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Concrete Repair Terminology (N-O)
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Concrete Repair Terminology is prepared by the International Concrete Repair Institute. The cross-referenced terms provide definitions for commonly used words in concrete repair, restoration and protection.

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Revised April 2019

A   |   B   |   C   |   D   |   E   |   F   |   G   |   H   |   I   |   J-L   |   M   |   N-O   |   P   |   Q-R   |   S   |   T   |   U-V   |   W   |   X-Y-Z

- N -

natural frequency

natural frequency—the frequency at which a system that has been moved from its resting position will oscillate about the position if there are no disturbing forces.

neat cement grout

neat cement paste


the change in cross-sectional area of a material as it elongates.

needle scaling

a surface preparation method in which the surface is impacted with the pointed tips of a bundle of steel rods contained by a steel tube and pulsed by compressed air.

negative side waterproofing

applying waterproofing to the side of a structural element opposite the one subjected to hydrostatic pressure.


an elastomer, polychloroprene, formed by adding hydrogen chloride to monovinylacetylene.


in electrical systems, the term used to indicate neither an excess nor a lack of electrons; a condition of balance between positive and negative charges. In chemistry, the term used to indicate a balance between acids and bases; the neutral point on the pH scale is 7.0, indicating the presence of equal numbers of free hydrogen (acidic) and hydroxide (basic) ions.

noble metal

a metal with a standard electrode potential that is more noble (positive) than that of hydrogen.

nondestructive testing(NDT)

examination of materials and structures in ways that do not impair future usefulness and serviceability in order to detect, locate, and measure discontinuities, defects, and other imperfections to assess integrity, properties, and uniformity, and to measure geometrical characteristics.

nondestructive evaluation (NDE)

condition evaluation conducted with nondestructive methods.

non-evaporable water

the water that is chemically combined during cement hydration; not removable by specified drying. (See also evaporable water.)


an open-ended metal or rubber tip attached to the discharge end of a shotcrete nozzle body.

nozzle body

a device at the end of a shotcrete delivery hose that contains a regulating valve and a manifold for adding water or air to the shotcrete mixture.

nozzle liner

a rubber lining placed inside the nozzle tip to provide abrasion protection.

nozzle operator

the technician who manipulates the nozzle and controls placement of the shotcrete; in the case of dry-mix shotcrete, the technician also controls the water content of the shotcrete.

nozzle velocity

the velocity (speed) at which shotcrete is ejected from the nozzle.

- O -

objectives of the remedial Work

restore, maintain, or enhance the performance level of the existing structure for its intended use and life expectancy, which for the design requires specific design criteria and implementing remedial Work.


the ability of a surface-applied coating to obliterate or hide the color of the surface to which it is applied.

open-circuit grouting

open-circuit potential

the potential of an electrode measured with respect to a reference electrode or another electrode when no current flows to or from it.

orange peel

the dimpled appearance of a dried surface-applied coating that resembles the peel of an orange.


spontaneous flow of water from a less concentrated solution to a more concentrated solution through a semipermeable membrane until chemical potential equilibrium is achieved.; the tendency of fluids to diffuse in such a manner.

osmotic pressure

the pressure required to maintain an equilibrium, with no net movement of fluid through a semipermeable membrane.


the upward and outward emission of air or moisture vapor from concrete or mortar.


the quantity of material that is excavated or breaks out beyond the perimeter of a specific removal area.


a bonded or unbonded layer of material placed on a concrete surface to either restore or improve the function of the previous surface.

overlay, bonded

increase in section of an existing concrete element by addition of a layer of material in direct contact with and adhering to the existing concrete surface.

overlay, unbonded

increase in section of an existing concrete element by addition of a layer of material placed on a separator layer (bond breaker) designed to prevent bonding to the existing concrete.


1) in protective coatings, any material not deposited within the surface area specified for coating. 2) in shotcreting, material deposited away from the intended receiving surface.


(See ACI 562 for code specific language.)


loss of electrons by a constituent of a chemical reaction; also refers to the corrosion of a metal that is exposed to an oxidizing gas.


to unite with oxygen; cause the oxidation of; rust.

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