| Kelly Ball | (Concrete Engineering) A device for determining the consistency of fresh concrete. It is sometimes used as an alternative to the slump test. |
| Magnetite | (Concrete Engineering) An aggregate used in heavy weight concrete, consisting primarily of ferrous metaferrite (Fe304). A black magnetic iron ore with a specific gravity of approximately 5.2 and a Mohs hardness of about 6. |
| Mass Curing | (Concrete Engineering) Adiabatic curing, using sealed containers. |
| Maximum Size Aggregate | (Concrete Engineering) Aggregate whose largest particle size is present in sufficient quantity to affect the physical properties of concrete; generally designated by the sieve size on which the maximum amount permitted to be retained is 5 or 10 percent by weight. |
| Mixing Speed | (Concrete Engineering) Rate of mixer drum rotation or that of the paddles in a pan, open-top, or trough type mixer, when mixing a batch; expressed in revolutions per minute (rpm) or in peripheral] feet per minute of A point on the circumference at maximum diameter. |
| Moist Room | (Concrete Engineering) A room used for storing and curing cementitious test specimens. The atmosphere of this room is maintained at a temperature of 73.4 3.0'F or 23.0*1.7'0 and relative humidity of at least 98 percent. These facilities must be adequate to continually maintain free moisture on the exteriors of test specimens. |
| 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. |