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Abbreviation for Autoclaved Aerated Concrete, a type of CELLULAR CONCRETE, with a density around 650 kg/m3 and a thermal conductivity of some 0.08 W/ m.K; usually available in the form of blocks or planks, possibly reinforced. Often laid with a thin adhesive bed in place of mortar. Can be cut with a saw; can be used for load-bearing walls (up to two storeys) and the planks also for floors and roofs.
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The ancient Greek calculating frame consisting of beads sliding on thin rods, still widely used in Asia. The name was given to the uppermost member of the classical column head, which is a plate of varying thickness, because of its similar appearance.
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The reduction of a health hazard to an acceptable level by encapsulation, removal or demolition.
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Experimental rule enunciated by D. A. Abrams in 1919: ‘With given concrete materials and conditions of tests, the quantity of mixing water determines the strength of concrete, as long as the mix is of workable plasticity.’ See figure.
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The wearing away of the surface of a material by the cutting action of solids. There are numerous abrasion resistance tests. Comparing similar materials by the same test gives satisfactory results; however, the correlation between different tests is difficult, and the method of testing must always be specified. Abrasion tests may be rolling or sliding in nature, with or without abrasive. Usually the test is run for a definite number of strokes with a definite pressure, and the loss of weight is measured.
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The capacity of a surface to resist deliberate ABRASION or ordinary wear.
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Acrylonitrile-butadienestyrene, a thermoplastic material of good chemical resistance.
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The x-axis, or horizontal axis, of a CARTESIAN COORDINATE system.
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Generally, the moisture content of air, in gram of water vapour per kg of dry air, although in specialist terms it would mean the mass of water per unit volume of the air/ vapour mixture (g/m3). See also HUMIDITY RATIO.
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Temperature measured from ABSOLUTE ZERO. When measured in CELSIUS (centigrade), it is called the Kelvin scale (K). Measured in FAHRENHEIT, it is called the Rankine scale, but this is rarely used.
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The magnitude of a quantity irrespective of whether its sign is positive or negative.
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The actual volume of the particles of sand, concrete aggregate, etc. It is determined by immersing the aggregate in water, and measuring the volume displaced.
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The lowest temperature which can be reached in theory, when the molecules of a perfect gas would possess no kinetic energy, and its volume would become zero. This occurs at –273.16°C (–459.67°F). The absolute temperature scale is measured from absolute zero. See KELVIN.
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A component of the solar flat plate collector that absorbs solar radiation and converts it into heat.
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In lighting, the ratio of the LUMINOUS FLUX absorbed by a body to the flux which it received. (b) In radiation, a surface property of bodies, either (i) the ratio of radiant heat absorbed by a surface to the incident irradiance, or (ii) the ratio of radiant heat absorbed by a surface to the heat that would be absorbed by a perfect absorber BLACK BODY (which, by definition, is numerically the same). It is wavelength-dependent, but can be used referring to a given broad range of wavelengths, (e.g. solar) or for a specified narrow band of wavelengths. It can be measured for a beam radiation of specified angle of incidence, or as a total hemispherical absorptance. (See also SELECTIVE SURFACE.)
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The process whereby liquid is drawn into the permeable pores of a porous solid. (b) Transformation of radiant energy to a different form of energy by the intervention of matter, as opposed to transmission which is the passage of radiation through matter without change of its frequency. (c) Absorption of sound. See SOUND ABSORPTION.
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See SOUND ABSORPTION COEFFICIENT
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A refrigeration cycle. It utilises two phenomena: (a) the absorption solution (absorbent plus refrigerant) can absorb refrigerant vapour; and (b) the refrigerant boils (flash cools itself) when subjected to a lower pressure. These two phenomena are used to obtain refrigeration. In the lithium bromide absorption machine, the bromide is used as an absorbent, and the water as a refrigerant. See also COMPRESSION CYCLE.
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A hollow excavation (maintained with perforated walls and a top covering, or by filling with coarse rubble) to receive waste water or STORMWATER and allow it to beslowly absorbed into the surrounding soil.
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The amount of water absorbed by a brick in one minute. Also called suction rate.
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In precise terms, refers to absorption by a transparent or translucent medium, per unit thickness. Often used erroneously, intended to mean ABSORPTANCE.
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A massive masonry or concrete structure which resists a THRUST.
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Abbreviation for ALTERNATING CURRENT.
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The Association for Computer- Aided Design in Architecture.
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Leaf of a Mediterranean plant used as decoration in Corinthian and composite order capitals and in scrolls, friezes, etc.
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Determination of the weather-resisting properties of materials (such as paints and plastics) by cycles imitating as closely as possible natural weathering conditions. Machines designed for this purpose are called WEATHEROMETERs
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The rate of change of velocity. The acceleration due to the earth’s gravity has a mean value of 9.807m/s2 (32.2ft/s2).
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A substance which speeds up a chemical reaction, as opposed to a RETARDER. (a) In concrete, an additive which increases the rate of hydration of the cement, and thus shortens the time of setting, or increases the rate of hardening or of strength development. (b) In synthetic resins or glues, a CATALYST which increases the hardening rate. The accelerator is mixed with the resin immediately before use.
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accelerometer, accelerograph
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An instrument for measuring, recording the acceleration of the body to which it is attached. The recorded time history of acceleration is an accelerogram.
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Lighting used to emphasise a particular part of the visual field. See also DIRECTIONAL LIGHTING.
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acceptable indoor air quality
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Indoor air that contains no contaminants in concentrations known to be harmful to human occupants and that is not offensive to a majority of people on initial entry to a space.
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