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• Magnetite - 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.
• Marl - A calcareous clay, containing approximately 30 to 65 percent calcium carbonate (05003), found normally in extinct fresh wafer basins, swamps, or bottoms of shallow lakes.
• Masonry Cement - Hydraulic cement manufactured for use in mortars for masonry construction. Normally a blend of two or more of the following materials: portland cement, natural cement, portland-pozzolan cement, hydraulic lime, slag cement, hydrated lime, pulverized limestone, talc, chalk, pozzolan, clay or gypsum; also may include air en-training additions.
• Mass Concrete - Any large volume of concrete cast in place intended to resist applied loads by virtue of mass. Generally a monolithic structure incorporating a low cement factor with a high proportion of large coarse aggregate.
• Mass Curing - Adiabatic curing, using sealed containers.
• Maximum Size Aggregate - 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.
• Mixer - Equipment used for mixing or blending the materials used in the manufacture of concrete, grout or mortar.
• Mixing Speed - 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.
• Mixing Time - For stationary mixers, mixing time is calculated in minutes from the completion of charging the mixer until the beginning of discharge; for truck mixer, time is calculated in total minutes at a specified mixing speed. the period during which materials used in a batch of concrete are combined by the mixer.
• Modulus of Elasticity - A measure of the resistance of material to deformation. the ratio of normal stress corresponding strain for tensile or compressive stresses below the proportional limit of the material; elastic modulus is denoted by the symbol "2".
• Moist Room - 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.
• Monolithic - A plain or reinforced mass of concrete cast as a single, one piece, integral structure.
• Mortar - A mixture of cement, sand and water. When used in masonry construction, the mixture may contain masonry cement, or standard portland cement with lime or other ad-mixtures which may produce greater degrees of plasticity and/or durability.
• Neat Cement - Unhydrated hydraulic cement.
• Neat Cement-Paste - A mixture of water and hydraulic cement, both before and after setting and hardening.
• No-Fines Concrete - A concrete mixture in which only the coarse gradation (3/8' to 3/4' normally) of aggregate issued.
• Non-agitating Unit - A truck-mounted unit for transporting ready-mixed concrete short distances, not equipped to provide agitation (slow mixing) during delivery.
• Non-evaporable Water - The water in concrete which is irremovable by oven drying; chemically combined during cement hydration.
• Ottawa Sand - 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 - Excessive vibration of freshly mixed concrete during placement-causing segregation.

Contributions: Kaiser Cement, Portland Cement Association, Concrete Manual, Bureau of Reclamation, U. S. Department of the Interior and many other publications, with special thanks to Bob Cameron of W. R. Meadows. © 2008 Moxie International, Inc. All Rights Reserved.

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