Dispersing Agent An admixture capable of increasing the fluidity of pastes, mortars, or concretes by reduction of interparticle attraction.

Dry Rodded Weight The weight of dry aggregate rodded into a cylindrical container of diameter approximately equal to the height, each of 3 layers rodded 25 times, and the excess aggregate struck off level with the top of the container

Drying Shrinkage A decrease in the volume of concrete upon drying.

Durability The ability of concrete to resist weathering action, chemical attack, and abrasion.

Efflorescence A crystalline deposit of salts which leach from the concrete as soluble calcium hydroxides and within a short period of time will combine with the atmospheric carbon dioxide to form insoluble calcium carbonates, usually white in color, appearing on the surfaces of masonry, stucco or concrete.

Elastic Shortening The shortening of a member in pre-stressed concrete which occurs on the application of forces induced by prestressing.

Entrained Air (See air entrainment) Microscopic air bubbles intentionally incorporated in mortar or concrete, to improve workability and durability (usually imparting a higher degree of resistance to freezing and thawing).

Entrapped Air Air in concrete which is not purposely en-trained, Entrapped air bubbles are normally much larger and more irregular than entrained air bubbles.

False Set The rapid development of rigidity in a mixed portland cement paste, mortar, or concrete without the evolution of much heat. This rigidity can be dispelled and plasticity regained by further mixing without addition of water.  Premature stiffening, and rubber set are terms referring to the same phenomenon, but false set is the preferred term.

Fine Aggregate  Aggregate passing the 3/8-in. sieve and almost entirely passing the No.4(4.76 mm) sieve and predominantly retained on the No. 200 (74 micron) sieve(ASTM125).          

Fineness Modulus An index of fineness or coarseness of an aggregate sample. An empirical factor determined by adding total percentages of an aggregate sample retained on each of a specified series of sieves, and dividing the sum by 100.  Note: US Standard sieve sizes are used: No. 100, No.50, No. 30, No. 16, No. 8, and No. 4, and 3/8 in., 3/4 in., I in.,  2 in., 3 in., and 6 in.

Flash Set The rapid development of rigidity in a mixed portland cement paste, mortar or concrete usually with the evolution of considerable heat, which rigidity cannot be dispelled nor can the plasticity be regained by further mixing without addition of water Also referred to as quick set or grab set.

Flexural Strength A property of a solid that indicates its ability to withstand bending.

Fly Ash The finely divided residue that results from the combustion of ground or powdered coal, transported from the firebox through the boiler by flue gases.

Foam Concrete (See Cellular concrete)

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