Adhesion agent – A substance added to a bituminous binder to improve adhesion between the binder and aggregate. The term is usually applied to adhesion in the presence of water. Also commonly known as an anti-stripping agent.
Age hardening – Hardening of a bituminous binder due to loss of volatiles and oxidation of the binder resulting from exposure to weather over a period of time.
Aggregate – A material usually produced by crushing rock, slag, gravel, sand or similar material and screened to provide a specific size distribution.
Air voids – The spaces within the bulk of a material, such as an asphalt mix, which is not occupied by solid matter or filled with bituminous binder.
Application rate (aggregate) – The amount of aggregate spread in a sprayed seal expressed as square metres per cubic metre (m2/m3). Commonly known as the aggregate spread rate or coverage.
Application rate (binder) – The amount of bituminous binder applied in a sprayed seal expressed as litres per square metre (L/m2), usually expressed at 15°C. Commonly known as the spray rate.
Asphalt – A mixture of bituminous binder and aggregate, with or without mineral filler. Usually produced hot in a mixing plant and delivered, spread and compacted while hot. Also known as hot mix or hot mix asphalt (HMA).
Asphalt Institute (AI) – An association of international petroleum bitumen producers, manufacturers, and affiliated businesses, based in the USA.
Asphalt, dense-graded (DGA) – An asphalt comprised of coarse and fine aggregates, filler and a bituminous binder, which is placed hot and then compacted to a dense state as a road pavement layer. The aggregate gradation of dense graded asphalt is considered to be continuous and the intimate interlocking of the aggregate particles is a major factor in the strength of the compacted asphalt. Also known as asphaltic concrete.
Asphalt, hot rolled (HRA) – An asphalt material used as a dense wearing course, base course or road base material and which consists of a mixture of gap-graded coarse aggregate, fine aggregates, filler and bituminous binder. Common in the UK.
Asphalt, lake – A highly viscous natural bitumen found in well-defined surface deposits e.g. Trinidad Lake Asphalt.
Asphalt, open-graded (OGA) – An asphalt comprised of a large proportion of a single size aggregate, filler and bituminous binder, which has an interconnecting voids content of about 20% to 25%. Also known as porous asphalt and drainage asphalt.
Asphalt, stone mastic (SMA) – An asphalt with a high coarse aggregate content and a high volume of both filler and bituminous binder, the strength of which is predominantly provided by stone-on-stone contact of the coarse aggregate particles. Also known as Splitt Mastic Asphalt.
Asphaltic cement – North American term for bitumen.
Binder – A material that is used to hold aggregate particles together or to a substrate, such as bitumen in asphalt and sprayed seals, or cement in concrete.
Bitumen – A viscous liquid or solid, consisting essentially of hydrocarbons and their derivatives, which is substantially soluble in organic solvents, such as toluene and carbon disulphide, and is substantially non-volatile and softens gradually when heated. It is black or brown in color and possesses waterproofing and adhesive properties. It is either obtained by refinery processes from petroleum or is found as a natural deposit or as a component of naturally occurring asphalt, in which it is associated with mineral matter. Also known as asphalt in North America.
Bituminous – A material that resembles or contains bitumen.
Cold mix – A mixture of bituminous binder and aggregate, with or without added filler, which is produced warm or cold in a mixing plant and can be delivered in a workable condition suitable for stockpiling, spreading and compaction. It is typically used in areas where it is impractical to do repair work using hot mix.
Distillation, atmospheric – A refinery process that separates components in a crude petroleum oil by virtue of their different boiling points. Atmospheric distillation is carried out at normal atmospheric pressure.
Distillation, vacuum – A refinery process that separates components in a crude petroleum oil by virtue of their different boiling points. Vacuum distillation is carried out at reduced pressure to separate higher boiling components that would otherwise decompose if higher distillation temperatures and normal atmospheric pressures were used. Vacuum distillation is usually carried out on the residue obtained from atmospheric distillation.
Ductility – The characteristic of a bituminous binder that allows it to be elongated without rupture when stretched. Ductility values are defined as the distance to which a standard-sized sample of bituminous binder can be elongated before the thread so formed breaks under standard specified test conditions.
Ductility recovery – A modification of the ductility test whereby the sample is stretched to a thread of fixed length and then cut in the middle. The distance between the ends of the half threads, which develops after a standard period of time, is used to calculate the elastic recovery. It is usually expressed as a percentage of the elongation length.
Durability – The maintenance of performance properties of bitumen and bituminous materials to traffic, weather and other external factors. For bitumen, the measurement under standard specified test conditions of the long term effect of heat and air is known as the Durability and is based on the accelerated aging of bitumen to determine the time required for it to reach a specified viscosity level that has been associated with distress in pavement surfacings.
Dynamic viscosity – The ratio of shear stress to shear (strain) rate of a fluid.
Ethylene vinyl acetate (EVA) – A plastomeric polymer used in the modification of bitumen.
Flash point – The lowest temperature at which the vapour of a material momentarily catches fire when a flame is applied, but does not continue to burn.
Kinematic viscosity – The ratio of dynamic viscosity to density of a material.
Multigrade bitumen – A bitumen produced in a special refinery process to modify the temperature susceptibility otherwise characteristic of normal bitumen. A multigrade bitumen will exhibit a higher viscosity at a high service temperature and a lower viscosity at a low service temperature than an equivalent normal paving grade bitumen.
Penetration – An indication of the softness of a bituminous binder and measured as the vertical distance penetrated by a standard needle entering a bituminous binder sample under specified conditions of load, time and temperature.
Penetration index (PI) – The penetration index represents a quantitative measure of the temperature susceptibility of bitumen and is determined by calculation from two penetration values determined at different temperatures. Alternative equations exist that calculate PI from a combination of penetration, softening point and viscosity measurements.
Polyethylene (PE) – A plastomeric polymer used in the modification of bitumen.
Primer binder – A material which is more viscous than a primer that is used to act both as a primer and binder and used in primer sealing.
Rolling thin film oven test (RTFOT) – A laboratory test to simulate the ageing a bituminous binder will undergo in an asphalt mixing plant.
Softening point – The temperature at which a bituminous binder softens under standard specified conditions. Usually determined by the ring and ball softening point test, which measures the temperature at which a disc of the binder softens sufficiently to allow a standard steel ball, initially placed on the surface, to fall through the disc for a prescribed distance.
Tar – A viscous solid, semi-solid, or liquid material, black in colour and having adhesive properties, which is typically obtained by the destructive distillation of coal, wood or shale.
Temperature susceptibility – The change in viscosity of a bituminous binder with change in temperature. A high temperature susceptibility indicates a large change in viscosity with temperature.
Vacuum residue (vacres) – The residue obtained in the vacuum distillation of atmospheric residue.
Viscoelasticity – The rheological characteristic of a bituminous binder represented by both viscous and elastic behaviour, i.e. behaviour which is like that of both a solid and a liquid, in response to an applied stress.
Viscosity – The property of a fluid whereby, through internal friction, it resists movement and expressed as the stress divided by the strain rate.