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mortar, in building
mortar, in warfare
a smooth-bore gun for high-angle fire against concealed targets and for the destruction of field fortifications. The main combat characteristics of the mortar are the high power of the ammunition (mortar shell), high maximum rate of fire, relatively light weight, simplicity of design and combat application, and constant readiness to open fire without special preparation. The curvature of trajectory of the mortar shells (the angles of barrel elevation range from 45° to 85°) makes it possible to destroy protected targets that cannot be hit by rifles or machine guns or flat-trajectory artillery fire. Mortars are included in troop (in foreign armies, “field”) artillery.
Mortar shells were first fired successfully from an artillery gun by Russian troops during the defense of Port Arthur in the Russo-Japanese War of 1904–05. This experiment was imitated by other countries, and mortars of various calibers were developed. During World War I (1914–18) the most common mortars in the Russian Army were the 47-mm and 58-mm E. A. Likhonin mortars with a range of fire of 390 m and 510m, respectively, combat weight of 90 kg and 150 kg, and shell weight of 21 kg and 36 kg. In the late 1930’s, 50-mm, 82-mm, 107-mm, and 120-mm mortars were developed and adopted in the USSR;
|Table 1. Mortars used in various armies in World War II|
|Caliber(mm)||Combat weight(kg)||Shell weight(kg)||Range of fire(m)|
these guns were superior in combat characteristics to the foreign 50-mm, 81-mm, 105-mm, and 119-mm mortars. During World War II (1939–45) mortars were used extensively in all the combatant armies (see Table 1).
Mortars were used on a large scale in all the operations of the Soviet Army in the Great Patriotic War of 1941–45. Between 1941 and 1945, Soviet industry turned out 347,900 mortars; in Germany about 68,000 mortars were produced between 1941 and 1944. In the postwar years Soviet troops adopted improved high-power 160-mm and 240-mm mortars. Present-day mortars of various armed forces have calibers ranging from 81 mm to 240 mm, the mortar shells weigh between 3 kg and 130 kg, the maximum range of fire varies from 2,500 m to 10,000 m, and combat weights range from 35 kg to 3,600 kg. Mortars are divided into muzzle-loaders and breechloaders according to the method of loading. Small and medium caliber mortars (from 50 mm to 120 mm) are muzzle-loaded, whereas large ones (more than 120 mm) are loaded by the breech. Mortars are divided by barrel design into smooth-bore and rifled. Depending on the method of transportation, mortars may be carried (in a motor vehicle or armored personnel carrier), towed (in a trailer behind a prime Moler), self-propelled (on tracks or wheels), and packed (on draft animals in the mountains).
REFERENCELatukhin, A. N. Minomety. Moscow, 1970.
A. N. LATUKHIN
a construction material obtained from the hardening of specially selected mixtures of a binder with water (less often, without water) and a finely ground concrete aggregate. Depending on the use, mortars are divided into those used in masonry structures (primarily of brick and quarry stone), those used for plastering and the application of decorative layers on wall panels and blocks, and special mortars, such as water-insulating, acid-resistant, and acoustic mortars and mortars used to plug holes and cracks. A distinction is made between mortars with inorganic binders, such as cement, lime, gypsum, and mixtures thereof, for example, lime-cement, and mortars with organic binders, such as polymer and asphalt mortars.
Depending on the density, a distinction is made between heavy mortars (made with ordinary sand), with densities of 1,500 to 2,500 kg/m3, and lightweight mortars, with densities less than 1,500 kg/m3. To obtain lightweight mortars, finely ground, porous concrete aggregates are used, and the prepared binder mixed with water is made porous. Nine grades of mortars (grade 4 to grade 300) are distinguished on the basis of compressive strength (from 4 to 300 kg-force/cm2, or 0.4 to 30 meganewtons/m2).
The most common mortars are those made with mineral binders and used for masonry work and finishing. The general theory of such mortars was first developed in the USSR in the 1930’s by N. A. Popov. Analogous in composition to fine-aggregate or sand concretes, mortars differ from these concretes by their greater plasticity and, generally, lower strength; these properties dictate the specific use of mortars in the form of thin layers, which result from the setting of mortar mixtures on a porous base, such as brick or wood.
To obtain mortars of the required strength, the mortar mixture must have the required workability and water retentivity. The degree of workability is determined by the depth to which a standard metal cone, called a StroiTsNIL cone, sinks into the mortar. The water retentivity is the degree to which the mixed mortar resists separation into layers during transport and retains moisture while setting on a porous base, which is necessary for the normal hardening process. In order to reduce the amount of cement used in preparing low-grade mortars and to impart greater plasticity, low-strength but highly plastic binders, such as lime and clay, are added to the cement, finely ground additives, such as slags, ash from steam power plants, and sand, are introduced into the mortar, and surface-active plasticizer additives are used.
As a rule, mortars are prepared at special factories or mortar-mixing installations and then shipped to construction sites. Dry mortars, which are to be mixed with water before use, are also produced. At construction sites, mortar is distributed to various points by means of mortar pumps.
In modern construction, some mortars have a mixture of polymer and mineral binders, for example, polyvinyl acetate cement; these mortars adhere strongly to a base and are widely used, as are mortars having polymer binders and high chemical stability and strength and good decorative qualities. Such mortars are used mainly for floor coverings in public and industrial buildings.
REFERENCESStroitel’nye normy i pravila. Part 1, third section, ch. 2: Viazhushchie materialy neorganicheskie i dobavki dlia betonov i rastvorov. Moscow, 1969.
Ukazaniia po prigotovleniiu i primeneniiu stroitel’nykh rastvorov: SN 290–64. Moscow, 1965.
Vorob’ev, V. A., and A. G. Komar. Stroitel’nye materialy. Moscow, 1971.
K. N. POPOV
A binding agent used in construction of clay brick, concrete masonry, and natural stone masonry walls and, to much less extent, landscape pavements. Modern mortars are improved versions of the lime and sand mixtures historically used in building masonry walls. See Brick, Masonry
Masonry mortar is composed of one or more cementitious materials, such as masonry cement or portland cement and lime, clean sand, and sufficient water to produce a plastic, workable mixture.
Mortars are closely related to concrete but, like grout, generally do not contain coarse aggregate. Mortars function with the same calcium silicate-based chemistry as concrete and grouts, bonding with masonry units into a contiguous, weatherproof surface in the process. Masonry cement or portland cement-lime mortars can be formulated to address job-specific requirements including setting time, rate of hardening, water retentivity, and extended workability. See Cement, Concrete, Grout