Engineer Concrete key terms

Mass of water divided by total mass of cement plus supplementary cementitious materials in a mixture. Lower values generally raise strength, reduce permeability, and improve durability; it is the single most influential mix parameter.

Materials such as fly ash, slag cement, silica fume, and natural pozzolans that partially replace portland cement. They react pozzolanically or hydraulically, slow early strength gain, reduce heat, and refine pore structure.

Chemical reaction in which amorphous silica or alumina combines with calcium hydroxide in the presence of moisture to form additional calcium silicate hydrate. It consumes free lime and densifies the paste, improving long-term strength and impermeability.

The principal binding phase formed when cement hydrates. It is a poorly crystalline gel that coats particles, fills space, and provides most of the strength and dimensional stability of hardened paste.

Interconnected void space left in hardened paste where water was not consumed by hydration. It controls permeability, transport of aggressive ions, and freeze-thaw vulnerability; it shrinks as the water-cementitious materials ratio decreases and curing continues.

Distribution of aggregate particle sizes expressed as percent passing a series of standard sieves. Well-graded blends reduce paste demand and void content, while gap-graded or poorly graded blends can cause harshness or segregation.

An index computed from cumulative percentages retained on a set of standard sieves, divided by 100. It summarizes how coarse or fine an aggregate is and helps detect batch-to-batch grading shifts.

The largest standard sieve through which most of a coarse aggregate passes, used for mix proportioning and clearance checks. Larger sizes reduce paste demand but are limited by member dimensions, reinforcement spacing, and placing method.

A material other than cement, water, or aggregate added to a batch to modify fresh or hardened properties. Common types include water reducers, retarders, accelerators, air entrainers, and corrosion inhibitors.

A standard measure of fresh concrete consistency obtained by filling a cone, removing it vertically, and measuring the drop of the settled mass. It indicates workability trends but is insensitive to cohesion and segregation resistance.

The spread diameter of a slumped cone of fresh concrete, used to characterize highly flowable self-consolidating mixtures. It reflects flowability and, with the T50 time, filling ability and viscosity.

Separation of coarse aggregate from mortar or paste during handling, placing, or vibration. It produces nonuniform strength and permeability, and is controlled by cohesive mix design and proper placement procedures.

Upward migration of mixing water to the concrete surface as solids settle before setting. Excessive bleeding creates weak laitance layers, plastic settlement cracks, and poor bond between lifts or at the top surface.

A weak, dusty layer of cement fines and water deposited at the top of a concrete lift or slab. It must be removed before placing subsequent concrete or applying a bonded finish, because it prevents bond.

Compaction of fresh concrete by internal or external vibration to remove entrapped air and ensure the paste fills formwork and surrounds reinforcement. Inadequate consolidation leaves honeycomb and voids that reduce strength and durability.

Voids and exposed coarse aggregate left in a concrete surface where mortar failed to fill the space. It results from inadequate consolidation, congested reinforcement, or stiff, poorly placed mixtures.

A highly flowable, cohesive mixture that spreads under its own weight, fills formwork, and passes through reinforcement without vibration. It relies on high paste content, viscosity-modifying admixtures, and careful aggregate control.

Maintaining adequate moisture and temperature in young concrete so hydration can continue. Proper curing improves strength, reduces permeability, and limits plastic shrinkage and surface defects; its duration depends on mixture and exposure.

The speed at which surface water leaves fresh concrete, driven by air temperature, wind, relative humidity, and concrete temperature. High rates cause rapid surface drying and plastic shrinkage cracking before the concrete can resist tension.

Cracks that form on a fresh concrete surface when water evaporates faster than bleed water can replace it. The surface shrinks while the interior restrains it, producing short parallel or map cracks.

Cracking caused by differential cooling in thick elements where heat of hydration raises interior temperature. The cooler surface contracts against the warmer core, generating tensile stress that can exceed early-age strength.

Heat released as cement compounds react with water. In massive sections it can produce large temperature gradients and thermal cracking, so it is managed through low-heat cement, SCMs, and temperature control.

The maximum stress a concrete specimen sustains in compression, typically measured on standard cylinders or cubes at a specified age. It is the primary acceptance property and the basis for structural design strength.

The slope of the stress-strain curve in compression, reflecting stiffness and resistance to deformation. It depends mainly on strength and aggregate stiffness and governs deflections and second-order effects in structures.

Time-dependent deformation of concrete under sustained stress, beyond immediate elastic strain. It increases deflections, relaxes prestress, and is influenced by load level, age at loading, humidity, and mixture proportions.

Volume reduction as moisture leaves hardened concrete, causing shortening and warping of elements. Restraint of shrinkage by reinforcement or supports produces tensile stress and potential cracking.

Extraction and compression testing of drilled concrete cores to estimate in-place strength. Results are adjusted for core diameter, length-to-diameter ratio, moisture condition, and drilling damage, and are used in forensic and acceptance disputes.

A nondestructive method in which a spring-driven mass strikes the concrete surface and rebound distance indicates hardness. It gives a quick relative indication of uniformity and strength but requires correlation with cores.

Proportioning of a prestressed member so that prestress and applied loads produce compatible stress distributions, often with no tension at service. It considers allowable stresses at transfer and at service and the resulting camber.

The stage when prestressing force is applied to the concrete, either by releasing strands in pretensioning or by jacking and anchoring tendons in post-tensioning. Concrete strength at transfer must be adequate to resist the induced stresses.

Reduction of the initial prestressing force over time due to elastic shortening, creep, shrinkage, and steel relaxation, plus friction and anchorage losses in post-tensioning. Losses must be estimated to ensure adequate service behavior.

The ease with which chloride ions move through concrete, often assessed by rapid chloride permeability testing. High permeability allows chlorides to reach reinforcement and initiate corrosion, especially in marine or deicing exposures.

The chloride concentration at the steel surface at which the passive film breaks down and corrosion begins. It depends on pH, moisture, and steel condition, and is used to judge corrosion risk in service-life models.

Reaction of atmospheric carbon dioxide with calcium hydroxide in concrete, lowering pH and destroying the passive film around steel. Carbonation depth grows with time and is faster in dry, permeable, uncracked concrete.

Expansion caused by reaction between alkali pore solution and reactive silica in aggregate, producing gel that absorbs water and cracks concrete. It is mitigated by low-alkali cement, SCMs, and nonreactive aggregates.

The distance from the concrete surface to the nearest reinforcement. Adequate cover protects steel from chlorides and carbonation, provides fire resistance, and must be verified during inspection.

Sampling and testing of fresh or hardened concrete from production batches to verify compliance with specification requirements. Proper sampling frequency, handling, and curing of specimens are essential for valid results.

Verification before concrete is placed that formwork, reinforcement, embedments, and subgrade meet drawings and specifications. It includes checking dimensions, cover, cleanliness, and stability of forms and supports.

Microscopic study of hardened concrete thin sections or polished surfaces to identify aggregate, paste, cracks, and deterioration mechanisms. It supports forensic diagnosis of ASR, freeze-thaw damage, and improper mixing.

A shallow, conical depression at a concrete surface caused by expansion of a near-surface particle or by freeze-thaw action on porous aggregate. It is a cosmetic surface defect but can indicate durability problems.