Tarmac is one of the most widely used road surfacing materials in the world. Also known as tarmacadam, it makes up over 90% of paved roads across the UK and Europe. But what exactly is tarmac made of?
Whether you’re paving a major highway, resurfacing your driveway, or just curious about what’s under your feet, read on to learn all about what gives tarmac its unique properties.
A Brief History of Tarmac: From Coal Tar to Asphalt
The term “tarmac” originated in the early 20th century from “tarmacadam”, which was invented by Welsh scientist Edgar Purnell Hooley in 1901. Hooley experimented with adding tar – a thick, black liquid extracted from coal or wood – to the crushed rock material used in macadam road construction, invented by Scotsman John Loudon McAdam in the 1820s.
By coating the crushed stone with tar, Hooley created an improved paving material that was less dusty and more durable than standard macadam. After receiving a patent in 1901, the first tarmacadam road was laid in Nottingham in 1902.
Key Takeaway: The original tarmac formula combined crushed stone aggregate with coal tar as a binder, creating a stronger and smoother road surface than previous materials.
Initially, natural tar deposits were the main source of tar for tarmacadam production. However, as oil refining advanced in the early 1900s, petroleum-derived bitumen became more available as a byproduct.
Since around the 1950s, bitumen has largely replaced coal tar as the key binding agent in tarmac and most modern asphalt mixes. The terms tarmac and asphalt are often used interchangeably today, although traditional tarmacadam used tar instead of bitumen.
Over the past century, tarmac and asphalt technology has continued advancing. Different aggregates like sand and gravel are combined with modifiers to create specialized mixes for various paving applications.
The Key Ingredients: A Look at What Modern Tarmac Contains
So what exactly goes into tarmac? While mixes can vary, the two essential components of tarmac are aggregate and bitumen.
Aggregate: The Crushed Stone Base Material
Aggregate makes up around 95% of a typical tarmac mix. It provides the base structure and strength. Aggregates used include:
- Crushed stone – Usually limestone or granite. Different sizes of crushed stone are blended based on the mix design.
- Gravel – Rounded, water-worn stone fragments. Provides more workability than crushed stone.
- Sand – Very fine aggregate that fills the gaps between larger pieces.
- Mineral filler – Rock dust that helps fill air voids.
Bitumen: The Viscous Petroleum Binder
Bitumen is the key binding agent used in modern tarmac. It makes up around 5% of the mix but plays a crucial role in holding the aggregates together.
Bitumen is:
- A byproduct of petroleum refining, obtained through fractional distillation.
- A black, highly viscous liquid or semi-solid hydrocarbon mixture.
- Waterproof and weather/chemical resistant.
- Provides flexibility and adhesion between aggregate particles.
Bitumen grade and chemistry can be modified to optimize properties like stiffness, aging resistance and workability based on climate and traffic volumes. Polymer-modified bitumen is also common.
Step-by-Step: How Modern Tarmac is Produced
We’ve covered the key ingredients, so how is tarmac actually made? Here is an overview of the modern tarmac production process:
1. Extract and Process Aggregates
Aggregates like crushed limestone are mined from quarries using excavators or blasting. They are then washed, sorted by size, and stored. Further crushing and screening may be required to achieve the desired gradation.
2. Produce and Modify Bitumen
Bitumen is obtained as a residue from petroleum refining. The chemistry can be optimized by:
- Air blowing – Oxidizing the bitumen to increase viscosity.
- Adding polymers – Improves elasticity, cohesion and heat resistance.
3. Combine and Heat Materials
Aggregates and bitumen are combined in a mixing plant. The materials are heated to allow proper coating and workability during paving.
Mixing temperature varies:
- Hot mix asphalt: ~150-180°C
- Warm mix asphalt: ~100-140°C
- Half-warm mix asphalt: ~70-100°C
4. Lay and Compact Tarmac
The hot tarmac mix is hauled to the paving site in dump trucks or luges. Paving machines evenly spread and level the material. Compaction rolls are then used to compress it into a dense, smooth mat.
Tarmac vs. Asphalt vs. Concrete: How Do They Compare?
Tarmac, asphalt, and concrete are the most common choices for paving roads, driveways, and parking lots. How do they stack up?
Tarmac and asphalt are closely related – both combine aggregates with a bituminous binder. The main differences are:
- Traditional tarmac uses coal tar, while modern “tarmac” uses bitumen, making it essentially asphalt.
- Asphalt has a wider range of mix designs and modifiers.
Tarmac/asphalt and concrete have more noticeable differences:
| Tarmac/Asphalt | Concrete | |
|---|---|---|
| Ingredients | Aggregates + bitumen binder | Cement + aggregates + water |
| Structure | Flexible | Rigid |
| Durability | Good, but can fatigue/rut over time | Excellent, lasts longer under heavy loads |
| Cost | Lower material and construction cost | $2-5 more per sqft |
| Maintenance | Periodic resurfacing | Minimal long-term maintenance |
| Noise | Quieter surface | Noisier surface |
Asphalt and tarmac are preferable for lower-traffic pavements because of their lower cost and easier installation/repair. Concrete excels under heavy traffic loads and extreme climates but needs stronger foundations.
Eco-Friendly Tarmac: Developments in Sustainability
While traditional hot mix tarmac/asphalt has major environmental impacts, modern options are much more eco-friendly:
- Warm mix asphalt reduces production temperatures, cutting energy use and emissions.
- Half-warm mix asphalt uses less heat still, with additives to improve workability.
- Recycled asphalt reuses old pavement, decreasing the need for virgin materials.
- Permeable tarmac allows rainwater drainage, avoiding flooding and pollution.
Sustainable pavement standards like LEED now incentivize greener practices for tarmac driveways and roads. With over 90% recyclability and advanced mixing processes, tarmac can be an environmentally sound material.
Uses of Tarmac: From Road Surfaces to Tennis Courts
Thanks to its smooth finish, durability, and water resistance, tarmac is used in a wide variety of paving applications:
- Roads and highways – Tarmac handles heavy loads and weather, making it ideal for major roads.
- Driveways and car parks – Provides an affordable, low-noise surface for homes and businesses.
- Airports – Strength and skid resistance make tarmac perfect for runways and taxiways.
- Paths and walkways – Offers a smooth, wheelchair-friendly surface.
- Tennis courts – Provides the consistent bounce needed for sport.
- Play areas – Cushioned tarmac helps prevent injuries from falls.
From residential driveways to commercial highways, tarmac offers an accessible paving solution. Modified mixes like porous tarmac also expand its possibilities.
FAQs About Tarmac Composition, Production and Uses
What is the difference between tarmac and asphalt?
Traditional tarmac uses coal tar as the binder, while modern tarmac and asphalt both use petroleum-derived bitumen. So while “tarmac” is still used colloquially, nearly all tarmac today is technically a form of asphalt.
Why is tarmac used for roads instead of concrete?
Tarmac is generally cheaper, faster to install, and easier to repair than concrete roads. It also provides a smoother, quieter ride for vehicles. Concrete excels in heavy-traffic areas but requires higher upfront costs.
How long does tarmac last compared to other road surfaces?
Properly maintained asphalt/tarmac roads typically last 10-25 years. Concrete may last 25-50 years but needs stronger foundations. Gravel roads require frequent grading and last 5-10 years.
Can tarmac be recycled?
Yes, old asphalt pavement can be milled up and reprocessed into new asphalt at rates over 90% recyclability. This reused asphalt reduces the need for virgin paving materials.
Is tarmac better than concrete for driveways?
For most residential driveways, tarmac is preferable to concrete. It’s smoother, cheaper, and easier to repair. Concrete offers greater durability for high-traffic driveways. Porous tarmac also handles water better.
Conclusion
From its tar-and-stone origins to state-of-the-art asphalt mixes, tarmac has come a long way in the past century while remaining a ubiquitous paving material.
Understanding the components that give tarmac its unique properties provides insight into why it became so popular. While traditional coal tar tarmac is now obsolete, modern bitumen-based tarmac/asphalt offers an advanced, eco-friendly solution for everything from highways to tennis courts thanks to innovations in production and recycling.
Tarmac offers an unrivaled combination of affordability, durability, and practicality that will likely keep it on top as a paving material for many years to come. And by leveraging green technologies like warm mix asphalt, it still has room to improve.
So the next time you pull into a smoothly paved driveway, park on a new tarmac lot, or walk down an airport taxiway, you’ll know exactly what gives this ubiquitous surfacing material its staying power.