle tires. PCC curing creates heat and stress in the pavement layer which will crack to relieve the stress. To control the cracking the PCC pavement is typically cut into slabs, roughly 12 by 12 feet.
Interlocking pavers are stone, brick, or concrete blocks. They are set into a sand bed over a base that can be aggregate, asphalt concrete or Portland cement concrete. Installation can be labor intensive, so paver applications are typically used for accents for architectural features or stormwater drainage.
Photographs by Zimmer Consultants