NICET CMT Concrete key terms

The mass of water in a mixture divided by the total mass of cement and supplementary cementitious materials. Lower ratios generally raise strength and reduce permeability but make concrete harder to place.

Materials such as fly ash, slag cement, or silica fume that are blended with portland cement or added at the mixer, reacting to contribute strength and durability while reducing the cement content.

A fine powdery byproduct of coal-fired power plants used as a pozzolan. It improves workability and long-term durability, lowers heat of hydration, and usually slows early strength gain.

A glassy iron-manufacturing byproduct ground to cement fineness and used as a cementitious component. It improves sulfate resistance and lowers permeability, but can slow early strength in cool weather.

An extremely fine byproduct of silicon and ferrosilicon production. Used at small dosages, it greatly increases strength and reduces permeability, but raises water demand and typically requires a high-range water reducer.

Deliberate introduction of microscopic air bubbles with an admixture to improve resistance to freezing and thawing and to deicing chemicals. The amount is measured as air content in the fresh concrete.

A material other than cement, water, and aggregate added to a batch to change fresh or hardened properties, such as water reduction, air entrainment, retardation, acceleration, or corrosion inhibition.

The distribution of particle sizes in an aggregate, expressed as percent passing each sieve. Gradation affects workability, water demand, void content, and the amount of cement paste needed.

A batch made in a laboratory or plant to confirm that proposed mixture proportions produce the required slump, air content, strength, and durability before production begins.

A reaction between alkalis in the pore solution and reactive silica in some aggregates that forms a swelling gel, causing map cracking and expansion. Low-alkali cement or suitable SCMs can mitigate it.

Collecting a representative portion of fresh concrete for testing, commonly per ASTM C172 from a stationary mixer or after discharging part of a truck load, and protecting it from evaporation.

A field measure of fresh concrete consistency per ASTM C143. Concrete is placed in a standard cone in three layers, rodded, struck off, and the drop after removing the cone is recorded.

A field test per ASTM C231 in which a known volume of concrete is pressurized and the resulting volume change is read as air content. It is not suitable for very porous aggregates.

A field method per ASTM C173 that determines air content by agitating concrete in a water-filled meter and reading the displaced water. It is useful for lightweight or porous aggregates.

The temperature of fresh concrete, measured to the nearest degree with a calibrated thermometer at least 75 mm into the sample per ASTM C1064. Limits protect against cracking and slow strength gain.

The mass of fresh concrete per unit volume, determined per ASTM C138 by filling, consolidating, and weighing a standard measure. It is used to compute yield and check batch consistency.

Removing entrapped air from fresh concrete by rodding, tamping, or vibration in layers. Adequate consolidation is needed for representative test specimens and dense, durable in-place concrete.

A watertight, rigid cylindrical container used to cast compressive strength specimens, commonly 100 by 200 mm or 150 by 300 mm. It must hold the specified dimensions and not absorb water.

Preparing the ends of a hardened cylinder so they are flat, parallel, and perpendicular to the axis, using sulfur mortar, cement paste, grinding, or neoprene pads, to ensure uniform load application.

A cap formed by pouring molten sulfur-based compound onto a cylinder end and letting it harden. It must meet thickness and strength requirements and be allowed to cure before testing.

A resilient bearing pad used with a retaining ring to cap concrete cylinders within specified strength and size limits. Pads must be checked for wear, flatness, and proper hardness.

Storing test cylinders in a moist room or water tank at 23 plus or minus 2 degrees Celsius from demolding until testing, unless the specification requires field curing for a particular purpose.

A cylinder cured at the project site near the concrete it represents, used to estimate in-place strength for form removal, post-tensioning, or opening to traffic rather than for acceptance.

Breaking a standard cylinder in axial compression per ASTM C39 and dividing the maximum load by the cross-sectional area to report stress in psi or MPa.

Specified rules that decide whether concrete conforms, typically based on averages of strength tests and the allowable difference between individual tests, as in ACI 318.

The average compressive strength of two cylinders made from the same sample and tested at the specified age. This average is the value compared with acceptance criteria.

A defined quantity of concrete evaluated as a unit for acceptance, often one day's placement of a given mixture or a specified volume, from which required samples are taken.

Drilling and testing a core from hardened concrete per ASTM C42 when cylinder results are low or questionable. Core strength is adjusted for length-to-diameter ratio and moisture condition.

A documented failure to meet a specification requirement, such as low strength or air content outside tolerance. It triggers evaluation, notification, and possible corrective action or acceptance by investigation.

Checking forms, reinforcement, embedments, and subgrade before concrete is placed to confirm they match approved drawings and specifications and are ready to receive concrete.

A record showing who collected, transported, stored, and tested a sample and when, demonstrating that specimens remained identifiable and were not altered before testing.

A written record of sample identification, test method, results, and deviations, signed by the tester. It is the formal evidence used for acceptance decisions and project records.

Comparing a test instrument or machine with a traceable reference standard to establish its accuracy, performed on a required schedule and documented for the equipment record.

Gear such as safety glasses, gloves, boots, and a hard hat worn during sampling and testing to protect against concrete burns, silica dust, and physical hazards.

Fine quartz dust released when concrete is cut, ground, or drilled. Inhalation can cause silicosis, so wet methods, ventilation, and respiratory protection are required.

A standardized document listing a product's hazards, safe handling, first aid, and spill response, required for chemicals such as admixtures, curing compounds, and form release agents.

A chemical burn from prolonged skin contact with wet concrete, which is highly alkaline. It may be painless at first but can be severe; wash immediately and seek medical attention.