When did we start using tarmac on roads? Tarmac (asphalt) only really became popular once the motorcar was invented. Once you know that, it seems obvious, but it never really occurred to me.
We have had roads for thousands of years longer than we have had tarmac. The first roads were created when people started living together in settlements, which was probably about 10,000 years ago. The first roads were just tracks worn down by people walking them. About 7,000 years ago, the wheel was invented and people realized that they needed more reliable roads to pull the heavy loads they used the wheel for. That lead to the invention of paved roads in Mesopotamia in about 4,000 BC.
Many countries built roads and simple road networks, but it was really the Romans who pushed road building technology to the next level. The Roman legion was famous for how quickly and how far it could march in a day. This was down to their reliable roads. They dug a trench and filled it with layers of different sized rocks and topped it with shaped stones that were curved so that the rain would roll to the sides of the road. Some of their roads have lasted for over two thousand years.
By the Middle Ages, all roads were either made of stone (like Roman roads) or were dirt. The main problem was that carts traveled more easily on stoned, flat roads, but horses travel more easily on dirt roads that are softer on their feet and easier to grip. As most things were transported by horse, dirt roads were the most common.
“Macadam” was invented by John Loudon McAdam, a Scottish engineer, in 1820. The industrial revolution had meant that an increasing number of horse drawn vehicles were using the roads and people were becoming frustrated by the lack of road management. McAdam used a base of large stones with crushed stones bound with gravel on top. The road was then compacted to make it firm. He called this type of road surface “Macadam”. The roads were straight, flat, relatively simple to make, and easy to use, but they were holed easily and built up a lot of dust. Despite that, Macadam roads were popular because they were effective and economical. McAdam never used tar to hold his road surfaces down. He left the the stones on top open, and they were compacted down by the traffic, forming a harder layer.
In 1834, John Henry Cassell realized you could make Macadam roads firmer by using coal tar under the layer of crushed stones and gravel. He called his invention “pitch macadam”. In 1901, Edgar Purnell Hooley realized that you could mix the tar and the stones before spreading them on the road and then compact them with a steamroller to make the roads even firmer. He discovered this by accident when he visited an ironworks for business. He noticed the road leading up to the ironworks was perfectly smooth and when he asked people what had happened, he was told a barrel of tar had fallen off a wagon and burst open. Someone had poured waste slag, which is the waste from the iron smelting, on the road and it had solidified. Hooley realized that this road had far less dust on it than any of the other roads.
Hooley patented the word “tarmac”. Tarmac (asphalt) roads were few and far between at that point. As I said, horses found it easier to walk on dirt tracks, and horses were still the main form of transport.
However, by 1910, two things happened that caused a massive jump in the amount of tarmacked road surfaces. The newly invented motorcar became cheaper and more popular, and petroleum was discovered. Petroleum tar (bitumen) is far easier to make than coal tar and became available in large quantities. The number of cars was increasing so rapidly that the macadam roads couldn’t be repaired fast enough and the dust was a real problem. The governments of the world saw the benefits of tarmacadam and started tarmacadaming their roads as fast as they could.
These days, there are approximately 65 million km of roads in the world and the majority of it is tarmacked. All of this black road surface is a huge contributor to climate change, but what are the alternatives? Even if we invent different types of cars, we will still need road surfaces. I’m interested to see what the future brings.
So, tarmac, as we know it today, was invented in 1903 by accident, but it didn’t really take off until the increasing number of cars made it necessary. And this is what I learned today.
Sources
https://en.wikipedia.org/wiki/Tarmacadam
https://www.fhwa.dot.gov/infrastructure/back0506.cfm
https://en.wikipedia.org/wiki/Macadam
https://www.bbc.co.uk/nottingham/content/articles/2009/07/03/edgar_hooley_tarmac_feature.shtml
https://www.uksurfacings.com/news/tarmac-invented/
https://en.wikipedia.org/wiki/Road
https://en.wikipedia.org/wiki/Roman_roads
https://www.roadandtrack.com/car-culture/a4447/the-road-ahead-road-evolution/
http://www.laoistarmacadam.ie/asphalt-tarmacadam.html