The modern paved surfaces seen on roads and driveways are composite materials engineered for durability and strength. While the public widely uses the term “tarmac” to describe the black pavement of roads and parking lots, this name is technically inaccurate for nearly all contemporary applications. The material is formally known as asphalt concrete, a precise blend of natural and manufactured ingredients. This exploration will detail the material’s specific components, the process of its creation, and clarify the distinction between “tarmac” and modern “asphalt.”
The Primary Ingredients
The pavement material used today is primarily composed of two main components: aggregate and a binder. Aggregate forms the structural skeleton of the mixture, making up roughly 90 to 95% of the total weight, and includes coarse aggregate (crushed stone and gravel) and fine aggregate (sand and mineral filler).
The angular shape and rough texture of the coarse aggregates carry traffic loads, distributing weight and preventing deformation through particle-to-particle interlocking. Fine aggregates, such as sand and mineral fillers like limestone dust, fill the voids between the larger stones. This blend provides the structural integrity, density, and resistance to wear that makes the surface long-lasting.
The second primary ingredient is the binder, a sticky, black, semi-solid substance called bitumen, also known as asphalt cement. Bitumen is a byproduct of crude oil distillation and acts as the “glue” that coats and holds the aggregate particles together. This petroleum-based binder provides the pavement with flexibility and waterproofing properties. The proportion and grade of the bitumen are carefully controlled, as they significantly influence the mixture’s performance and resistance to cracking and deformation.
Manufacturing and Laying the Surface
The process of creating modern pavement begins by heating and drying the aggregate materials in a central mixing facility, commonly called a hot mix plant. The most widespread method is Hot Mix Asphalt (HMA), where the aggregate and the bitumen binder are heated to high temperatures. This ensures the binder is liquefied and can fully coat every stone. Production temperatures for HMA typically range between 300°F and 350°F (150°C to 180°C), depending on the specific grade of bitumen used.
After mixing, the hot asphalt concrete is transported to the construction site in insulated trucks, maintaining a temperature high enough to remain workable. During paving, a specialized machine called a paver spreads the mixture evenly across the prepared road base. The temperature during this laying phase is kept between approximately 275°F and 350°F to allow for proper material flow and bonding.
The final step is compaction, achieved using heavy roller machines. Compaction must occur while the material is still hot to achieve the required density and strength, which determines the pavement’s long-term durability and resistance to traffic wear. Recently, Warm Mix Asphalt (WMA) technologies have been developed. WMA uses additives to reduce production and paving temperatures by 20 to 55°C (40 to 100°F), lowering energy consumption and improving workability.
Tarmac Versus Asphalt
The confusion between “tarmac” and “asphalt” is rooted in history, as the two terms refer to materials with a fundamental difference in their binder. The term “tarmac” is a shortened version of “Tarmacadam,” a proprietary road surface invented in the early 1900s. Original Tarmacadam used crushed stone bound together with refined coal tar as its binder.
Modern road surfacing, or Asphalt Concrete, uses bitumen—a petroleum-based product—as the binder instead of tar. Tar was largely phased out of construction due to its susceptibility to spills and association with carcinogenic properties. Although Tarmacadam is rarely used today, “tarmac” became a common generic term for any black, paved surface.