Glossary of Concrete Terms

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


Accelerator – A concrete additive that increases the rate of hydration, or hastens the setting time of concrete. Calcium chloride is an example.

Adjacent Paving – Sidewalk, curb and gutter, or paving that is formed against an existing pavement.

Admixture – Ingredients in concrete other than cement, water, and aggregates that are added during mixing to enhance its properties, control setting and early hardening, or improve workability. Admixtures include fly ash, accelerators, retarders, and superplasticizers.

Aggregate – Gravel or stone added to the concrete mixture. Includes gravel, crushed stone, sand, slag, or recycled crushed concrete.

Auger – Screw-type device used to transfer material. Our auger conveyor transports concrete to the mold. The auger on an extruder style curb machine also compacts the material as it pushes it into the mold.

Auto-Slope – Part of the machines control system that automatically adjusts the side to side angle of the machine/mold.

^ Back to top


Barrier – A boundary wall, many times with steel reinforcement inside the concrete structure. Typically used in highway medians to separate opposing traffic.

Base – The foundation of underlying ground, gravel, or asphalt on which concrete is placed. A properly prepared base helps to distribute loads, provides drainage, and minimizes frost action.

Binder – Hardened cement paste within the concrete mixture. It “glues” the fillers together to form a synthetic conglomerate. Also used to refer to the adhesive that ties extruded curb to the existing pavement.

Block-Out – A bolt-on accessory used to change the pouring width of a mold, usually in the gutter section of the mold. Also used to remove a feature such as a step on the back of the curb which supports a sidewalk.

Bolt-On Extension – A bolt-on accessory to increase the pouring height of a mold, typically used in pairs.

^ Back to top


Catch Curb – A curb and gutter that is placed so that water flows towards the gutter. Also referred to as wet curb or inflow.

Center Pour – A method of slip forming where the mold is mounted between the tracks, underneath the machine. Typically used for wider paving in order to minimize the overall width of the machine.

Charge Hopper – The tub at the lower end of the conveyor where a ready-mix truck discharges the concrete to supply the slip-form machine.

Contraction Joint – (See Joint) A joint, typically only partial depth, designed to control the natural cracking of the concrete as it shrinks during curing or due to variations in temperature.

Cross-Slope – The side-to-side angle of the machine, mold, or placed concrete. Its purpose in the finished paving is to help control and direct drainage in the proper direction.

Crown – Refers to a roadway that is not flat across its width, but is higher along the center-line such that water will flow off to both sides.

Cubic Yard – A typical unit of measure for the volume of concrete. 1 cubic yard = 0.76 cubic meters = 27 cubic feet. Sometimes simply referred to as a yard of concrete.

Cubic Meter – A typical unit of measure for the volume of concrete. 1 cubic meter = 1.31 cubic yards. Sometimes simply referred to as a meter of concrete.

Curb and Gutter – Edging for a street used to control water run-off. It incorporates both a vertical restraint and a horizontal flow channel that intersects the pavement.

Curing – The hardening of the concrete. It is important to maintain a satisfactory temperature and moisture content in freshly poured concrete in order to obtain the desired properties.

^ Back to top


Detachable Toe – A removable inner side plate of a mold that allows the gutter to be placed adjacent to existing pavement. When bolted in place, the same mold can pour stand-alone curb and gutter.

Driveway Knife – A curb mold accessory used to reduce labor and wasted material at driveway entrances. When engaged, it prevents material from filling the curb portion of the mold.

Entrained Air – Minute air bubbles induced into the concrete by a chemical additive. The air is helpful for increasing the concrete’s workability and allows for internal expansion during freeze/thaw cycles which adds to its durability.

Entrapped Air – Excess air that is unintentionally formed in concrete. This air creates undesirable voids that are detrimental to the structural integrity of the concrete. It is sometimes called honey-combing.

Expansion Joint – (See Joint) A joint permitting pavement to expand in length, due to variations in temperature. The joint usually contains a pre-formed soft material to cushion the edges of the concrete from expansion forces.

Extruder – A relatively small, powered machine that uses an auger to compact the material and force it through a mold to produce a uniform, free standing, high density curb. These walk-behind machines can handle either concrete or asphalt and place the curb on existing pavement or on a smooth, 95% compacted surface.

Fiber Reinforcement – Short and thin fibrous material within the concrete mixture used to increase its structural integrity. The fibers may be formed from materials such as glass, metal, or plastic and increase the strength and cracking resistance of concrete.

Fly Ash – Residue leftover from burning coal. It is used as a substitute for a percentage of the cement or as an additive to concrete to increase its workability. Is also called filler.

Form – A temporary structure of the desired shape for supporting concrete while it is setting and gaining sufficient strength to be self supporting. A curb machine is used to eliminate much of the need for building forms.

^ Back to top

G, H, I, J, K

Glare Screen – An additional concrete wall added to the top of a roadway barrier wall. It is used to block the headlights of oncoming traffic. (See Barrier)

Grade – The beginning surface, or base, on which the concrete is poured. Also referred to as sub-grade.

Hand Mule – A hand tool for finishing work, typically matching all or a portion of the shape of the placed concrete.

Header Curb – A curb only with no gutter. Also referred to as Stand-Up Curb or Ribbon Curb.

Hub – A survey stake or reference point used to establish the location for the curb and gutter or other structure.

Integral Curb – The vertical curb section that is poured at the same time as the roadway.

Jersey – Barrier wall terminology is many times prefixed with Jersey or New Jersey based on it being pioneered by the New Jersey Department of Transportation. (i.e. Jersey Face)

Joint – A necessary break built into a concrete structure designed to control the natural expansion and contraction of the concrete due to variations in temperature.

^ Back to top

L, M, N, O, P

Lock to Grade – Using a grade sensor such that it only senses and controls drift in machine elevation as opposed to sensing from a string line. In this setup, the concrete will be placed following the existing surface such as with rehabilitation work replacing the curb and gutter to match the existing pavement.

Mold – A metal form used on a curb machine to slipform the curb, curb and gutter, barrier wall, sidewalk, or other structure.

Monolithic – Typically refers to a sidewalk with an integral curb and gutter, poured as single structure. Can be used to refer to a mold as in Monolithic Curb, Gutter, and Sidewalk Mold.

Mule – Another term for mold. (See Mold)

Null – The zero or center set point on a sensor read-out.

Offset Position – Slipforming where the mold is mounted to the side of the curb machine, which is the typical pouring arrangement. The portion of our slipform curb machine where the mold mounts and by which is adjusted for proper positioning in relation to the machine is referred to as the offset.

Outflow Plate – A bolt-on accessory used to change a mold with a catch gutter into a spill gutter by reducing the height of the toe. (See Catch Curb and Spill Curb)

Overbuild – The deliberate raising of the outside edge of the concrete slab in anticipation of the concrete falling back into position once the mold passes. This is done by building the paving pan with a slightly raised edge or with a device to deflect it upwards when desired. (See Pan)

Pan – The forming section of a concrete slip form mold. This area is generally only referred to as a pan when it is wide and flat.

Parapet – Similar to a barrier, but used on bridges. The outside face is generally flat and close to vertical.

Permeable or Pervious Concrete – A special purpose concrete containing large voids which allow water to drain through freely.

Percent Slope – The measurement of the side-to-side angle of the machine, mold, or placed concrete. It is calculated by dividing rise by the run. (2% slope is approximately equal to ¼” of vertical rise per 12″ of horizontal run; .25 / 12 = .02 = 2%)

Porched Open Front – An opening in the front of a mold that allows steel to pass through when reinforcement is required inside the placed concrete. The opening includes a surrounding housing (the porch) to contain the concrete that escapes through the opening.

^ Back to top

R, S

Radius – Refers to curb poured around a fairly tight circle such around an island in a parking lot or in a median.

Rebar Port – A funnel shaped tube bolted through a hole in the front of a mold through which a single piece of rebar can be fed into the mold and embedded inside the placed concrete.

Retarder – A concrete additive that decreases the rate of hydration, or delays the setting of concrete and increases the time that fresh concrete is workable.

Roller Compacted Concrete (RCC) – A special mix of concrete that is very dry and has zero slump that is placed by conveyors or dump trucks, then compacted by vibratory rollers.

Scab-On – Curb placed on top of an existing pavement.

Screed – A separate piece of a mold shell of the same profile shape mounted on the trailing end. It is used for final finishing of the product after having let air escape through the gap where it attaches to the mold.

Sensor – The component on a slipform machine that receives guidance from the stringline (or other external signal) used to control the steering and elevation of the machine.

Ski/Skate – An attachment for the sensor that allows it to ride directly on a wall, pavement, or any surface that you want the machine to follow. Its use can eliminate the process of setting a stringline. (See Sensor and Stringline)

Slag – The ground material leftover from the production of metals. It is used as an additive in concrete to increase properties such as durability and to reduce its permeability.

Slipform Paving – The continuous method of placing concrete using a machine guided mold and vibration to confine and finish the concrete. (See Mold and Vibrator)

Slope – (See Cross-Slope)

Slump – A physical property measurement of a concrete mixture. It is used as an indicator of the fluidity and workability of the mix. A tool called a slump cone is used for the measurement. It is the difference between the height of the cone and that of the specimen as measured immediately after the cone is removed.

Spill Curb – A curb and gutter that is placed so that water flows away from the curb. Also referred to as dry curb or outflow.

Straddle Leg – Part of the slipform machine structure that allows one of the crawlers to be extended away from the machine for increased stability or to be retracted for transport. Also, it allows the machine to center pour. (See Center Pour)

Straight Edge – The tool used to check the flatness of placed concrete, it is often a 10-foot (3m) long straight bar. It can be used to screed, or strike off and level, wet concrete and to correct minor deviations.

Stringline – A cord held in place by a system of stakes and clamps, used to guide automatic equipment such as a paver or curb machine for both steering and elevation. A stringline is a parallel reference to a surveyors hubs. (See Hub)

Sub-Grade – The beginning surface, or base, on which the concrete is poured. Also referred to as grade.

Superplasticizer – A water reducing concrete additive that increases the slump of concrete without having to increase the water content. Also used to maintain concrete workability with a reduced amount of water.

^ Back to top

T, V, W, Y

Trim and Pour – The process of simultaneously cutting the sub-grade to final dimensions and placing concrete. (See Trimmer)

Trimmer – A rotating device with replaceable teeth used to cut and remove excessive sub-grade to the proper dimension in preparation for paving. (See Sub-Grade) Also referred to as fine trimmer.

Transition – A gradual change in the cross-slope of placed concrete. With curb and gutter, it may gradually change from catch to spill as a transition. In highway paving, it may gradually change between crowned, flat, and cross slope as a transition. (See Cross-Slope, Catch Curb, Spill Curb, and Crown)

Variable Barrier – A barrier used for dividing roadways that are on differing grades. A variable barrier mold is built with one or both adjustable jersey faces. (See Barrier and Jersey)

Vibrator – A device used to agitate fresh concrete so that it will properly fill the mold and to consolidate the concrete.

Wear Plates – A bolt-on replaceable section at the bottom of a mold shell, typically used in pairs.

Yard – Sometimes referred to for cubic yard. (See Cubic Yard)

Yield – The volume of concrete required (theoretical) to fill the dimension being poured. The deviation from theoretical is the yield loss or gain.
^ Back to top