what is tarmac

Tarmac, also known as tarmacadam, is a road surfacing material made by combining crushed stone, sand, and tar. It was patented by Welsh inventor Edgar Purnell Hooley in 1902 and is a more durable and dust-free enhancement of simple compacted stone macadam surfaces invented by Scottish engineer John Loudon McAdam in the early 19th century. The terms "tarmacadam" and tarmac are also used for a variety of other materials, including tar-grouted macadam, bituminous surface treatments, and modern asphalt concrete. Tarmac is strong, water-resistant, and enables a good grip as well as giving a good aesthetic to the finished surface, which is why it is most commonly used on tarmac driveways. The tar used for tarmacadam is a natural black liquid substance that can be extracted from the ground where it is found in large tar pits or obtained as a by-product of coke production from the distillation of coal. Tarmac is often used interchangeably with asphalt, but they are not the same material. Asphalt is a mixture of aggregates and bitumen that needs up to two days before it completely cures, whereas tarmac is a combination of crushed stone and tar that cures quickly. In addition to road surfacing, the term "tarmac" is also used to refer to the paved runway at an airport where airplanes taxi, pull up to a gate, or head out to the runway.