ACI CQTM key terms

The mass of water divided by the total mass of cement plus supplementary cementitious materials in a mixture. Lower values generally increase strength, reduce permeability, and improve durability.

Materials such as fly ash, slag cement, silica fume, or natural pozzolans used in concrete in addition to portland cement. They can improve workability, reduce permeability, and slow early strength gain.

The chemical reaction between cement compounds and water that forms hydration products and causes concrete to set and harden. It generates heat and requires available moisture to continue.

The heat released as cement reacts with water. In thick sections it can raise internal temperature enough to cause cracking or delayed ettringite formation if not controlled.

A siliceous or siliceous-aluminous material that, alone, has little cementitious value but reacts with calcium hydroxide in moist conditions to form compounds with cementitious properties.

The process of selecting proportions of cementitious materials, water, aggregate, and admixtures to achieve required strength, durability, and workability at the lowest reasonable cost.

A measure of fresh concrete consistency obtained by filling a standard cone, removing it, and measuring the vertical drop of the settled concrete. Higher slump indicates a wetter mixture.

A test for highly flowable or self-consolidating concrete in which the spread diameter of concrete is measured after a slump cone is lifted. It indicates flowability and filling ability.

The ease with which fresh concrete can be mixed, placed, consolidated, and finished without segregation or loss of uniformity. It depends on water content, aggregate grading, and admixtures.

Separation of the constituents of fresh concrete so that the mix is no longer uniform. It commonly appears as coarse aggregate settling or paste and water rising to the surface.

The migration of mixing water to the surface of freshly placed concrete as solid particles settle. Excessive bleeding can weaken the top layer and reduce bond with subsequent placements.

The process of removing entrapped air from freshly placed concrete, usually by vibration, so it fully surrounds reinforcement and fills the form. Proper consolidation reduces voids and honeycomb.

Mechanical agitation of fresh concrete using internal or external vibrators to compact it into forms and around embedded items. Overvibration can cause segregation; undervibration leaves voids.

Voids or cavities in concrete where mortar has failed to fill the space among coarse aggregate particles. It typically results from inadequate consolidation or grout loss from forms.

Maintaining adequate moisture and temperature in concrete during early hardening so hydration can continue. Proper curing improves strength, durability, and reduces shrinkage and surface defects.

A liquid applied to a concrete surface that forms a membrane to limit moisture evaporation during curing. Application rate and coverage must meet specification requirements.

Loss of water from the surface of fresh concrete to the air. Rapid evaporation can cause plastic shrinkage cracking before the concrete has gained strength.

Cracks that form in the surface of fresh concrete when water evaporates faster than bleed water rises to replace it. They typically appear shortly after placement in hot, dry, or windy conditions.

A material other than cementitious materials, water, or aggregate added to a concrete batch to modify properties such as setting time, workability, air content, or durability.

An admixture that creates tiny, stable air bubbles in concrete to improve resistance to freezing and thawing and to deicing salts. Air content is verified by testing fresh concrete.

The volume percentage of air voids in fresh or hardened concrete. It is measured to confirm entrained air for freeze-thaw durability and to detect unintended air.

An admixture that slows the setting time of concrete, useful in hot weather or long hauls. Overdosing can delay finishing and formwork removal.

An admixture that speeds up setting and early strength gain, often used in cold weather. Some accelerators containing chlorides can promote corrosion of embedded steel.

The time required for fresh concrete to reach initial and final set. It is measured with penetration resistance tests and affects finishing, sawing, and formwork removal schedules.

The ability of concrete to resist weathering, chemical attack, abrasion, and other deterioration while maintaining its intended service function over its design life.

The ease with which fluids can pass through concrete. Low permeability limits water and aggressive ion movement, improving resistance to deterioration and protecting embedded reinforcement.

The ability of concrete to withstand repeated cycles of freezing and thawing without cracking or scaling. It is improved by entrained air, low permeability, and adequate strength.

Electrochemical deterioration of embedded steel reinforcement, often initiated by chloride ingress or carbonation. Corrosion products expand and can crack or spall the surrounding concrete.

The distance from the outer concrete surface to the nearest surface of embedded reinforcement. Adequate cover protects steel from moisture, chlorides, and fire damage.

Temporary molds and supports that hold fresh concrete in the required shape and position until it can stand alone. Formwork must be tight, stable, and properly released.

A material applied to form surfaces to prevent fresh concrete from bonding to the form. Proper application eases stripping and protects the concrete surface finish.

The maximum load a concrete specimen can carry per unit area when compressed, typically measured on cylinders or cubes at specified ages. It is the primary basis for structural acceptance.

The compressive strength of concrete required by the project specifications, usually stated at 28 days. It is used in structural design and acceptance criteria.

A standard molded or drilled cylindrical concrete specimen used for compressive strength testing. Molding, curing, and capping must follow standardized procedures to yield valid results.

The increase in concrete strength over time as cementitious materials continue to hydrate. Most strength develops in the first 28 days, but slow-reacting SCMs gain strength later.

The rules in a specification that determine whether concrete or construction work conforms to requirements. They define sampling frequency, test methods, and limits for acceptance or rejection.

The contractor's planned activities and tests used to verify that materials and workmanship meet specified requirements during production and construction.

The owner's or independent party's oversight activities that confirm the quality system is functioning and that constructed work complies with the contract documents.

Visual and measured examination of materials, reinforcement, forms, and finished concrete to verify compliance with plans and specifications before, during, and after placement.