Asphalt

A cost effective, highly durable and weather-sealed surface used almost exclusively in engineering projects, aggregate asphalt is renowned for its grip, extremely hard-wearing nature and heavy load-bearing qualities. A derivative of Tarmacadam, an innovation of the compacted stone Macadam surfaces invented in the 1820s by Scottish engineer John McAdam to provide a smooth, easy to construct paving surface, Welsh engineer Edgar Hooley added tar to seal the roads when laying, to prevent wear and dust. As motor cars became more common, it was imperative to provide a surface which could simultaneously withstand sustained, heavy use while remaining smooth to prevent puncturing tyres. With the growth in use of oil, bitumen, a naturally occurring byeproduct of oil, replaced tar to seal the surface. Combining layers of compacted mineral aggregate particles with the bitumen binds and waterproofs the surface, binding together more solidly over time. Higher quality grades of aggregate typically translate to longer lasting surfaces with less road noise than cheaper, poorer surfaces, while increasing grip, breaking efficiency and safety for foot and vehicular traffic and reducing tyre wear. Asphalt can also be easily recycled, redeployed in new paving and roads. This particular aggregate asphalt has a coarse, somewhat worn finish with gaps between the aggregate chips. The rough, riven texture is suggestive of a ‘chip seal’ surface; a cheaper variant of asphalt laid, compacted and coated with bitumen to provide a weatherproofing seal. The less grippy use of bitumen is offset by the coarse grain of the asphalt surface, which will provide grip although may have an oily sheen when wet due to the higher than normal bitumen content. The aggregate is laid randomly, compacted and bound with a gunmetal grey bituminous layer, commonly found on pavements and vehicular routes.