Like any profession, pavement engineering comes with its terminology and, if you’re working in this area, you must understand it. In this article, Rob Graham takes you through some of the terms used by pavement engineers that you should know and understand.
What is pavement engineering?
First of all, let’s understand what is a pavement engineer, and what do they do? Pavement engineering is a branch of civil engineering, it involves knowledge of soils, hydraulics and other materials, and how these materials react to load or weight. A pavement engineer may design any man-made surface on natural ground that people can cross including: roads, car-parks, driveways and garden paths, as well as the pavements at the side of the road. They take into consideration the pavement function, loading demands, local geography and budget and use this knowledge to design a pavement buildup and surface layer that will stand up to real world demands.
So when you’re talking pavement engineering to a pavement engineer, it’s best to know exactly what they mean. Here are the top terms that you need to know.
The A to Z of pavement engineering – 44 pavement engineering terms you need to know
Asphalt: 1 A street paving material made of bitumen and mineral aggregate (such as sand or stone dust). The material makes up the large majority of all urban paved surfaces. 2 The black, viscous form of petroleum, found in natural deposits or made by refining, used in making the paving material. Commonly known as Tarmac or blacktop.
Asphalt chip sealing: Rolling a layer of aggregate into a base of asphalt emulsion binder to improve tyre grip and road wear, or alter the appearance or reflectivity. Using light-coloured aggregate can increase reflectance and reduce warming, or a local stone can help the road fit in better with its surroundings.
Bedding course / layer: A layer of relatively fine material (usually sharp sand) laid over the sub-base and providing a compressible bed for paving. This allows the paving to be placed over whatever lies beneath, a sub-base, a sub-grade or even something like a pre-existing concrete base.
Belgian block: A cubical paving block; a sett.
Bitmac: The road surface. From bitumen and Macadam.
Bitumen: Bitumen, sometimes called ‘tar’ or ‘pitch’ and is a petroleum-based hydrocarbon, the majority of bitumen used is obtained from crude oil and forms as a residue after the distillation process. Bitumen is used as a binder and combined with aggregates to create the top wearing road surface.
Block (concrete): A paving unit manufactured from precast concrete. The overall length divided by its thickness is less than or equal to four. This tends to create small stubby units which are very good at taking regular trafficking. Typical sizes for block paving are 200mm x 100mm x 80mm.
Bound (rigid) construction: Rigid construction, generally utilising concrete and cement mortars.
California Bearing Ratio (CBR): This is a measure of the strength of the subgrade of a road or other paved area and the materials used in its construction.
Causeway: A raised road or path across water or low-lying land, sometimes including flood arches.
Cobble: A naturally rounded stone (usually from rivers, fields or the sea) used for paving and walls. Setts are often popularly called cobbles (see cobbled).
Cobbled (of a street): 1 Paved with cobbles. 2 Paved with setts. When people refer to ‘cobbled streets’ they often mean streets paved with setts.
Cube: A square sett.
Dense Bituminous Macadam (DBM): A binder course used for roads with a large number of heavy commercial vehicles.
Dropped kerb: A short stretch of kerb that has been lowered to allow vehicles to drive across the pavement and park in driveways. It can also mean a section of kerb lowered to let people in wheelchairs or with buggies to cross the road.
Dropper kerb: The kerbstones required to create a dropped kerb.
Flagstone also flag (concrete): Paving units manufactured from precast concrete. Maximum length 1m and the length divided by thickness is greater than four. They tend to have a larger surface area and are more suited to pedestrian areas or lightly trafficked areas. A concrete paving unit becomes a flag once it exceeds the definitions of a block.
Granolithic paving: A material composed of cement and aggregate, used for paving.
Joints: Purposefully placed discontinuities in rigid construction that help to release stresses due to temperature variation, subgrade moisture variation, shrinkage of concrete etc.
Kerb: The edge of a pavement, often marked by a kerbstone (curbstone); a line of kerbstones where footway and carriageway meet.
Laying pattern / bond pattern: The arrangement of blocks or paving. Laying patterns include herringbone, stretcher and basket.
Ledger: A flat stone slab, usually inscribed.
Macadam: 1 (also stone macadam) A type of road construction with a smooth, hard surface, in which layers of compacted, crushed stone are bound with stone dust. It was pioneered by the engineer and road-builder John McAdam (1756–1836). 2 (also bitumen macadam) A similar type of road construction but with the addition of tar as a binder. See also bitmac and Tarmac.
Metalled road: One surfaced in road metal, in a late eighteenth century sense of the word metal, referring to the crushed rock that formed part of the system of building a sealed and waterproof road surface pioneered by the engineer John McAdam.
Pavement: 1. The raised surface for pedestrians beside a street or road. The US equivalent is generally sidewalk. 2 The structure of a road, including its surface and underlying foundations. 3 A paved surface. 4 An alley. From the Latin pavire, to beat hard.
Paver: 1 A paving stone or other paving block. 2 A person who lays paving.
Pebble: 1 A small stone, rounded by the action of water, ice or sand, as used in pebble paving. 2 (obsolete) A stone.
Pebble paving: Paving consisting of pebbles set in cement or some other binder.
Permeable paving: This is paving which is made of either a porous material that enables rainwater to flow through it or nonporous blocks which are spaced so that water can flow between the gaps.
Pitched: 1 (of a roof) Set on a slope. 2 A characteristic of paving that is composed of cobbles that are set on edge to provide an even surface.
Pitching: n. A pavement, particularly one made from stones set on end or edge; a foundation of a road or pavement made from such stones.
Road Base (also base and base course): This is a commonly used term to describe the upper-most layer of gravel/crushed rock in a road pavement.
Sand Joints: Material that is placed between stone pavers. Jointing sand prevents rain and moisture from penetrating the cracks between pavers and causing the soil underneath from washing away causing a shift in position of the paving.
Scoria block: A particularly durable and robust block, used for building and paving, made (from the eighteenth century onwards) from scoria (the residue of metal-smelting processes).
Sett: Paving units formed using natural stone through cutting or splitting. The length must not exceed twice the width and the width must not exceed twice the thickness. These are smaller element paving units similar to the concrete block.
Typical sizes of stone setts are 200mm x 100mm x 100mm or 300mm x 150mm x 150mm.
Slab: Paving units formed from natural stone, through cutting or splitting. The width of the stone must exceed two times the thickness. Similar in nature to concrete flags, however there is no upper limit on the length.
Typically used in bound construction and can take moderate trafficking.
Stable-block paver: A durable paving brick indented with a grid of lines to shed liquid and provide good grip.
Standard Axle: The axle load of a wheeled vehicle is the total weight bearing on the roadway for all wheels connected to a given axle and is used as a measurement to the structural strength of a pavement.
Sub-base: Sub-base is the layer of aggregate material laid on the subgrade, on which the base course layer is located. A sub-base is essential for surfaces used by vehicles, but it can be omitted when the pavement is only for pedestrians.
Sub-grade (grade): The ground you are constructing on.
Tarmac: 1 A generic name for asphalt surfaces. 2 A patented type of road-surfacing material composed mainly of compacted tar and aggregate. The word is a shortening of tarmacadam, a word combining tar- with the name of the engineer and road-builder John McAdam (1756–1836), who invented a process for building roads with a smooth, hard surface (macadam).
Unbound (flexible) construction: flexible construction, usually without concrete and cement mortars.
Wood-block paving: Wooden blocks (usually treated with bitumen or creosote) used for paving streets as a cheaper and quieter (though less durable) alternative to stone and asphalt.
We hope our glossary of pavement engineering terms is helpful. You can find out more about pavement engineering at www.marshalls.co.uk/DesignTeam.