Cement Is the Binder; Concrete Is the Building Material

Cement is a binder. Concrete is the building material made by combining cement, water and aggregates such as sand, gravel or crushed stone. A footing, slab or wall calls for concrete—not straight cement.

In ordinary construction, the cement in concrete is usually hydraulic cement, which sets and hardens through a chemical reaction with water. Cement becomes one constituent of the finished concrete.

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Cement vs. Concrete at a Glance

Property	Cement	Concrete
What it is	A manufactured binder, usually supplied as a fine powder	A composite made with cement, water and aggregate
Main job	Forms a paste that binds particles together	Forms slabs, footings, walls, columns, pavements and precast units
Typical constituents	Portland cement is made primarily from ground clinker with gypsum and may include limestone; blended cements contain additional materials	Cement, water, fine and coarse aggregate; may also contain supplementary cementitious materials, admixtures, fibers or entrained air
How it is bought	In bags or delivered in bulk	As bagged concrete mix or ready-mixed concrete by volume
Why it hardens	Hydraulic cement reacts with water through hydration	Hydration hardens the paste that binds the aggregate

The American Concrete Institute defines concrete as a mixture of hydraulic cement, aggregates and water, with or without admixtures, fibers or other cementitious materials. It defines hydraulic cement by its ability to set and harden through hydration, including under water (ACI).

The distinction applies to purchasing as well as technical language. A bag labeled portland cement contains binder, not a complete concrete mixture. A bagged concrete mix generally contains the cementitious material and aggregates needed to make concrete, with water added according to the manufacturer’s directions.

Cement Paste Binds the Aggregate

When water contacts hydraulic cement, hydration begins. Cement paste surrounds the fine and coarse aggregate and gradually hardens into a solid mass.

Aggregate makes up most of concrete’s volume. The American Cement Association says cement commonly accounts for about 10% to 15% of a concrete mixture by volume, while aggregate commonly accounts for 60% to 75% (American Cement Association). The exact proportions depend on required strength, workability, exposure, aggregate grading and other project requirements.

This is why “add more cement” is not a complete concrete specification. Performance depends on the proportioning and quality of the whole mixture, along with placement, consolidation and curing. Too little paste can make concrete difficult to place and leave rough, porous work. Excess paste adds cost and can increase susceptibility to cracking (American Cement Association).

Concrete also does not simply dry into its final state. Hydration consumes water chemically. Curing controls moisture and temperature so hydration and strength development can continue. Allowing exposed concrete to lose moisture too quickly interferes with that process; adding unapproved water during mixing or placement changes the mixture instead of curing it.

Concrete, Mortar and Grout Serve Different Jobs

Concrete, mortar and grout can all contain hydraulic cement, but their aggregate and consistency are selected for different work.

• Concrete normally contains fine and coarse aggregate. It is used for structural and nonstructural elements such as slabs, walls and footings.
• Mortar combines cement paste with fine aggregate and is formulated to bed and bond masonry units. It normally contains no coarse stone. A cement-based repair mortar must also be selected for its permitted thickness, orientation and exposure rather than treated as ordinary concrete.
• Grout is a fluid mixture of cementitious materials and water, with or without fine aggregate. In a concrete blockwork wall, masonry grout fills specified cells and surrounds reinforcement; it is not simply ordinary concrete with the coarse stone removed.

Substituting one for another because each contains cement can produce the wrong flow, bond, shrinkage or placement characteristics for the detail. Concrete designed to hold coarse aggregate in suspension is not automatically suitable for filling narrow masonry cells. Mortar designed for masonry joints is not a substitute for structural concrete.

“Cement” is also not a general name for every gray bag on the pallet. Mortar, grout, stucco, concrete and repair products may look similar before water is added, but their formulations and permitted uses differ. The product name and current data sheet—not color or texture—determine where a bagged mix belongs.

Order Concrete for Slabs, Footings and Walls

For a ready-mix slab, footing or wall, order concrete by volume and give the supplier the requirements from the drawings and specifications. Depending on the project, those requirements may include compressive strength, exposure requirements, slump, air content, maximum aggregate size and placement method.

Do not replace the specified mixture with a crew-devised cement-and-aggregate ratio. Project requirements can control durability, workability and compatibility with reinforcement or placement equipment, not only compressive strength.

Delivery capacity is a separate issue from mixture selection. Use how much concrete a truck holds to plan loads and trips after confirming the required concrete volume and the supplier’s delivery constraints.

For small site-mixed work, read the complete bag label:

• Portland cement is binder. Aggregate and water must still be proportioned correctly to make concrete.
• Concrete mix is generally a preblended product containing cementitious material, sand and coarse aggregate. Add water only as directed by the manufacturer.
• Mortar, grout, stucco and repair mixes are application-specific. Check the current product data sheet for permitted thickness, yield, water addition, working time and substrate preparation.

Do not add water by eye simply to make a mixture easier to place. Increasing mixing water changes the water-cement ratio and can reduce strength and durability. Follow the approved mixture requirements or the bag manufacturer’s instructions.

Wet Concrete Still Presents Cement Hazards

Cement does not stop being hazardous after it is combined with aggregate and water. Wet concrete, mortar and grout expose workers to the cement they contain.

OSHA warns that wet portland cement is caustic, abrasive and moisture-absorbing. Skin contact can cause dermatitis or chemical burns, and a cement burn may not cause immediate pain (OSHA). That delayed pain makes prompt washing and proper protective equipment particularly important when material gets inside gloves, boots or clothing.

Use the controls and PPE required by the hazard assessment and product safety data sheet. OSHA’s guidance addresses minimizing skin contact, suitable gloves and boots, protective clothing, eye protection and accessible washing facilities. Dry cement handling also requires control of airborne dust.

On purchase orders, mix tickets, submittals and crew instructions, use the precise material name: cement binds; concrete builds.