ACI CTCI key terms

A field procedure that measures how far a molded cone of fresh concrete settles after the mold is lifted, indicating consistency and workability of the mix.

The standard metal mold, open at both ends, used to form the fresh concrete specimen for the slump test; its dimensions and smooth interior are specified by test method.

The ease with which fresh concrete can be mixed, placed, consolidated, and finished without segregation, judged from consistency and cohesion rather than a single measured property.

The relative mobility or stiffness of fresh concrete, commonly described as wet, plastic, or stiff and typically assessed in the field by the slump test.

The separation of coarse aggregate from the mortar or paste in fresh concrete, often caused by over-vibration, excessive water, or dropping the mix from too great a height.

The upward migration of mixing water to the surface of freshly placed concrete as solid particles settle, which can weaken the top layer and cause laitance.

A weak, dusty layer of fine cementitious material and water that collects on the surface of fresh or hardened concrete, reducing bond and surface durability.

The intentional introduction of tiny, evenly distributed air bubbles into concrete, usually with an admixture, to improve resistance to freezing and thawing and deicer scaling.

A field or laboratory procedure, such as the pressure or volumetric method, that determines the percentage of entrained and entrapped air in a fresh concrete sample.

A material other than cement, water, and aggregate added to a concrete batch, before or during mixing, to modify fresh or hardened properties such as set time or durability.

An admixture that lowers the water demand of a mix for a given consistency, or increases slump without added water, by dispersing cement particles.

An admixture that slows the chemical hydration reaction, extending workable time and delaying initial set, useful in hot weather or long hauls.

The chemical reaction between cement compounds and water that forms hydration products, generates heat, and causes concrete to set and gain strength over time.

The point in the setting process at which fresh concrete begins to stiffen and loses its ability to be remixed or reworked without adding water or disturbing the mix.

A laboratory procedure using a penetrometer on a sieved mortar sample to determine initial and final setting times of a cementitious mixture under controlled conditions.

The mass of water divided by the total mass of cement and other cementitious materials in a mix, a key factor controlling strength, permeability, and durability.

The process of selecting proportions of cementitious materials, water, aggregate, and admixtures to produce concrete with specified strength, durability, and workability.

A test mixture prepared and tested before production to confirm that proposed proportions achieve the required fresh and hardened properties.

A standard molded cylindrical concrete sample, cast and cured under prescribed conditions, used to determine compressive strength in the laboratory.

The process of forming smooth, parallel ends on a hardened concrete cylinder, using a suitable material, so that load is applied uniformly during compressive strength testing.

A laboratory test in which a hardened concrete specimen is loaded axially until failure to determine the maximum stress it can carry, typically reported in pressure units.

Field slang for the result of a destructive strength test on a concrete specimen, commonly the compressive strength measured at a specified age.

Maintaining adequate moisture and temperature in concrete after placement so that hydration can continue and the intended strength and durability develop.

A liquid applied to the surface of fresh or recently finished concrete that forms a membrane to reduce moisture loss during the curing period.

The process of removing entrapped air and compacting fresh concrete into forms and around reinforcement, usually by vibration, to eliminate voids and honeycomb.

A mechanical device, typically internal or poker type, inserted into fresh concrete to consolidate it by transmitting high-frequency oscillations that fluidize the mix.

Voids or cavities left in concrete where mortar failed to fill the spaces between coarse aggregate particles, often from inadequate consolidation or blockage by reinforcement.

The temporary molds, supports, and bracing that hold fresh concrete in the required shape and position until it hardens sufficiently to be self-supporting.

The temporary structural supports, such as shoring and scaffolding, that carry the weight of formwork and fresh concrete during construction.

A coating applied to form surfaces to prevent concrete from bonding to the formwork, allowing clean removal without surface damage.

The thickness of concrete between the outer surface of embedded reinforcement and the nearest exposed concrete surface, protecting steel from corrosion and fire.

Steel reinforcing bars placed in concrete to carry tensile and shear forces, positioned per drawings and secured before concrete is placed.

A small device or block placed to hold reinforcement at the specified distance from the form surface, ensuring the required concrete cover is maintained.

A method of joining two reinforcing bars by overlapping their ends over a specified length so that force transfers from one bar to the other through bond.

A plane of weakness formed where fresh concrete is placed against concrete that has already stiffened or set, preventing a proper bond between the two layers.

A planned stopping place in concrete placement where work resumes later, detailed and prepared so the two sections act together structurally.

The mass per unit volume of fresh or hardened concrete, determined by weighing a known volume of material and used to check yield and density.

The volume of concrete actually produced per batch compared with the volume intended by the mix design, used to verify batching accuracy.

The thermal energy released as cement reacts with water, which can cause temperature rise and thermal cracking in large concrete placements.