Concrete Terms Glossary
Plain-English definitions of the words you will meet when you buy, order and pour concrete. Terms link to the guides and calculators where they are used.
How to use this glossary
There are 59 terms below, grouped alphabetically. Each one has its own anchor, so you can link to a definition directly. Where a term is explained in more depth in a guide or a calculator, there is a link.
Terms A–C
- Admixture
- A material added to concrete at the plant or on site to change its behavior, such as a water reducer, retarder, accelerator or air-entraining agent.
- Aggregate
- The sand and stone that make up most of the volume of concrete. Fine aggregate is sand. Coarse aggregate is gravel or crushed stone.
- Air entrainment
- Microscopic air bubbles deliberately added to the mix to protect concrete from freeze-thaw damage.
- Base
- The compacted layer of crushed stone or gravel under a slab. It supports the concrete and drains water away.
- Bleed water
- Water that rises to the surface of freshly placed concrete as the solids settle. Finishing must wait until it has gone.
- Bull float
- A wide, flat tool on a long handle, used to smooth and level the surface right after screeding.
- Bulking
- The increase in the volume of sand when it is damp, caused by a film of water around the grains.
- Cement
- The fine powder, usually Portland cement, that binds the other ingredients together when mixed with water. It is not the same as concrete. See concrete vs cement vs mortar.
- Chair
- A small plastic or wire support that holds rebar or mesh off the base at the right height.
- Cold joint
- A joint where fresh concrete is placed against concrete that has already begun to harden, creating a weak plane.
- Compressive strength
- The load per unit area concrete can carry before it crushes, measured in psi or MPa. See the PSI guide.
- Concrete
- A mixture of cement, water, sand and coarse aggregate that hardens into a stone-like material.
- Consolidation
- Removing trapped air from fresh concrete by vibration, rodding or tamping so that it fills the form without voids.
- Construction joint
- A planned stopping point between two separate pours, often with a key or dowels.
- Control joint
- A groove cut or tooled into a slab so that shrinkage cracks form along it. See control joints.
- Cover
- The thickness of concrete between reinforcing steel and the nearest surface.
- Cubic yard
- A volume of 27 cubic feet (0.7646 m³). The unit in which ready-mix is sold in the United States.
- Curing
- Keeping concrete moist and at a suitable temperature so it gains strength. See curing time.
- Curing compound
- A liquid sprayed on after finishing to form a membrane that holds moisture in the slab.
Terms D–H
- Dobies
- Small concrete blocks used to hold reinforcement at the right height in a slab.
- Edger
- A hand tool that rounds the edges of a slab so they resist chipping.
- Efflorescence
- A white, powdery deposit of salts left on the surface when water moving through concrete evaporates.
- Float
- A flat tool used after screeding to embed the aggregate and smooth the surface before troweling.
- Footing
- The widened base of a wall, column or pier that spreads load into the soil. See the footing calculator.
- Form
- A temporary mold, of boards, plywood or tubes, that shapes the concrete until it has hardened. See formwork basics.
- Frost line
- The depth to which the ground freezes in winter. Footings in cold climates must extend below it.
- Grade
- The level of the ground or the surface of a slab. To grade is to shape the ground to the right elevation and slope.
- Grout
- A fluid mixture of cement, sand or aggregate and water used to fill voids, such as the cores of reinforced block walls.
- Honeycombing
- Voids in hardened concrete where mortar did not fill the spaces between coarse aggregate, caused by poor consolidation.
- Hydration
- The chemical reaction between cement and water that makes concrete harden and gain strength.
Terms I–R
- Isolation joint
- A full-depth gap with compressible filler that separates a slab from walls, columns or footings.
- Lap splice
- An overlap of two rebars to transfer load from one to the other, typically 30 to 40 bar diameters.
- Mix design
- The specified proportions of cement, water, aggregates and admixtures for a given strength and use.
- Mortar
- A mixture of cement, sand, lime and water used to bond masonry units. It contains no coarse aggregate.
- Pea gravel
- Small, rounded stone, about 3/8 in, used as drainage fill or as a coarse aggregate in small mixes.
- Plastic shrinkage cracking
- Short surface cracks that form in fresh concrete when water evaporates faster than it bleeds to the surface.
- Portland cement
- The most common hydraulic cement, made by heating limestone and clay and grinding the result.
- PSI
- Pounds per square inch, the unit in which concrete strength is quoted in the United States.
- Pump
- A machine and boom or hose that moves concrete from the truck to the forms.
- Ready-mix
- Concrete that is batched at a plant and delivered in a mixer truck in a fresh state. See how to order ready-mix.
- Rebar
- Steel reinforcing bar with ribs, sized by number in eighths of an inch. See rebar spacing and size.
- Release agent
- A coating on the form face that stops the concrete from sticking to it.
Terms S–Z
- Scaling
- Flaking of the surface of hardened concrete, often caused by freeze-thaw cycles and deicing salts.
- Screed
- A straight board or beam dragged across the forms to strike off the concrete to the right level.
- Set
- The stiffening of fresh concrete. Initial set is when it can no longer be worked; final set is when it has hardened.
- Short load
- A ready-mix order below the plant’s minimum, which carries an extra fee.
- Slab on grade
- A concrete slab that rests directly on the ground, such as a patio, garage floor or driveway.
- Slump
- A measure of the consistency of fresh concrete, from the drop of a cone-shaped sample in inches.
- Sonotube
- A brand of cardboard round forms for piers and columns. See the Sonotube calculator.
- Spalling
- Chipping or breaking away of concrete pieces from the surface.
- Stamped concrete
- Concrete with a pattern pressed into the surface while it is still plastic.
- Sub-grade
- The natural or prepared soil beneath the base.
- Trowel
- A flat steel tool used for a smooth, dense surface once the concrete has begun to stiffen.
- Vapor barrier
- A plastic sheet under a slab that slows moisture from the ground moving up into it.
- Washout
- Rinsing the mixer and chute after delivery, which must be done in a designated place.
- Water–cement ratio
- The weight of water divided by the weight of cement in a mix. Lower is stronger. See mix ratios.
- Welded wire reinforcement
- A grid of steel wires welded at the intersections, sold in sheets or rolls, used in slabs.
- Workability
- How easily fresh concrete can be placed, consolidated and finished.
- Yield
- The volume of finished concrete made by a bag of dry mix, printed on the bag. See bags per yard.
Units and abbreviations
| Abbreviation | Meaning |
|---|---|
| ft, in, yd | Feet, inches, yards |
| ft³, yd³, m³ | Cubic feet, cubic yards, cubic meters |
| lb, kg | Pounds, kilograms |
| psi, MPa | Pounds per square inch, megapascals |
| w/c | Water–cement ratio |
| CMU | Concrete masonry unit, a concrete block |
| ACI, ASTM, PCA, NRMCA | Industry bodies and standards organizations cited in our sources |
Frequently asked questions
What is the difference between cement and concrete?
Cement is the binder. Concrete is cement, water, sand and stone.
What does slump mean?
It is a measure of how stiff fresh concrete is.
What is a cold joint?
A weak joint between two pours when the first had begun to harden.
What is PSI in concrete?
The compressive strength, in pounds per square inch.
What is a control joint?
A groove that makes a slab crack in a straight line.
What is bleed water?
Water that rises to the surface of fresh concrete.
Sources
Estimate only. Results depend on the numbers you enter, ground conditions and your supplier. For structural work consult a licensed engineer and follow local codes. Brand names such as Quikrete and Sakrete are used only to cite published product data. This site is not affiliated with any brand.