The Aggregates & Recycling Information Network

Glossary: R

  • R&D

    abbr. research and development.

  • Racking Course

    A compacted layer of graded stone spread over a pitched foundation to fill interstices and bring it to the correct profile before surfacing.

  • Racking-in

    The use of a second addition of chippings in a road dressing, usually of a smaller size, rolled in to interlock the surface.

  • Radian

    The angle subtended at the centre of a circle by an arc equal in length to the radius; two p radians correspond to 360°.

  • Radio-controlled

    The actuation and especially remote control of a device without the need for a cable (hard-wired) connection.  

    Also: wireless

  • Rag Bolt

    A foundation bolt of increasing size towards its end and having jagged points on its surface to prevent its withdrawal when cast or grouted into the concrete.

  • Ragging

    The layer of dense material placed above the screen in jigging.

  • Raise

    A vertical or steeply inclined shaft which has been driven upwards.

  • Raise-boring

    The process of excavating a rock pass or a ventilation shaft between the surface and a lower level or between two levels by means of a drill erected at the upper level. A relatively small diameter hole is drilled between the two levels, the bit is removed, replaced by a large-diameter reaming bit and the hole reamed to the required diameter in an upward direction.

  • Ranging Rod

    A straight rod 2m long used by a surveyor to set out points in a straight line.

  • Rating

    The whole of the rated values and operating conditions of electrical machines and equipment. The rating of a motor may be stated as being the output power of the motor under specified working conditions, eg cooling air temperature less than 40°C, without the temperature rise exceeding a specified value.

    Also: motor rating 

  • Ratio Analysis

    The use, by management and investors, of ratios of profitability in assessing the financial performance of a company; other ratios may be used to indicate its financial status.

  • RAWP

    abbr. regional aggregates working party.

  • Reactance

    The rms voltage/current ratio in a circuit having inductance or capacitance or a combination of the two.

    Symbol: X

    Units: ohms

  • Reactive Component

    The component of the phasor current or voltage which is in quadrature with the voltage or current.

    Also: idle component and wattless component

  • Reactive Power

    The product of the reactive component of the current and the voltage or the reactive component of the voltage and the current.

    Unit: volt-ampere reactive (VAr)

  • Reagent

    A chemical used to produce a desired reaction.

    See also: flotation reagent

  • Ream

    To increase the diameter of a borehole using a reaming bit or reamer.

  • Reaming Bit

    A rotary bit used to enlarge the diameter of a borehole.

  • Reaming Shell

    A cutting cylinder, fitted between the bit and the core barrel or casing, used to maintain the diameter of a borehole.

  • Rebound Hammer Test

    The Schmidt hammer is used to give a quick approximate value of concrete strength after it has been calibrated by tests made on cubes and units made from the same concrete.

  • Receiver

    A storage vessel for compressed air. It receives air from the compressor, smoothing out fluctuations in demand and allows moisture and oil carried in the air to collect and be drained off.

  • Recent

    The current epoch in the Earth’s history, comprising the 10,000 years or so since the end of the last glaciation.

    Also: Holocene

  • Rectification

    The process of obtaining uni-directional currents and voltages from alternating currents and voltages.

  • Rectifier

    A device for converting an alternating current into a direct current by the inversion or suppression of alternate waves.

  • Recycled Concrete Aggregate

    A designation used in BS 8500 for recycled aggregate principally comprising crushed concrete.

    abbr. RCA

  • Reduced Level

    The level of a point in relation to a prescribed datum.

  • Reduction Ratio

    In general, the ratio of the size of the feed to the size of the product in a crushing operation.

    Note: There are several methods of expressing the ratio, eg limiting reduction ratio, 80% reduction ratio, mean reduction ratio.

  • Refraction

    Change of direction of a wave when it travels from one medium to another.

  • Regression Curve

    The line which accurately represents a series of experimental or test results plotted on a graph and which has been obtained by mathematical analysis of those results.

  • Regulating

    Forming a surface to a required shape or contour.

  • Regulating Course

    A course of variable thickness applied to a road surface to adjust the shape preparatory to resurfacing.

  • Regulators

    A type of flotation reagent which may be divided into two groups.

    Also: depressants

  • Rehabilitation

    The reinstatement of an excavated site to an acceptable form of after-use.

  • Reinforced Concrete

    Concrete in which steel bars or wires are embedded to provide increased strength; the steel takes the tensile forces and the concrete the compressive forces.

  • Reinforcement

    Round or deformed steel bars or welded steel mesh fabric embedded in concrete to strengthen it. These materials are covered by British Standards 4449, 4461, 4482 and 4483.

  • Relative Density

    The ratio of the density of the substance to the density of water. Relative density was formerly called specific gravity and has no units.

    Also: specific gravity 

  • Relay

    An electromagnetically operated switch employed to open or close an independent circuit.

  • Relief Valve

    A valve used in hydraulic systems which will open and pass oil when the pressure to which it has been set is exceeded.

  • Relieving Deck

    A screen plate with large apertures mounted over the screen deck in order to reduce the load on it.

  • Relieving Shot

    A shot fired to dislodge or expose a misfire.

  • Remote Sensing

    Techniques of data collection of the Earth’s surface from a distance eg by satellite.

  • Remould

    A used tyre which has had a new tread vulcanized to the undamaged casing.

  • Repose Angle

    The maximum angle between the surface of a heap of loosely piled material and the horizontal. 

    Also: angle of repose

  • Resistance

    The opposition offered by a conducting material to the passage of a current.

    Symbol: R

    Units: ohms

  • Resistivity Surveying

    An electrical method of geophysical prospecting which depends on variations in the conductivity, or resistivity, of rock layers. The apparent resistivity of the ground is determined by measuring the potential difference across two electrodes while introducing current into the ground through two other electrodes.

  • Resistor

    A component of an electrical circuit, the primary property of which is resistance.

  • Resonance Screen

    A screen with a period of oscillation at or very close to the natural period of oscillation of the mass of the screen on its resilient mounting.

  • Reticule

    The set of cross-hairs fitted into the diaphragm of a surveying instrument telescope. 

    Also: graticule

  • Retread

    A reconditioned tyre on which the tread has been renewed.

  • Revenue

    Income from any source.

  • Revetment

    A cladding of stone or concrete to protect a sloping embankment or shoreline.

  • Rhyolite

    Fine grained or glassy acid rock, usually volcanic.


    abbr. Reporting of Injuries, Diseases and Dangerous Occurrences Regulations

    Regulations that impose a legal obligation upon employers to report certain ‘incidents’ to the HSE.

  • Riffling

    Sample reduction using a riffle box. This is a box comprising a number of internal chutes directed alternately towards one of two trays. By this means the sample is halved and the material on one tray rejected.

  • Rig

    Commonly used to denote a mobile drilling machine.

  • Right Of Way

    A right enjoyed by either particular persons or the general public over land on foot or with animals or in a vehicle. The right may be subject to conditions and restrictions of use by the grantor or derived from uninterrupted custom.

  • Rigid Pavement

    Any pavement substantially constructed of high strength concrete.

  • Ring System

    An electricity distribution system in which the substations are connected in a continuous closed circuit from the main substation.

  • Rip-rap

    Rock in lump form used as bulk fill for stabilization or as protection against erosion.

  • Rippability

    Term applied to rocks which indicates whether or not they can be ripped. The factors on which it depends include: the characteristics of the rock, the power of the ripper, the type and number of shanks etc.

  • Ripper

    A bulldozer fitted with one or more hooked tines (pointed shanks) which can be forced into the ground hydraulically to break it up as the tractor moves forward.

  • Ripping

    The process of breaking ground with a ripper.

  • Rise And Fall

    A method of calculating reduced levels using the rise or fall from each staff location to the one following it.

  • Risk

    A measure of the probability that a hazard will cause harmful consequences, eg death, injury and damage.

  • Riven

    Surface produced by splitting along the cleavage planes.

  • RMS Value

    abbr. root-mean-square value

    This value of an alternating current or voltage is also known as the ‘effective value’ because it is measured in terms of the direct current or voltage that would produce the same heating effect if applied to the same resistance.

  • Road Breaker

    An electric, compressed air or hydraulic power driven tool for breaking up road pavements by impact.

  • Road Heater

    A self-propelled or towed machine for heating a road surface by causing flames, radiant heat or hot air to play upon it.

  • Road Tar

    Tar conforming to a specification (BS 76) defining its properties for use in road construction.

  • Roadbase

    An obsolete term for the one or more layers of material constituting the main structural element of a pavement now described as basecourse.

  • Rock

    A mass of mineral material, including organic material, either consolidated or not, but excluding soil.

  • Rock Joint

    Fracture or fissure in rock without displacement.

  • Rock Mechanics

    The study of rocks in situ including their strengths, stresses, strains, friction, elasticity etc, and the use of this information in assessing such things as the stability of rock slopes.

  • Rock Pile

    The broken rock resulting from a primary blast.

    See also: muckpile 

  • Rock Sill

    Near horizontal, sheet-like intrusion of igneous rock.

  • Rockhead

    The boundary between superficial deposits (drift) and the underlying solid rock.

  • Rod

    A bar the end of which is slotted, tapered or screwed for the attachment of a drill bit.

  • Rod Mill

    A horizontal rotating cylindrical mill containing steel rods and rock fragments.

  • Rolled Asphalt

    A dense mixture of gap-graded aggregate, filler and bitumen which can be used for wearing course or basecourse applications.

  • Roller Rock Bit

    A rotary bit fitted with two or more hardened steel or tungsten carbide-tipped rollers of cylindrical or conical form.

    Also: three-cone (tri-cone) bit 

  • Roller-bearing

    A shaft bearing consisting of inner and outer races between which are hard steel cylindrical rollers held in position by a cage. Bearings of similar construction to ball bearings with parallel, tapered or spherical steel rollers instead of steel balls. Suitable for heavier loads than ball bearings.

  • Rolling Element Bearings

    Bearings in which the load is carried by rolling members, ie balls or rollers.

  • Rolling Resistance

    The force opposing the motion of a wheel rolling on a surface caused by the distortion of the line contact due to the normal force between them.

  • Root-mean-square Value

    This value of an alternating current or voltage is also known as the ‘effective value’ because it is measured in terms of the direct current or voltage that would produce the same heating effect if applied to the same resistance.

    abbr. RMS value

  • Rope Drilling

    A system of percussive drilling in which the drill string is suspended at the end of a long rope.

  • Rope Shovel

    A face shovel excavator which has a bucket controlled by steel ropes. Once common in rock quarries and opencast coal sites, now often replaced by hydraulic excavators or wheeled loading shovels.


  • ROPS Cab

    A driver’s cab having roll-over protection. It is designed to give added protection to the driver in the event of the machine accidentally turning over while in operation and gives a more comfortable and quieter ride.

  • Rotor

    The rotating part of an ac machine.

  • Rougher Cells

    Flotation cells used to remove a rough concentrate at the first stage of treatment.

  • Round

    A number of shots intended to be fired either simultaneously or with delay periods between shots.

  • Royalty

    Payment by an operating company to a landowner or owner of mineral rights for tonnage of mineral extracted or sold.

  • RSJ

    abbr. rolled steel joist.

  • Run Of Mine/quarry

    The products of a mine/quarry before crushing, sorting and cleaning.

  • Run-off

    The quantity of water, from rain and snowfall, flowing from a catchment area past a given point in a stated period of time.