Materials Up Close & Personal: TARMAC
16 April 2020
Maybe you can see the road from your window, or have been pacing the local pavements recently during your daily constitutional? If so, you might have noticed this sometimes sticky, sometimes oily, sometimes crumbly, black hash-brown of a material underfoot?
Tarmac is the generic name given to a huge variety of road surfacing materials that are generally made of bitumen, a tar-like material made from crude oil, mixed with aggregates like gravel, Portland cement, concrete, sand, and even rubber from old car tyres. The invention of this ubiquitous, silvery-black crust is thought to have been a happy accident, born out of a chance encounter with an industrial spillage.
Before the invention of tarmac the streets of London were paved with a variety of materials, including blocks of granite and creosote-soaked sections of Australian hardwood that - although quieter than stone - became oily, smelly and slippery when wet. Popular lore holds that tarmac was invented by the Scotsman John McAdam, but in fact it was a county surveyor called Edgar Hooley that made road surfaces stick. McAdam had invented crushed stone road surfaces, which were fine for horse-drawn coaches, but when cars became popular these surfaces were inadequate, as they threw up lots of dust, and potholes were easily formed. The story goes that Hooley was surveying in Derby and saw a smooth section of road near an ironworks. When he investigated, he was told a barrel of tar (the natural resin from pine trees) had fallen on the road, and waste slag from the furnaces had been poured on it to clear up the mess...and so tarmac was born!
Although some historians are unconvinced by the story of Hooley’s eureka moment, the material and manufacturing system that he patented in 1903 certainly produced a much smoother, stronger and less dusty surface than McAdam’s ‘unmetalled’ gravel road. Alongside the invention of pneumatic bicycle and car tyres, this allowed for much faster and less bumpy travel and so became our go-to for pavements, playgrounds and motorways.
About our new blog series 'Materials: Up Close & Personal'
We are excited to announce a new series of Materials Library profiles. Over the next few months our Materials Librarian Sarah Wilkes will be paying homage to those silent and humble materials that we surround ourselves with daily, but that often we don’t even notice. Every week or so, she will be exploring the expansive inner lives and backstories of the surfaces, substances and stuff around us, and sharing it with our community through our blog and social media #MaterialsLibraryUpCloseAndPersonal.
We would love you to join in too! Send us a picture of one of your favourite household substances with a few words about what you’ve noticed after spending some time getting to know your material cohabitants. A collection of these little gems will go up on our website soon.