Tarmac

Tarmac is the generic name given to road surfacing materials, which is comprised of tar-like materials mixed with mineral aggregates like Portland cement, sand, gravel or concrete. However, the word 'tar' is used to describe a number of distinct substances that aren't actually tar. Tar is refined natural resin or 'pitch', usually from the wood and roots of pine trees, but these are rarely found in our pavements. In fact, most of the 'tar' in tarmac is bitumen, which can be found in nature as a semi-solid form of petrol; but it is more commonly a bi-product of crude oil production by distillation. Popular lore holds that tarmac was invented by the Scotsman John McAdam, but in fact a county surveyor called Edgar Hooley was the man whose serendipitous encounter with an industrial spillage made road surfaces stick. McAdam had invented crushed stone surfaces, which were fine for horse-drawn coaches, but when cars became popular these surfaces were inadequate. 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 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.

For more information see our other sample of tarmac (220) and a blog post about this sticky substance.