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AAC - Autoclaved Aerated Concrete  Exceptionally lightweight precast concrete with high thermal qualities and fire resistence.  Suitable for cutting with ordinary hand tools.  Mix design is composed of portland cement, sand or siliceous material, lime, gypsum, finely powdered aluminum, and water.  Initial mix is a combination of portland cement, sand, lime and gypsum to produce a slurry.  Finely powdered aluminum mixed into a paste is added prior to placement into large, rail-like forms.  The finely powdered aluminum reacts with the alkaline components of the cement and lime to produce hydrogen gas, which increases the volume approximately five times producing a uniformly, dispersed cellular structure.  Units are cut to required shape.  Units are placed in an autoclave, an enclosed pressurized chamber, and steam cured at 350⁰ F.  Approximately 80% of the ultimate volume consists of air voids.

Abrasion Resistance  Resistance of a surface of being worn away by friction or rubbing process.

Absolute Volume The volume of an ingredient in its solid state, without voids between individual pieces or particles, in the case of fluids, the cubic content occupied. In concrete, the actual volume occupied by the different ingredients determined by dividing the weight of each ingredient pounds, by ifs specific gravity, times the weight of one cubic foot of water in pounds. Example: Absolute Volume of one sack of cement equals:  94 ÷ (3.15X62.4) = 0.478 cubic feet

Absorbed Moisture Moisture which is mechanically held in a material.  In aggregates, that water which is not available to become part of the mixing water is designated "absorbed" water.

Absorption The process by which water is absorbed.  The amount of water absorbed under specific conditions, usually expressed as percentage of the dry weight of the material.

Accelerator An admixture which, when added to concrete, mortar, or grout, increases the rate of hydration of the hydraulic cement, shortens the time of set and increases the rate of hardening or strength development,

Adiabatic Curing The maintenance of ambient conditions during the setting and hardening of concrete so that heat is neither lost nor gained from the surroundings of the concrete.

Admixture A material other than water, aggregates, and portland cement that is used as an ingredient of concrete, and is added to the batch immediately before or during the mixing operation.

Adsorption Water  Water held on surfaces in a material by either physical and/or chemical forces. 

Air Content The amount of entrained or entrapped air in concrete or mortar, exclusive of pore space in aggregate particles, usually expressed as a percentage of total volume of concrete or mortar.

Air Entraining Agent An addition for hydraulic cement, or an admixture for concrete or mortar which entrains air in the form of minute bubbles in the concrete or mortar during mixing.

Alkali-Aggregate Reaction Older terminology for Alkali-Silica Reactivity (ASR).

ASR - Alkali-Silica Reactivity The reaction of aggregates, which contain some form of silica or carbonates with sodium oxides or potassium oxides in cement, particularly in warm, moist climates or environments, causing expansion, cracking or popouts in concrete.

Aluminous Cement A hydraulic cement in which the principal constituents are calcium aluminates, instead of calcium silicates which comprise the major ingredients of portland cement. (See calcium aluminate cement)

Autoclave A chamber in which an environment of steam and high pressure is produced.  Used in curing of concrete products and in the testing of hydraulic cement for soundness.

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