ACI CLTT-2 key terms

A procedure that shakes a dried aggregate sample through a stacked series of woven-wire sieves and records the mass retained on each sieve, producing the particle-size distribution used to judge gradation.

The distribution of particle sizes within an aggregate sample, described by the percentages passing each sieve in a sieve analysis and used to judge whether the material is well or poorly graded.

The smallest sieve opening through which the entire aggregate sample passes, or the largest sieve retaining any material, depending on the defining specification; it guides minimum specimen dimensions and mix proportions.

A single number obtained by adding the cumulative percentages retained on a specified set of sieves and dividing by 100; it indicates the average coarseness of a fine aggregate.

The mass of an aggregate sample after drying to constant mass at a specified temperature, usually about 110 degrees Celsius, used as the reference condition for moisture and absorption calculations.

A state in which the aggregate's permeable pores are filled with water while the particle surfaces remain dry, achieved by removing free surface moisture; it is the reference basis for absorption and bulk specific gravity.

The increase in mass of an aggregate after soaking in water, expressed as a percentage of its oven-dry mass; it reflects the pore volume that can take in water and influences effective water in a mix.

The mass of water present in an aggregate expressed as a percentage of its oven-dry or as-received mass, determined by drying and used to adjust batch water quantities.

The ratio of an aggregate's oven-dry mass to the mass of water displaced by the particle volume including its permeable pores, used to convert between mass and absolute volume in mix design.

The ratio of an aggregate's oven-dry mass to the mass of water displaced by the solid volume only, excluding permeable pores, giving a value higher than bulk specific gravity.

The proportion of fine material passing a small sieve, such as the 75-micrometer sieve, in a coarse or fine aggregate; excessive dust can raise water demand and affect bond.

A test procedure in which an aggregate sample is agitated in water over a fine sieve to separate and remove material finer than the sieve, quantifying the dust or fines content.

Soft or degradable particles in aggregate that break down when wet-sieved, determined by soaking and washing a sample and expressing the loss as a percentage of the original mass.

Aggregate particles with a specific gravity below a specified threshold, separated by flotation in a heavy liquid and reported as a percentage; they can lower concrete strength and durability.

A colorimetric screening test in which aggregate is soaked in a sodium hydroxide solution and the resulting color is compared with a reference standard to flag potentially harmful organic matter.

A confirmatory procedure that compares compressive strength of mortar cubes made with the suspect fine aggregate against cubes made with a known good sand, used when organic impurity results are inconclusive.

An aggregate's resistance to volume change and disintegration when subjected to repeated wetting and drying or freezing and thawing, often assessed by immersion cycles in saturated salt solutions.

An aggregate's ability to resist wear and breakdown under mechanical action, measured by tumbling a graded sample with steel spheres in a rotating drum and reporting the percentage lost.

A toughness index found by subjecting a prepared aggregate sample to repeated hammer blows and reporting the percentage of material passing a specified sieve after the impact.

The percentage by mass of aggregate particles whose least dimension is less than a specified fraction of their nominal size, indicating flat or elongated shapes that can impair workability and packing.

The percentage by mass of aggregate particles whose greatest dimension exceeds a specified multiple of their nominal size, used with the flakiness index to describe particle shape.

The geometric form of aggregate particles, described as rounded, angular, flaky, or elongated; it affects workability, packing density, and interlock in a concrete mixture.

The process of obtaining a representative portion of an aggregate lot using prescribed methods and reduction techniques so that test results fairly describe the whole material.

A manual sample-reduction method in which a flattened pile of aggregate is divided into four equal parts and opposite quarters are retained until a test-sized portion remains.

Any accepted procedure, such as quartering or a mechanical splitter, that reduces a large field sample to a smaller portion still representative of the original material.

A workability test in which freshly mixed concrete placed in a standard cone is consolidated and the cone removed; the vertical drop of the settled mass is measured as slump.

The ease with which fresh concrete can be mixed, placed, consolidated, and finished without segregation, judged by tests such as slump, flow, or compaction factor.

The process of removing entrapped air from fresh concrete by rodding, vibration, or tamping so the material fills the mold or form and reaches its intended density.

The separation of coarse aggregate from mortar or paste in fresh concrete, often caused by over-wetting, excessive handling, or dropping from height, leading to nonuniform hardened properties.

The upward migration of mixing water to the surface of freshly placed concrete as solids settle, which can raise the water-cement ratio near the top and weaken that zone.

The volume percentage of air voids in a concrete mixture, measured by pressure, volumetric, or gravimetric methods and important for freeze-thaw resistance of hardened concrete.

Maintaining adequate moisture and temperature in concrete after placement so cement hydration can continue, which develops strength, durability, and reduces early shrinkage cracking.

The maximum stress a hardened concrete specimen sustains under axial compression, usually measured on cylinders or cubes at a specified age and reported as force per unit area.

Applying a thin layer of suitable material to the ends of a compression specimen to make them flat, parallel, and perpendicular to the axis so load is applied uniformly.

A cylindrical test specimen of fresh or hardened concrete, commonly cast in a mold of specified diameter and length, used for strength and other hardened-property tests.

A statistical measure of test result scatter, calculated as the standard deviation divided by the mean and expressed as a percentage, used to judge testing and production consistency.

A statistical measure of how widely individual test results spread around their average value; it is used with the mean to evaluate concrete strength variability and acceptance criteria.

The ability of hardened concrete to resist deterioration from repeated cycles of freezing and thawing, strongly influenced by entrained air content, water-cement ratio, and curing.