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ACCELERATOR- Substance added to concrete to increase the rate of hydration.
AGGREGATE- Gravel, limestone and sand.
AIR-ENTRAINED CONCRETE- Concrete containing microscopic air bubbles generated by the use of an air-entraining admixture to improve resistance to freezing and thawing.
ARCHITECTURAL CONCRETE- Concrete left exposed to view.
BLEEDING- The rising of water to the surface of freshly placed concrete.
BLISTERS- Shallow dome shaped surface defects on a flat surface. Created when entrapped air bubbles rise and swell a thin layer of surface concrete.
BUNGHOLES- Surface defects created when air voids are entrapped and retained next to the surface of the form.
BULL FLOAT- A long handled tool with a broad rectangular face of wood or magnesium, used after screeding to smooth unfinished concrete.
CONCRETE SHRINKAGE- Loss of volume over time, as chemical changes occur and water escapes from the concrete.
CONSISTENCY- The ability of a plastic concrete mix to hold its shape. Measured by the slump test.
CONTROL JOINT- Formed, sawed or tooled groove made in a concrete surface to force concrete to form a crack underneath the joint rather than elsewhere when it shrinks or contracts.
CRAZING- The overall pattern of random hairline cracks in a concrete surface caused by drying shrinkage stresses. It is usually caused by an excess amount of fines on the surface.
CROWN- The slight elevation of the center of a slab created to allow the surface to drain.
CURING- Maintaining favorable temperature and moisture in concrete for an adequate period of time, beginning as soon as possible after finishing.
DARBY- A long wood or magnesium float attached to an angled rigid handle to permit middle-distance smoothing. Darbying follows screeding and precedes floating. A darby is often used instead of a bull float.
DEICER- Usually salt or calcium chloride. Also urea can be used.
DRY-SHAKE- A dry mixture of cement with special mineral or metallic aggregate used to produce a hard surface.
DUSTING- The appearance on the surface of hardened concrete of a powdery material coming from the concrete itself.
EDGER- Finishing tool used on plastic concrete to make rounded corners on the edges of slabs or steps.
ENTRAPPED AIR- Large, visible and undesirable air voids that become imprisoned in concrete during mixing and placing.
EXPOSED AGGREGATE SURFACE- Concrete in which coarse aggregate near the surface has been revealed by removal of surface mortar, usually before complete hardening has taken place.
FALSE SET- The premature stiffening of a plastic concrete mix. Renewed mixing causes it to disappear.
FINISHING- Operations designed to bring a surface to its desired plane, hardness and texture
FLATWORK- Broad designation of any horizontal or nearly horizontal concrete pavement, slab or floor in which the top surface is not shaped by form work.
FLOAT- Tool composed of a handgrip fixed to the back of a wood or magnesium face and used to achieve an open-textured finish. Floating is done after darbying or bull-floating and before troweling.
FLOAT SHOES- Detachable blades used on power troweling machines. They should be used before troweling.
FORM RELEASE AGENT- An oil or chemical coating applied to inside form surfaces to prevent concrete from adhering to forms as it sets.
GRADATION- The proportion of various sizes of coarse and fine aggregates in a mix. Optimization of gradation achieves optimal strength, economy, workability, shrinkage and other properties.
GRADE STAKES- Used to place wet screeds, the tops of the stakes are set at the desired elevation of the finished slab.
GROUT- A fluid mixture of Portland cement and water, with or without fine aggregate.
HONEYCOMB- A defect occurring in concrete when mortar fails to fill the voids between the coarse aggregate particles.
HYDRATION-The chemical reaction in which Portland cement combines with water to produce compounds that bond together the aggregates in concrete.
JITTERBUG- Tamper, usually consisting of a grillwork of bars or expanded metal, for pushing coarse aggregate below the surface of plastic concrete to facilitate finishing. This tool should be used on low-slump concrete (2 inches or less).
KNEE BOARD- Flat rectangular board for the cement finisher to kneel on. It supports his weight as he moves over the surface of a slab during hand finishing.
LAITANCE- A weak, milky layer of cement and sand that rises to the surface of over wet concrete and mixes with bleed water, usually as a result of premature finishing.
MESH- Welded wire fabric. When used properly in flatwork, it keeps cracks tightly closed.
MORTAR- In concrete work, the mixture of cement paste and fine aggregate.
NEAT CEMENT- Cement to which no aggregates have been added. Neat cement grout or neat cement past is a mixture of just cement and water.
NORMAL WEIGHT CONCRETE- Concrete weighting about 150 pounds per cubic foot.
PATTERN STAMPING- The use of tools with patterned faces to impress lines of a design into troweled surfaces.
PLASTIC CONCRETE- Concrete that is still workable.
PONDING- Confining water with dikes on level slabs to promote curing.
POST WETTING- Covering plastic concrete with wet burlap following darbying or bull-floating in order to prevent cracking
POST-TENSIONING- Pre-stressing reinforced concrete in which tendons are tensioned after the concrete has hardened.
PRE-STRESSED CONCRETE- Concrete in which internal stresses are introduced to counteract the tensile stresses resulting from the service loads to a desired degree.
REINFORCEMENT- Rods, bars, mesh or fibers embedded in such a way that the concrete and the reinforcement act together to resist stresses.
SCALING- The flaking away of the surface of a hardened concrete slab to a depth of about 1/16 to 3/16 inch, but it can be much deeper with loss of coarse aggregate.
SCREED- A strip of material or side form set to finished grade and used as a guide when material such as fresh plaster or concrete is straightedged.
SEGREGATION- A separation of coarse and fine materials in fresh concrete resulting in nonuniformity. Sand and cement fines may also segregate at the surface.
SLUMP- A measure of the consistency of freshly mixed concrete made by measuring the loss of height on a compacted sample when the mold, or regulation dimensions, is removed.
STICKY MIX- (TACKY-MIX) A mix too high in fines or low in entrained air, which can make it too cohesive for good workability.
TROWEL- A flat, steel-faced hand tool used to bring a concrete surface to the desired smooth finish.
UNIT WEIGHT- The weight
of one cubic foot of fresh concrete, or dry cement, aggregate or other
concrete ingredient, after compaction by rodding.