| Neat Cement | (Concrete Engineering) Unhydrated hydraulic cement. |
| Neat Cement-Paste | (Concrete Engineering) A mixture of water and hydraulic cement, both before and after setting and hardening. |
| Non-agitating Unit | (Concrete Engineering) A truck-mounted unit for transporting ready-mixed concrete short distances, not equipped to provide agitation (slow mixing) during delivery. |
| Non-evaporable Water | (Concrete Engineering) The water in concrete which is irremovable by oven drying; chemically combined during cement hydration. |
| Ottawa Sand | (Concrete Engineering) A sand used as a standard in testing hydraulic cements by means of mortar test specimens. Sand is produced by processing silica rock particles obtained by hydraulic mining of the orthoquartzite situated in open-pit deposits near Ottawa, Illinois; naturally rounded grains of nearly pure quartz. |
| Overvibration | (Concrete Engineering) Excessive vibration of freshly mixed concrete during placement-causing segregation. |
| Particle-Size Distribution | (Concrete Engineering) Particle distribution of granular materials among various sizes; for concrete material normally designated as gradation. Usually expressed in terms of cumulative percentages smaller or larger than each of a series of sieve openings or percentages between certain ranges of sieve openings. |
| Peeling | (Concrete Engineering) A process in which thin flakes of matrix or mortar are broken away from concrete surface; caused by adherence of surface mortar-to forms as forms are removed, or to trowel or float in portland cement plaster. |
| Pining | (Concrete Engineering) Development of relatively small cavities in a concrete surface, due to phenomena such as cavitation or corrosion. |
| Plane of Weakness | (Concrete Engineering) The plane along which a structure under stress will tend to fracture; may exist because of the nature of the structure and its loading, by accident, or by design. |