Glossary

Special thanks to the Portland Cement Association and the National Ready Mixed Concrete Association for providing some of the resources for these definitions.

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

A

ASR Alkali-silica reactivity refers to the chemical reaction that causes popouts. It occurs when silica or carbonates in the aggregate reacts with sodium oxides or potassium oxides in cement.

accelerator An admixture that shortens set-time by increasing the rate of hydration.

admixture Added to concrete’s three key ingredients (water, aggregate and cement). Admixtures include pigments to add color or chemicals to assist curing or hardening.

aggregate The sand or gravel that (with water and cement) is a key ingredient in concrete.

agitating speed Varying the rate of drum rotation of a concrete mixer can be significant since different mixes can require different speeds.

agitating truck Agitating the concrete in a truck en route from the concrete plant to the job site can result in more timely placement.agitation Gentle motion that keeps concrete from segregating or converting from its plastic state.

air-entrainment Refers to a state where concrete admixtures introduce tiny air bubbles during mixing. The bubbles in air-entrained concrete permit water to expand and contract during freeze/thaw cycles — without damaging the concrete. Contrast to air-entrapment.

air-entrapment Potentially harmful situation when larger and irregular air bubbles accidentally occur in concrete. Contrast toair-entrainment.

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B

bar spacing The distance between parallel reinforcing bars.

base The layer beneath a concrete slab, such as a driveway or basement floor. Effective preparation of the base improves the performance of the concrete.

batching The process for selecting, proportioning and mixing the ingredients in concrete.

bleed water Water that sometimes flows to the surface as concrete settles during curing.

blistering Improper finishing can result in the raising of a thin, unbonded layer (a "blister") at the surface of a concrete slab. Similar to but smaller than delamination.

bond Refers to the adhesion of cement paste to aggregate, as well as the adhesion of concrete to surface covers.

broom-finishing Using a boom to finish concrete can result in a textured surface that improves traction.

bush-hammer Concrete finishing tool with serrated face.

bug holes Accidental air-entrapment that occurs on the surface of formed concrete during placement and consolidation may result in small or irregular cavities.

bull float A large, flat rectangle (usually wood, aluminum or magnesium) used to smooth unformed surfaces of freshly placed concrete.burlap Using this coarse fabric on the surface of concrete is an effective way to retain water and improve curing.

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C

calcareous Containing calcium.

calcium chloride Useful as an admixture to accelerate curing, or as a deicing agent.

cast-in-place Concrete that is placed and cured at the site. Contrast to precast.

centrifugation A method of consolidation that uses centrifugal force.

cement A key ingredient of concrete (with water and aggregate) that binds the other ingredients. See portland cement.

cementitious A material able to act as a cement, including portland cement, fly ash, ground granulated slag and silica fume.

clinker The grayish-black pellets that become partially fused when the blended components of portland cement have been burned in a cement kiln.

compressive strength Ability to withstand direct force. Contrast with flexural strength.

concrete The rock-like mass that results from the combination of aggregate, cement and water.consistency The relative mobility or the ability of freshly mixed concrete to flow. Refers to concrete in its plastic state.

condensation The conversion of gas to liquid when it comes in contact with a cooler surface.

consolidation Reducing voids in freshly mixed concrete by promoting a closer arrangement of solid particles. Methods include centrifugation, rodding, tamping and vibrating.

construction joint The meeting of two successive placements of concrete.

contraction joint Intentionally creating a concrete joint (by forming, sawing, tooling a groove) can control the location of cracking.conveyor A device used to move material such as concrete ingredients during batching or aggregate from a gravel pit. Methods include a belt, an articulated system of buckets, a confined screw or a pipe.core test Taking a sample, cut from hardened concrete using a core drill, to test for compressive strength.

corrosion A chemical, electrochemical or electrolytic reaction that deteriorates metal. A cause of spalling.

crazing A fine mesh of superficial, hexagonal cracks.curing Ensuring optimum hydration by maintaining appropriate moisture and temperature for at least seven days.

curling The warping of a slab that occurs when curing concrete dries faster on the exposed surface (top) than the unexposed surface (bottom).

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D

d-cracking The series of cracks that form near and parallel to joints. Usually caused by freeze/thaw cycle and occurs only with certain aggregates.

darby A large, hand-operated straightedge that levels concrete before supplemental floating and finishing.

deicer Chemicals that are potentially harmful to concrete and used to melt ice or snow. Common ingredients include sodium and calcium chloride.

delamination The thin separation of a top surface of a slab of concrete. Primarily caused when premature troweling and sealing traps bleed water, air or both. This prevents bonding to the base slab. Similar to but bigger than a blister.

dowel A steel pin or bar which joins concrete slabs and transfers shear loads across the joint. It is bonded on only one side of the joint, freeing the joint to open and close.

durability Concrete’s unique ability to resist weather, corrosion, abrasion and other structural assaults.

dusting Refers to the powder that can develop at the surface of hardened concrete.

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E

efflorescence A cause of the white powder that can appear on concrete surfaces; occurs when soluble calcium hydroxides leach from concrete and react to carbon dioxide in the air to form insoluble calcium carbonates.

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

expansion joint The separation between two concrete slabs that accommodates the independent movement of each, sometimes filled with a compressible filler. Same as an isolation joint.

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F

fiber reinforcement An optional ingredient in concrete that adds randomly dispersed, performance-enhancing fibers.

finishing Treating fresh or just-placed concrete surfaces, often by trowling, texturing, broom-finishing or using a bull float.

flatwork Concrete floors and slabs that require finishing.

flexural strength Ability to withstand bending. Contrast with compressive strength.

floating A preliminary step when using a trowel for finishing.

fly ash Resulting from burning coal in electric plants and sometimes used as an ingredient in concrete.

fogging Maintaining the proper moisture for curing with a constant, fine mist.

form The cast into which concrete is poured. Forms may be used for cast-in-place and precast concrete. When forming a wall, they may be removed or, in the case of ICFs, left in place to form a permanent part of the structure.

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G

gravel Granular rock, conglomerate and other material used for aggregate. Technical definitions require that it be retained on the No. 4 sieve. Contrast to sand and silt.

groover Tool that forms grooves or weakened-plane joints in concrete.

grout A mixture of cement, sand and water. Different than concrete in that it does not contain gravel or other coarseaggregates.

gypsum A mineral that contains calcium sulfate dihydrate.

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H

hydration The chemical process by which water activates portland cement to bind with aggregate and form concrete.

hydraulic cement Cement that will set under water.

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I

ICF Stands for "insulated concrete form." A method of wall construction that uses stay-in-place forms that are reinforced with steel and filled with plastic concrete.

in situ See cast-in-place.

isolation joint See expansion joint.

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J

joint Strategic separations in concrete designed to reduce unintended cracking and buckling. Joints include construction,contraction, expansion, isolation and lift.

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K

kiln A furnace or oven that creates the extreme heat (2600 to 2700 degrees Fahrenheit) necessary to convert to clinker the ingredients in portland cement. Types of kilns include rotating, shaft, fluid-bed or traveling-grate. Usually fueled by coal, oil or gas.

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L

lift The concrete placed between two adjacent horizontal joints.

lift joint The surface at which two successive lifts meet.lime The general term for any of the chemical and physical forms of quicklime, hydrated lime and hydraulic hydrated lime. Technical definition is calcium oxide (CaO).

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M

map cracking Intersecting cracks, extending below the surface of hardened concrete. Caused by uneven shrinking during drying or by a chemical reaction between alkalis in cement and mineral in the aggregate within the hardened concrete.

marl A calcareous clay, common in Minnesota.

membrane curing Using a film (created by either a sealing compound or a non-liquid protective coating) to control evaporation during curing of freshly placed concrete.

mix Often refers to the specific mix of concrete.

mixer Machine that blends concrete ingredients.

moist Specifies not quite dry. When applied to concrete, the term differentiates from "wet" (which refers visible free water) and "damp" (which refers to a state between "wet" and "moist").

monolithic Describes concrete’s ability to result in a single, integrated mass.

mortar Cement paste and fine aggregate. Can refer to the material in the spaces between particles of coarse aggregate.

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N

O

P

peeling When mortar breaks away from concrete in thin flakes. Sometimes occurs when surface mortar sticks to forms.

placement Refers to the pouring and installation of concrete that is still in its plastic state.

plant-mixed Concrete in which the three ingredients were mixed a plant or batching facility. Compare to transit-mixed.

plastic Concrete in its workable and cohesive state.

plasticizer Admixture that enhances and prolongs workability or consistency of concrete.

porosity The ratio of concrete’s total volume to the volume of its voids. Usually expressed as a percentage.

portland cement The specific cementitious material invented and patented by Joseph Aspdin in 1824. Modern portland cement is made from the high-temperature conversion of limestone, clay, shale and other finely ground material into calcium, silica, aluminum and iron. Virtually all cement used in modern concrete is portland cement.

popout See ASR.

post-tensioning Adding tensioning tendons to prestress concrete after it has hardened. Compare to pretensioning.

pozzolan Although not inherently cementitious, this material may — when finely divided and combined with moisture — react with calcium hydroxide at normal temperatures to take on cementitious properties. Pozzolan contains siliceous, sometimes in combination with aluminous material. This was a key ingredient in the concrete used by the ancient Romans.

precast Concrete that is placed in forms and cured, then delivered to the site. Contrast to cast-in-place.

prestressing Technique that adds flexural and compressive strength by adding stresses that counteract the stress to be inflicted on the concrete.

pretensioning Prestressing concrete by imbedding tensioned steel in fresh concrete, then releasing the tension once the concrete has hardened.

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Q

R

reinforced concrete The addition of steel bars to fresh concrete. Once embedded, the bars work to increase the hardened concrete’s compressive and flexural strength. See prestressed and post-tensioned.

retarder Admixture that delays hardening of fresh concrete, mortar or grout.

rodding Using a tamping rod to aid consolidation. Also called tamping.

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S

salamander Portable heat source used during cold-weather concrete curing. Usually burns oils and is used with an enclosure. The resulting carbon dioxide often promotes dusting.

sand Fine granular material used for aggregate. Technical definitions require that it pass through the No. 4 sieve and be retained on the No. 200 sieve. Contrast to gravel and silt.

sand blast Using a high-speed stream of sand and water to clean concrete and other surfaces.

scaling When a shallow depth of a hardened concrete surface breaks away.

screed The act of striking off excess concrete to obtain the desired grade during placement of concrete. Also refers to the tool (sometimes referred to as a "strike-off") used to perform this task.

separation The tendency for coarse aggregate to separate from the rest of the mix during transportation. Most prevelant in non-air-entrained and high-slump concrete.

set Refers to the point at which concrete is no longer plastic. This arbitrary designation is measured in terms of resistance to penetration or deformation.

settling Concrete’s loss in elevation, resulting from sinking due to concrete’s weight or the loads imposed on it, or from shrinkage or displacement of the base. Compare to shrinking.shale This sedimentary rock — whose particles are found in clay and silt — is an ingredient in portland cement.

sieve A screen with regularly spaced apertures used to accurately measure and source particles such as the gravel and sand used as aggregate in concrete.

silica fume This blast-furnace byproduct is a fine, non-crystaline form of silica that can be used to manufacture portland cement.

silt Very fine granular material. Technical definitions require that it pass through the No. 200 sieve. Compare to gravel andsand.

shrinking The reduction in the actual volume of the concrete, as opposed to settling.slab A flat, horizontal molded layer of concrete.

slag Non-metallic waste product resulting during the manufacture of pig iron. Contains lime, silica and alumina. Useful in the manufacture of portland cement and as aggregate.

slump Refers to the consistency of freshly mixed concrete. Measures to the nearest _ inch that a molded specimen falls after removing a slump cone.slump cone A 12-inch cone used to measured slump. It has a 4-inch diameter at the top and an 8-inch diameter at the bottom.

shotcrete Concrete placed onto a surface by projecting pneumatically it through a hose at high velocity. Available as dry-mix shotcrete and wet-mix shotcrete.slurry A suspension in water of portland cement, slag, soil or other fine materials.

spalling The detatchment of a fragment from a larger mass. Potentially caused by a blow, harsh weather, pressure, expansion with the larger mass or corrosion.strikeoff See screed.

subgrade The soil prepared and compacted before placing concrete.

sulfate A chemical that can cause concrete deterioration. It is found in soil or ground water and can react to the calcium aluminate hydrates sometimes found in the cement-paste mix.

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T

tamping A method of consolidation that is similar to rodding.

texturing Producing a texture on hardened or unhardened concrete.

tilt-up Walls are cast onsite, horizontally, then tilted into position.

transit-mixed Concrete is batched at the plant, then mixed either on the way to, or at, the job. Compare to plant-mixed.

trowling Using a trowel to finish concrete. Used in the final stages, generally to impart a relatively smooth finish.

truck mixer A mixing drum, mounted on a truck to mix concrete in transit.

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U

ultimate load The heaviest load a structure can withstand.

ultimate strength The maximum resistance a structure can withstand.

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V

vapor barrier Placed-on-grade waterproof membrane that prevents transfer of water from subgrade to concrete.

vibration A method of consolidation that uses vigorous agitation of the freshly mixed concrete.

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W

water/cement ratio The ratio of the water weight to concrete weight.

workability The ease of placing, consolidating and finishing freshly mixed concrete.

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X

Y

yield Refers to the amount of concrete that results from a specific batch. In theory, multiple batches, each made with the exact same ingredients, should have consistent yields.

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Z