On the many roads crisscrossing the world, two terms have persistently sparked debates among engineers, motorists, and language enthusiasts alike: “asphalt” and “tarmac.” Often used interchangeably, these words seem to refer to the same thing – the surface we drive upon daily.
On the many roads crisscrossing the world, two terms have persistently sparked debates among engineers, motorists, and language enthusiasts alike: “asphalt” and “tarmac.” Often used interchangeably, these words seem to refer to the same thing – the surface we drive upon daily.
Yet, in road construction terminology, there is a nuanced difference between these materials that has far-reaching implications for road design, maintenance, and environmental impact. What are these differences exactly? This article explores the differing history, composition, and uses of these two common paving materials.
The Historical Origins
Asphalt traces its roots back to ancient civilizations, including the Mesopotamians and Egyptians, who used naturally occurring bitumen – a viscous, sticky, black substance – to waterproof their structures and pave roads. Over the centuries, various civilizations have employed asphalt for road construction, and the word itself is derived from the ancient Greek “asphalt,” which means “secure.”
On the other hand, tarmac owes its name to the British road builder Edgar Purnell Hooley, who patented the “Tarmac” process in 1902. Contrary to popular belief, “tarmac” is not an abbreviation but a proper noun derived from the company name, “Tar Macadam Syndicate Limited,” which Hooley founded. The process involved coating broken stone with tar, creating a solid surface that offered better durability and resistance to weathering.
Chemistry and Composition
The divergence between asphalt and tarmac lies in their chemical makeup. Asphalt is a composite material primarily derived from crude oil. Wet asphalt mixture consists of crushed stone, sand, and gravel aggregates mixed with bitumen- a by-product obtained from the heavy distillation of petroleum. The bitumen acts as the binding agent holding all other composites together.
On the other hand, tarmac involves a combination of tar and crushed stone. Unlike bitumen, tar can be derived from burning coal and petroleum, but it acts as a binding agent the same, holding the stone aggregates together. The tar coating provides a smooth and waterproof surface making the tarmac driveway an ideal choice for runways, racetracks, and other areas where water resistance is crucial.
Road Performance and Maintenance
Asphalt and tarmac differ in performance characteristics, lifespan, and maintenance needs. Asphalt’s flexibility and ability to accommodate temperature variations make it a resilient choice for roads in regions with extreme weather conditions, as it can withstand freeze-thaw cycles and is relatively easy to repair through patching and resurfacing.
In contrast, the tarmac’s rigidity makes it susceptible to cracking under extreme temperatures and heavy traffic loads. Furthermore, due to its highly waterproof nature, any water trapped beneath the tarmac can further damage it, as it lacks the drainage properties of asphalt. As such, tarmac maintenance often involves more frequent repairs, such as crack sealing and occasional resurfacing.
Environmental Implications
Unfortunately, asphalt and tarmac both impact the environment negatively. Asphalt’s main component, bitumen, is a crude oil by-product, and its extraction and production contribute significantly to global CO2 emissions. Similarly, tarmac’s reliance on tar involves extracting and processing coal and petroleum, which also exude copious quantities of greenhouse gases.
Nonetheless, both materials are recyclable to some extent. Asphalt reclaimed from damaged roads can be crushed and reused in new road construction, reducing the demand for new materials and mitigating environmental impact. Tarmac recycling, while feasible, is less common due to the complexities of separating the tar from the crushed stone.
Regional Preferences and Usage
While both asphalt and tarmac find widespread use in road construction, regional weather and practical considerations often dictate where and when they are used. For example, In the western hemisphere, asphalt dominates the road-building landscape due to its durability, flexibility, and ease of maintenance. However, tarmac remains the prevalent choice for airport runways and race tracks because of its waterproof nature and smooth finish.
Conclusion
The asphalt vs. tarmac debate has been ongoing for years. Tarmac has become synonymous with asphalt in everyday language in the U.K. and many European countries, further muddying the distinction between the two materials. Nevertheless, understanding the nuances between asphalt and tarmac sheds light on the complex world of road construction and the choices that shape our modern infrastructure.
