Glossary of Precast Terms

Glossary of Precast Terms

A

Architectural Precast Concrete
A precast product with a specified standard of uniform appearance, surface details, color and texture

Accelerated Curing
The intentional addition of heat to the concrete environment to expedite curing

Admixture
A material other than water, aggregate and cement used as an ingredient in concrete, mortar or grout to impart special characteristics

Ambient Temperature
The temperature of the air surrounding the precast molds into which the concrete is cast


B

Batching
The process of weighing or volumetrically measuring and introducing into the mixer, the ingredients for a batch of concrete

Bleeding
A form of segregation in which some of the water in a concrete mix rises to the surface of freshly placed concrete

Bug holes
Small holes on the formed concrete surfaces formed by air or water bubbles. Also known as blowholes


C

Cladding/Non-load-bearing panel
A wall unit that resists only wind or seismic loads and its own weight.

Compaction
The process whereby the volume of the concrete is reduced to the minimum practical space by the reduction of voids usually obtained through vibration, tamping, or a combination of both

Connections
A structural assembly or component that transfers forces from one precast concrete member to another or from one precast concrete member to another type of structural member

Corbel
A projection from the precast member designed to support vertical and horizontal forces as required. It is also called a Haunch

Crack
A visible separation of the concrete at the surface

Curing
The maintenance of moisture and temperature within freshly placed concrete during some defined period following placing, casting or finishing to assure satisfactory hydration of the cementitious materials and proper hardening of concrete


D

Dollie
Axled apparatus used to support the back end of a long precast member during the hauling process

Dry mix concrete
A concrete designed with low water-cement ratios and slump. Often referred to as zero slump concrete

Ductility
The ability to accommodate relatively large deformations without failure

Dunnage
Materials used for keeping concrete elements from touching each other during storage or transport


E

Exposed aggregate concrete
Concrete manufactured so that the aggregate on the face is left protruding

Efflorescence
A whitish, powdery residue on the surface of concrete


F

False Joint
Scoring on the face of a precast concrete panel, used for aesthetic or weathering purposes and normally made to simulate an actual joint

Fly ash
A finely divided residue with pozzolanic properties that results from the combustion of ground or powdered coal and that is transported by the flue gases


G

Grout
A mixture of cementitious materials and water, with or without sand or admixtures

Gap graded concrete
A mix with one or a range of normal aggregate size eliminated, and/or with a heavier concentration of certain aggregate sizes over and above standard grading limits. It is used to obtain a specific exposed aggregate finish

GGBS
Ground Granulated Blast Slag. It is a fine, granular, mostly latent hydraulic binding material that can be added to SCC to modify the rheological properties of the materials


H

Honeycomb
Stoney or void areas in the concrete due to incomplete consolidation or paste leakage from the mold. May vary from small to large in size.


L

Ledge
A continuous corbel on a beam

Lifting anchors
Cast-in devices used to lift precast panels

Load-bearing precast panel
Precast panels which form the integral part of the building structure and which are essential to its stability. They resist and transfer loads applied from other elements. Therefore, they cannot be removed without affecting the strength or stability of the building


M

Man hours
Man hours specify how many workers are necessary on average in order to produce one square meter of precast concrete elements per hour.

Mold
Also known as Form. It is a container or surface against which fresh concrete is cast to give it a shape

Mold face or formed face
A concrete surface that has been cast mold or form face

Mold release agent
A substance applied to the mold for the purpose of preventing bond between the mold and the concrete cast

Modulus of elasticity
Ratio of normal stress to corresponding strain for the tensile or compressive stresses within the elastic limit of material


P

Powder
Materials of particle size passing the No. 100 sieve (0.15 mm)

Plastic cracking
Short cracks often varying in width along their length that occur in the surface of fresh concrete soon after it is placed and while it is still plastic

Production drawings
Also known as Fabrication drawings or shop drawings. They are a set of instructions in the form of diagrams and text containing all the information necessary for the manufacturer to produce the precast element. Shop drawings is sometimes a collective term used for erection drawings, production drawings and accessories or hardware drawings


R

Response spectrum
Relates to the maximum responses (acceleration, velocity or displacement) of a structure to its natural frequency of vibration or period

Retarder
An admixture which delays the setting of cement paste and therefore the concrete

Return
A projection that angles away from the main face or plane of view

Retempering
The addition of water or admixture and remixing of concrete which has started to stiffen in order to make it more workable


S

Sandwich wall panel
A wall panel consisting of two layers (Wythes) of concrete fully or partially separated by insulation

Segregation
The tendency for the coarse particles to separate from the finer particles during handling

Self-compacting concrete (SCC)
Concrete that can flow around reinforcement and consolidates under its own weight without additional effort and without exceeding specified limits of segregation

Spreader beam
A frame of steel channels or beams attached to the back of a panel, prior to stripping, for the purpose of evenly distributing loads to inserts and lifting the panel about its center of gravity

SSD
Standard abbreviation for the concrete aggregate moisture condition of saturated, surface dry

Spall
A fragment of concrete broken away from the mass

Specific gravity
The ratio of the weight of a given volume of a substance to the weight of an equal volume of water

Stack casting
A method where one member is cast directly on top of the other

Stripping
The process of removing a precast concrete element from the mold/form in which it was cast

Structural integrity
The quality of a structure which allows stresses to be transferred from one component of a structure to another component

Super plasticizer
A high range water reducing (HRWR) admixture that produces concrete of significantly higher slump without addition of water

Surface retarder
A material or chemical used to retard or prevent the hardening of the cement paste on a concrete surface to facilitate removal of this paste after curing. This is primarily used to produce an exposed aggregate finish


T

Tolerance
Specified permissible variations from stated requirements such as dimensions, locations, alignment, strength etc. Production tolerance are those variations in dimensions relating to individual precast concrete members. Erection tolerances are those variations in dimensions required for accepting matching of precast member after erection. Interfacing tolerances are those variations in dimensions associated with other materials in contact with, or in close proximity to, precast concrete


Q

Quality Control
Those actions related to the physical characteristics of the materials, processes and the services, which provide a means to measure and control the characteristics to predetermined quantitative criteria


W

Wet mix concrete
A concrete designed for typical water-cement ratios, slumps and handling and consolidation methods

Workability
The ease with which a given set of materials can be mixed into the concrete and subsequently handled, transported, placed and finished with a minimum loss of homogeneity