The Aggregates & Recycling Information Network

Glossary: P

  • Paid-up Capital

    The proportion of the issued capital which has been paid for by shareholders.

  • Palaeontology

    The study of fossils.

  • Palaeozoic

    The era in time ranging from 590 to 213 million years ago. It comprises the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian systems.

  • Pan mixer
    Pan Mixer

    A mixer comprising a horizontal circular pan and a blade.  Either the pan or the blade may rotate to create the mixing action and the mixture is discharged through doors in the base of the pan.  Commonly used to mix ready-mixed concrete.

  • Parallel Pinch

    Term applied to gyratory crushers designed in such a way that the displacement of the head is the same from top to bottom, resulting in the full crushing stroke being applied to large pieces of rock immediately they enter the crushing chamber.

  • Particle Velocity

    A measure of ground vibration. Describes the velocity, in metres per second, at which a particle of ground vibrates when excited by a seismic wave.

  • Parting

    A very thin bed of rock in a coal seam.

  • Pascal

    Unit of pressure equal to 1 newton/m2.

    Symbol: Pa

  • Patching

    The execution of small local repairs in a road surfacing.

  • Pavement

    The part of the road structure above the sub-grade.

  • Payload

    The rated payload of a dumptruck is the maximum load as specified by the manufacturer.

  • PC

    abbr. personal computer

  • Peak Value

    The highest instantaneous value of a periodic quantity taken over one cycle.

  • Pegging

    The obstruction of a screen surface by single fragments which become wedged in the apertures.

  • Pegmatite

    A coarse-grained, quartz-feldspar igneous rock of variable colour and very variable physical properties.

  • Percentage Open Area

    The ratio of the total area of the apertures to the total area of the wire cloth, perforated plate or wedge-wire screening panel.

  • Percussive Drilling

    A method of drilling whereby repeated blows are applied by the bit, which is repositioned by intermittent rotation.

  • Percussive-rotary Drilling

    Rotary drilling combined with a percussive action on the bit.

  • Period

    The duration of one cycle.

    Symbol: T

    Units: seconds

  • Perlite

    A variety of obsidian consisting of the oxides of silicon and aluminium combined as a natural glass. When crushed and heated, it expands to form a lightweight aggregate.

  • Permeability
    1. The rate of diffusion of a fluid under pressure through a porous material.
    2. The ratio of flux density produced in a material to that which would be produced in space by the same magnetizing force.
  • Permian

    The final period of the Palaeozoic era between 286 and 248 million years ago, and the corresponding system of rocks.

  • Personal Protective Clothing

    Special clothing worn for personal protection, such as boots, helmets, goggles, ear-defenders etc.

    abbr. PPE 

  • PETN

    abbr. pentaerythritol tetranitrate

    This forms the core of a detonating fuse.

  • Petrology

    The study of the origin, chemical and mineral composition, structure and alteration of rocks.

  • PH

    abbr. the potency of hydrogen

    The pH scale represents the degree of acidity and alkalinity on a scale of 0 to 14; 0 is strongly acidic, 7 neutral and 14 strongly alkaline.

  • Phase Voltage

    The voltage between any line of a three-phase electrical system and the neutral point of the system.

  • Phasor

    A straight line drawn to represent an alternating current or voltage in both magnitude and direction.

  • Photogrammetry

    The making of maps by photography from the air using reference points of known level and position which can be identified on the photographs.

  • Phyllite

    A dark-grey or greenish metamorphic rock, coarser-grained and less perfectly cleaved than slate, but smaller grained and better cleaved than schist.

  • Piano Wire

    High-tensile steel wires. Such wires may be stretched to a predetermined tension over a frame to form the screening medium for effective screening of damp, sticky, fine material.

  • Picking station
    Picking Station

    Picking stations are used when manual sorting of the feedstock is required. Manual sorting may be required when unwanted materials cannot be reliably or efficiently removed by other methods. Picking stations are horizontal conveyor belts configured to allow operatives to remove unwanted items. This configuration includes the consideration of correct ergonomics, efficiency and safety.

  • Pilot Plant

    A small-scale treatment plant in which representative tonnages of mineral can be treated under conditions which foreshadow those of the proposed full-scale operation.

  • Pinion

    The smaller of a pair of high-ratio bevel gear wheels.

  • Pipe Conveyor

    A belt system in which the belt is formed into a pipe shape, enclosing the material and allowing the conveyor to negotiate steep gradients and horizontal curves.

  • Pipe-ventilated

    Term applied to an electric machine which is totally enclosed except for inlet and outlet pipes through which clean ventilating air passes to the machine.

  • Piston Pump

    Piston pumps, as used in hydraulic systems, create a flow by pistons moving in and out of cylinder bores as the latter pass over inlet and outlet ports. The stroke is imparted to the pistons either by having the cylinder barrel set at an angle to the drive shaft or by means of a swashplate mounted on the drive shaft.

  • Pitch
    1. The angular inclination, measured in relation to the direction of the strike, of the axis of any feature in a known plane.
    2. The residue, which is liquid when hot and solid when cold, obtained by the distillation of tars.
  • Pitching

    Large stones used for road-base or revetment, usually between 178mm and 305mm in depth, placed by hand with small stones or other material in the interstices and compacted by rolling or other means.

  • Pitman

    An old term for a rod which connects a rotary with a reciprocating object, such as the eccentric shaft with the toggle plates of a jaw crusher.

  • Pitot Tube

    A tube of specific dimensions inserted parallel to the flow of the fluid. The tube has two orifices, one facing the flow and hence receiving total pressure and the other static pressure at one side. The pressure difference can be used as a measure of flow rate.

  • Pitting

    Wear consisting of small pits in the surface, believed to be due to fatigue failure of metal in the region of maximum shear stress, normally at a small depth below the surface; a common type of failure in the rolling elements of bearings.

  • Plagioclase

    Silicates of aluminium with calcium and sodium, a member of the feldspar family; an important constituent of many plutonic and volcanic rocks.

  • Plain Bearings

    Bearings in which the load-bearing surfaces slide relative to each other.

  • Plain Carbon Steels

    Steels which contain 0.1% to 0.7% carbon, with no other, deliberately introduced alloying elements. The properties of these steels vary with the carbon content and they are divided into four divisions: low-carbon steels contain up to 0.15% C; mild-carbon steels; 15% to 0.29% C; medium-carbon steels 0.30% to 0.59% C; and high-carbon steels 0.60% to 1.70% C.

  • Plain Detonator

    A detonator for use with safety fuse.

  • Plane-tabling

    A quick method of mapping areas of open country using a plane table and alidade.

  • Planetary Gear

    Any gear-wheel whose axis describes a circular path round that of another wheel, as in a differential gear.

  • Planimeter

    An instrument used to obtain accurate direct readings of areas on plans.

  • Plaster Shooting

    A form of secondary blasting in which explosive is detonated in contact with the rock without the use of a shothole.

    See also: mudcap

  • Plastic Cracking

    Cracks which form in concrete while it is still in the plastic state and, depending on weather conditions, in about the first 6h after the concrete has been placed.

  • Plasticizer

    A water-reducing admixture which, when added to fresh concrete, increases its workability and, by reducing the amount of free water, increase its strength.

  • Plate Feeder

    A device consisting of a hopper the reciprocating base of which moves the rock forward on each stroke.

  • Plate press
    Plate Press

    A development of the plate-and-frame filter press in which the filtration cavity is created by two adjacent corrugated, recessed plates.  In both cases, the plates are covered with filter cloth and the slurry is pumped into the cavity under very high pressure.  Water passes through the cloth and the cavity fills with the suspended solids, the filter cake.  The cake is discharged by separating the plates.

  • Plate Tectonics

    The concepts which ascribe vulcanicity and crustal weakness to the interaction of moving lithosphere plates.

  • Plc


    1. public limited company.
    2. programmable logic controller.
  • Pleistocene

    The earliest epoch of the Quaternary Period during which the Ice Age occurred. It covers the period between 2 million and 10 thousand years ago.

  • Plough Plate

    A device fitted to a belt conveyor installation for the purpose of removing material from the top of the belt and spillage and fines from the return belt before it reaches the return drum.

  • Plug And Feather

    A technique for splitting stone, by which split wedges (feathers) are hammered into a line of holes and pressure exerted on the stone by inserting chisels (plugs) into the feathers.

  • Plummer Block

    A journal bearing consisting of a box-form casting holding the roller bearing or bearing brasses.

  • Plutonic

    A term applied to a group of deep-seated, coarse-grained igneous rocks which solidified at great depth, eg granites.

  • Pneumatic

    Operated by air pressure.

  • Pneumoconiosis

    An occupational disease occurring in mines, quarries and other workplaces where some types of dust are prevalent. It is fibrosis of the lungs caused by asbestos, silica and other types of dust.

  • Pole
    1. The part of a magnet from or to which the lines of magnetic flux diverge or converge.
    2. A terminal of an electricity supply.
  • Polished Stone Value

    A relative measure of the extent to which different types of roadstone in the wearing surface will polish under traffic as determined by the method defined in BS EN 1097 Part 8.

    abbr. PSV

  • Polyurethane

    Range of resins, both thermoplastic and thermosetting, used in the lining of pipes, vessels and other parts subject to wear, and in the manufacture of screen panels.

  • Porosity

    The ratio of the volume of voids to the total volume of the rock or the soil sample.

  • Porphyry

    An igneous rock which contains large feldspar crystals (phenocrysts) in a fine-grained groundmass.

  • Portland Cement

    Cement made by burning together, in a kiln, a mixture of limestone and clay to form a clinker rich in calcium silicates. This is ground to a fine powder with a small proportion of gypsum which regulates the rate of setting when cement is mixed with water. Calcining occurs at temperatures in excess of 750°C and clinkering at +1,450°C. There are several types of Portland cement including: ordinary, rapid-hardening, sulphate-resisting and white.

  • Post-tensioning

    A method of pre-stressing concrete by tensioning steel tendons passing through ducts after the concrete has hardened.

  • Potash Mica


    See: muscovite

  • Potential Energy

    Energy due to the position of a body.

  • Pour Point

    The lowest temperature at which a petroleum-based oil will flow. Used as a guide to the suitability of a lubricant for low temperature operation.

  • Powder Factor

    The mass of explosive (kg) used to break each cubic metre of rock. It offers a comparative guide to blasting performance.

  • Power

    Energy transferred in a certain time interval, ie the rate of doing work. The basic unit is the watt (W) which is defined as a rate of working equal to one joule or one newton-metre per second.

  • Power Factor

    Ratio of the total power (watts) dissipated to the apparent power (volt-amperes) in an ac system. Power factor = WI VA.

  • Power Take-off

    An external splined shaft on a tractor used, while the tractor is in motion or stationary, for driving ancillary plant.

  • Power-assisted Steering

    A system in which the driver is assisted in the steering of the vehicle by, for instance, a hydraulic ram, powered by a hydraulic pump driven by the engine, fitted to the steering drag-link.

  • Power-factor Correction

    The use of capacitors or synchronous motors to restore a lagging power factor to near unity.

  • Pozzolana, Pozzolanic

    Originally a volcanic earth from Pozzuoli (Italy), rich in alumina, silica and iron, which, when added to lime mortar, reacted to produce an hydraulic set. Now applied to other materials such as crushed brick or pulverised fuel ash.

  • Pozzolanic Material

    A naturally occurring or artificial material which has in itself little or no cementing property but which will combine with lime in the presence of water at ordinary temperature to form a stable insoluble compound having cementing properties.

  • PPE

    abbr. personal protective equipment

  • PPV

    abbr. peak particle velocity

    A measure of ground vibration. Describes the velocity, in metres per second, at which a particle of ground vibrates when excited by a seismic wave.

  • Pre-Cambrian

    The period of time (about 4,000 million years) from the consolidation of the Earth’s crust to the beginning of the Palaeozoic era, and the corresponding system of rocks.

  • Pre-splitting

    A blasting technique in which charges of low concentration are used in closely spaced holes of significantly greater diameter than the diameter of the charge, to create in a solid mass of rocks a plane of weakness which will determine the limit of breakage from subsequent blasts or subsequent detonations in the same blast.

    Also: controlled blasting or cushion blasting

  • Pre-tensioning

    A method of prestressing concrete by tensioning wires around which the concrete is placed and compacted. On hardening, the temporary anchorages are released and the stress is taken up by the bond between the wires and the concrete.

  • Precast Concrete

    Concrete beams, columns, lintels etc which are manufactured and partly matured on site or in a factory before use.

  • Precoated Chippings

    Aggregate chippings which have been coated thinly with bituminous material for scattering over a wearing course or for use as a surface dressing. Where bitumen is added just sufficiently to present a prepared surface for added bitumen, the term ‘lightly coated chippings’ is used. 

    Also: coated chippings

  • Preference Shareholders

    Shareholders having a right to a certain fixed dividend before any distribution of the remainder of the profits to the ordinary shareholders. These shareholders do not usually have voting rights.

  • Preformed Rope

    A steel-wire rope in which the strands are bent before they are twisted together, making the rope less likely to spin.

  • Prescreeners

    Prescreeners (also known as grizzly screens) are large strong screens often located at the start of a screening or crushing operation. They can be used in two ways, to protect the machinery, such as crushers or conveyors being presented with oversized materials, and/or to remove undersized material before crushing.

  • Pressure

    Force per unit area.

    Units: pascal (Pa) = 1N/m2 (1bar = 100,000 Pa)

  • Prestressed Concrete

    Reinforced concrete which is pre-compressed, using high-tensile wires, which enable it to withstand tensile stresses when loaded and cracking is reduced or eliminated.

  • Preventive Maintenance

    Inspections of plant and machinery at regular intervals with the condition of each item recorded. This system should reduce downtime by providing warnings of the need for overhauls and by parts replacement at predetermined intervals before breakdown.

  • Price-earnings Ratio

    The relationship between profits and the publicly quoted value of a company’s shares, expressed as market value/earnings per share.

    abbr. PE

  • Pricker

    A non-ferrous tool for making a hole in the primer cartridge to receive the detonator.

  • Primary Blast

    The breaking out of stone from its natural state by means of explosives.

  • Primary Crushing

    The crushing of run-of-quarry stone from pieces of up to 1.5m across to rocks of up to 300-400mm.

  • Primary Saw

    Large circular saw, frame saw or wire saw for primary sawing of blocks into slabs of the thickness required.

  • Primary Winding

    The winding of a transformer which is connected to the source of energy.

  • Prime-mover

    Internal combustion engine, steam engine, steam turbine, water turbine etc which converts fuel or natural energy into mechanical power.

  • Primer

    A boosting charge placed in contact with a detonator or detonating fuse to ensure detonation of the main charge.

  • Primer Cartridge

    The explosive cartridge into which the detonator has been inserted.

  • Priming

    Filling a pump with water before starting.

  • Principle Of Moments

    For equilibrium the sum of the clockwise moments about a point must equal the sum of anti-clockwise moments about that point.

  • Prismatic Compass

    A pocket compass, used by geologists and surveyors, from which bearings can be read by holding it to the eye and looking through the prism at the compass card while sighting the target.

  • Probability

    In statistics, the number of chances by which an event may happen compared with the total number of chances; applied in designing some types of screen.

  • Probability Screening

    [img_assist|nid=11995|title=|desc=|link=none|align=right|width=139|height=172]A method of screening which by making extended use of the probability of a particle passing through an aperture, allows sizing at fine sizes to be performed with relatively large apertures.

  • Process Chart

    A diagrammatic means of recording the sequence of activities in an existing method under study, using five standard symbols.

  • Profit

    Revenue less costs.

  • Profit And Loss Account

    An account which, by law, all registered companies must keep, and each calendar year publish, for the shareholders’ information. It must give a true and fair view of the profit and loss of the company for the related financial year and be presented in one of four approved formats.

  • Prospect

    An area of land which shows sufficient promise of mineral wealth to warrant exploration.

  • Prospecting

    The search for indications of workable mineral deposits, usually on the surface.

  • Protective Equipment

    Devices such as circuit breakers, earthleakage protection, overload protection etc which protect electrical equipment and its operators in the event of faults and overloads.

  • PSV

    abbr. polished stone value

    A relative measure of the extent to which different types of roadstone in the wearing surface will polish under traffic as determined by the method defined in BS EN 1097 Part 8.

  • Pudding Stone

    Conglomerate of pebbles, naturally cemented with silica or calcite.

  • Pull-push Loading

    A system of loading in which twin-engined motor scrapers are operated in pairs, assisting in loading each other in turn. Scrapers used in this way are generally of the same type and require to be fitted with special connections.

  • Pulp

    A suspension of fine mineral particles in water, ie a slurry.

  • Pulverized Fuel Ash

    Residue from the high-temperature burning of pulverized coal in power stations; it is an impalpable dust which may have pozzolanic properties.

    abbr. PFA

  • Pumice Stone

    A lava froth containing minute gas cavities, used as a cleansing and polishing material and as an aggregate in lightweight concrete.

  • Pusher Loading

    Loading of motorized scrapers with assistance from a pusher bulldozer. The bulldozer usually provides this assistance to a team of, say, three scrapers.


    abbr. Provision and Use of Work Equipment Regulations

  • PVC

    abbr. polyvinyl chloride

    Most widely used vinyl plastic in the manufacture of pipework, cable covering etc.

  • Pyroclastic

    Descriptive of rock formed of fragments of igneous rock, ejected by volcanoes, embedded in finer material such as ash or tuff.

  • Pyroxene

    Group of rock-forming silicate minerals characterised by a chain silicate structure.