Tarmacadam

Tarmacadam (pronounced tahr-muh-kad-uhm)

(1) A paving material consisting of coarse crushed stone covered with a mixture of tar and bitumen.

(2) To cover or surface with tarmacadam.

1880–1885: The construct was tar + macadam (the spelling tar-macadam was also used).  Tar was from the Middle English ter, terr & tarr, from the Old English teoru, from the Proto-West Germanic teru, from the Proto-Germanic terwą (related to the Saterland Frisian Taar, the West Frisian tarre & tar, the Dutch teer & German Teer), from the primitive Indo-European derwo- (related to the Welsh derw (oaks), the Lithuanian dervà (pinewood, resin), the Russian де́рево (dérevo) (tree) and the Bulgarian дърво́ (dǎrvó) (tree)), from dóru (tree).  Tar described the black, oily, sticky, viscous substance, consisting mainly of hydrocarbons derived from organic materials such as wood, peat, or coal and it has been in use for millennia including as a water-proofing agent in the warships of Antiquity where it worked well but, being flammable, increased the vessels vulnerability to attack by “fire-ships”, an early “high-tech” weapon.  It’s used also as a descriptor of the solid residual by-product of tobacco smoke, seen often in anti-smoking campaigns, often demonstrating the effect on the lungs.  The old slang of a “tar” (also “jack tar”) being a sailor was unrelated to the hydrocarbon derivative and was a clipping of “tarpaulin”, allusion to the clothing seafarers wore.  In drug user slang, “black tar” was a form of heroin.  Tarmacadam is a noun & verb, and tarmacadaming & tarmacadamed are verbs; the noun plural is tarmcadams.

A Clan MacAdam family crest (there are many MacAdam crests and coats of arms).

The origin of the prefixes “Mc” & “Mac” in Scottish surnames lie in the Gaelic language historically was spoken in Scotland and both “son of”, thus indicating lineage, specifically to signify “son of” a particular person or ancestor (a la Robinson, Johnson et al).  Over centuries, the original “Mac” prefix was sometimes shortened to “Mc” but both forms are used interchangeable, carrying the same meaning.  The prefixes were an example of Celtic naming traditions (obviously most prevalent in Scotland & Ireland but also in other Gaelic-speaking regions) where surnames often were patronymic, based on the name of a father or ancestor.  Family lineage and heritage are important aspects in the naming traditions and conventions in many cultures and the “Mac” & Mc” use was the Gaelic practice.  The surname McAdam (also as MacAdam, Macadam & Mac Adaim (Irish)) belonged to a Scottish Gaelic clan which originated as a branch of Clan Gregor and although it has spread to many nations of the old British Empire (notably Ireland, the US, New Zealand, Australia and Canada), it is most prominent in the Galloway and Ayrshire regions of Scotland.

Clan MacAdam tartans: Reproduction (left), Modern (centre) and Ancient (right).  There are many Clan MacAdam tartans and the provenance of some may be dubious.  

The Gaelic “son of Adam” existed in those cases where the Biblical name had not been Gaelicized.  In this sense it was a companion of McGaw & MacGaw (from a Gaelicized form of the personal name) which in Ireland evolved as McCadden (in County Armagh) and McCaw (in County Cavan).  The Gaelic original seems to have been MacAdaim, introduced into both England and Scotland by twelfth century crusaders returning from the various (and usually unsuccessful) expeditions to “free” the Holy Land from Islamic control; Among the warrior crusaders, it was a fashion to give their children biblical names and because of the patronymic convention, they became elements in surnames from the thirteenth century onwards, MacAdam & McAdam proliferating.  So, given the etymology, it would be reasonable to assume tarmacadam might be pronounced tahr-mick-adam but even by the turn of the twentieth century it had become a stand-alone English word pronounced tahr-muh-kad-uhm.  

Tarmacadaming in progress (the worker on the right wielding a “tarmac rake”).  Like an iceberg, much of what a road is lies beneath. 

John McAdam (1756- 1836) was a Scottish civil engineer who specialized in road-building who in 1824 invented a process he called “macadamisation”.  His innovation was a system which enabled roads to be built with a smooth hard surface, using a defined mix of materials consisting particle of mixed sizes and predetermined structure; it offered the advantage of a surface which was more durable and less muddy than soil-based tracks.  Except when subjected to sustained periods of extreme weather, a characteristic of a “macadamed” surface was that vehicular transport tended to “compact and preserve” the integrity of the structure rather than wear and contribute to its deterioration.  However, as early as 1834 others began experimenting with tar (essentially as a sealant or sort of glue) as a way of strengthening a macadam road, increasing its durability, some of these enchantments involving both a top and underlying layer of tar and others adding to the surface alone.  Tar-augmented macadam was in use by the late nineteenth century but it never became widespread until the demands imposed by increasingly fast and heavy motorized vehicles.  John McAdam personally was never an advocate of the use of tar in road-building, his concern that there existed a tendency for such methods to “trap” water which would expand in sub-zero temperatures, causing the surface to break up; for this reason he preferred a structure which “breathed”, allowing the slight slope he engineered into his projects to permit natural drainage.

PavingExpert.com has a fine page explaining the terminology.

It was the Welsh civil engineer Edgar Hooley who in 1901 “invented” tarmacadam although “discovered” is a better description of what happened because the circumstances were serendipitous.  Mr Hooley was walking towards an ironworks when he observed an unusually smooth stretch of road and when he enquired what had caused the phenomenon, he was told a large barrel of tar had fallen onto the road and smashed, disgorging the contents which quickly spread, making a black, stick, mess.  Staff from the ironworks had been dispatched with a cart of slag (a waste-product from the blast furnaces with instructions to spread it across the road and Mr Hooley noted the impromptu resurfacing had solidified the road, giving it a marvelously smooth, consistent surface with no rutting and no dust.

Prototype William C Oastler steamroller, Cooke Locomotive factory, Paterson, New Jersey, 1899.

Within months, Mr Hooley had completed his design for a process he called “tarmac”.  This involved mechanically mixing tar and aggregate into a dispensing device which “laid-it-down” to be compacted with a steam-engine powered roller (the appropriately named “steamroller”).  What made the process possible was the basic tar being modified with the addition of pitch, cement & resin.  In 1902, Mr Hooley was granted a patent and the essence of his design remains in use today.  It produced good results but it was a more expensive method than the traditional approach but what radically reduced the cost was the emergence in the US of a large-scale petroleum industry which produced large quantities of bitumen as a by-product, something for which there was then little demand.  The sudden availability of vast quantities of bitumen meant coal tar could be replaced and Mr Hooley’s mechanized process then became a cheaper method of road building, the combination of the dispensing device and steamroller eliminating much of the labor-intensive activities inherent in the business of macadamisation; the most familiar modern version of the process in the “tar and chip” method which civil engineers refer to as BST (bituminous surface treatment).

Tarmacadam variations.

The classic tarmac surface is now rarely used although in a curious linguistic quirk, the word persists as a common term describing the apron outside airport passenger terminals (the “marshalling area” where aircraft are parked to allow passengers to embark & disembark (de-plane the current buzz phrase)) although these are now typically constructed with concrete.  In some markets “asphalt concrete” (the smooth, black surface sometimes called “road carpet”) but the word “tarmacadam” remains commonly used in road-building and other fields in civil engineering.  Technically, Tarmacadam should now correctly be referred to as “bituminous macadam” (“Bitmac” in professional slang) and it’s one of those processes which is appropriate for some jobs and not others, largely because while a relatively cheap method when used at large scale, for small areas it can be very expensive because the machinery is all designed to be deployed at scale.

On the tarmac: Lindsay Lohan in costume for Liz & Dick (2012), Van Nuys Airport, Los Angeles, June 2012.  Based on this image, the Van Nuys tarmac is of concrete construction.