Select the letter of a term you would like defined. You may select any letter section of the glossary from any glossary page.

• Reactive Aggregate - See Alkali-Aggregate Reaction.
• Rebound - Wet shotcrete or sand and cement which bounces away from a surface again at which pneumatically applied mortar is being projected.
• Refractory Concrete - Concrete having refractory properties, suitable for use at high temperatures. Calcium-aluminate cement and refractory aggregates are normally used for the manufacture of this product.
• Reinforced Concrete - (1) Concrete in which reinforcement, other than that provided for temperature changes for shrinkage, has been embedded in such a manner that the two materials act together in resisting forces. (2) Concrete in which steel bars have been placed to sustain the tensile stresses.
• Retardation - Delaying the hardening or strength gain of fresh concrete, mortar or grout.
• Retarder - An admixture which extends the setting time of cement paste, and therefore of mixtures such as concrete, mortar, or grout.
• Retempering - The addition of water and remixing of concrete which has started to stiffen: usually not allowed as it may affect the ultimate strength.
• Revibration - Delayed vibration of concrete that has already been placed and consolidated. Most effective when done at the latest time a running vibrator will sink of its own weight into the concrete and make it plastic and workable again.
• Rock Pocket - Area or portion of hardened concrete which is deficient in mortar and consisting primarily of coarse aggregate and open voids; caused by insufficient consolidation or separation during placement, or both; by leakage from form.
• Rod (tamping) (ASTM C 241) - A round, straight steel rod, 5/8" in diameter and approximately 24" in length, having the tamping end rounded into a hemispherical tip, the diameter of which is 5/8".
• Sack - A quantity of cement: 94 Ibs. in the United States, 87.5 Ibs. in Canada, for portland or air entraining portland cement, or as indicated on the sack for other kinds of cement.
• Sacking - Removing or alleviating defects on a concrete surface by applying a mixture of sand and cement to the moistened surface and rubbing with a coarse material such as burlap.
• Sand (ASTM C 125) - That portion of an aggregate passing the No. 4 (4.76 mm) sieve and predominantly retained on the No. 200 (74 micron) sieve.
• Sand Blast - A system of abrading a surface such as concrete by a stream of sand, or other abrasive, ejected from a nozzle at high speed by water and/or compressed air.
• Saponification - The deposit of a gray scum or gray dust on the inside surface of a subgrade wall or floor; as the result of moisture moving through the concrete and washing certain chemicals from the concrete mass.
• Scaling - The breaking away of a hardened concrete surface, usually to a depth of 1/16" to 3/16".
• Screed - (1) Firmly placed grade strips or side forms which are set as guides for a straight edge to bring the surface of concrete to the required elevation. (2) To strike off concrete above the desired level.
• Screen (or Sieve) - A metallic sheet or plate, woven wire cloth, or similar device, with regularly spaced openings of uniform size, mounted in a suitable frame or holder for use in separating material according to size.
• Segregation - The tendency for the coarse particles to separate from the finer particles in handling. In concrete, the coarse aggregate and drier material remains behind and the mortar and wetter material flows ahead. This also occurs in a vertical direction when wet concrete is over vibrated or dropped vertically into the forms, the mortar and wetter material rising to the top. In aggregate, the coarse particles roll-to the outside edges of the stockpile.
• Set - A term used to describe the stiffening of cement paste; a condition reached by a concrete, cement paste, or mortar when plasticity is lost to an arbitrary degree, usually measured in terms of resistance to penetration or deformation. Initial set refers to first stiffening; final set refers to attainment of significant rigidity.
• Setting Time - The time required for a specimen of cement paste, mortar or concrete, prepared and tested under standardized conditions to attain a specified degree of rigidity with particular reference to initial and final setting time.
• Shotcrete - Mortar or concrete conveyed through a hose and projected pneumatically at high velocity onto a surface; dry-mix shotcrete (gunite), and wet-mix shotcrete.
• Sieve - See Screen.
• Sieve Analysis - Determination of the proportions of particles of The granular material lying within certain size ranges on sieves of different size openings.
• Slip Form - A form which is raised or pulled as concrete is placed; may move vertically to form wails, stacks, bins or silos, usually of uniform cross section from bottom to top; or a generally horizontal direction to lay concrete evenly for highways, on slopes and inverts of canals, tunnels, and siphons.
• Slump - A measure of the consistency of plastic concrete relative to the amount it falls when a slump cone filled with concrete is lifted vertically. The slump cone is then placed beside the specimen of concrete and the number of inches from the top of the cone to the top of the of specimen of concrete is the slump (see ASTM C 143).
• Slump Cone - A metal mold in the form of a truncated cone with a top diameter of 4", a bottom diameter of 8", and a height of 12", used to fabricate the specimen for a slump test.
• Slurry - A mixture of water and such finely divided materials, such as portland cement, slag, or soil in suspension.
• Spall - A fragment, usually of flaky shape, detached from a larger mass by pressure, expansion from within the larger mass, a blow, or by the action of weather.
• Specific Gravity - The ratio of the weight of a material at a stated temperature to the weight of the same volume of gas-free distilled water at a stated temperature.
• Stucco - A portland cement mortar material that can be applied to the surface of any building or structure to form a hard and durable covering for the exterior wails or other exterior surfaces.
• Sulfate Attack - Deleterious chemical and/or physical re-action between sulfates in ground water or soil and certain constituents in cement, which result in expansion and disruption of the concrete.
• Sulfate Resistance - Ability of cement paste, aggregate, or mixtures thereof to withstand sulfate attack.
• Surface Moisture - Free moisture retained on the surfaces of aggregate particles which becomes part of the mixing water in the concrete mix.

Contributions: Kaiser Cement, Portland Cement Association, Concrete Manual, Bureau of Reclamation, U. S. Department of the Interior and many other publications, with special thanks to Bob Cameron of W. R. Meadows. © 2008 Moxie International, Inc. All Rights Reserved.

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