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Mortar =mortar is as vital a part of masnory as the masnory units themselves. Mortar serves to Cushion the memory unit, giving them full bearing against one another despite their surface irregularities. Mortar seals between the units to keep water and wind from penetrating, it adheres the unit to one another to bond them into a monolithic structural unit, and inevitably, it is important to the appearance of the nished masnory wall. Mortar ingredients The most characteristic type of mortar is cement -line mortar, made of Portland cement, hydrated lime, an inter aggregate, and water. The aggregate and sand, must be clean and must be screened to eliminate particles that are too coarse or too NE, ASTM speci cation c144 eliminate started for mortar sand. The Portland cement is the bonding agent in the mortar .its composition and manufacture are described in more detail beginning on page 518 of this book. Only Portland cement, types 1,11,and 111 are recommended for use in masnory mortar. Mortar made only with Portland cement,however ,is harsh, meaning that it does not own well on the trowel or under the brick, so lime is added to impart smoothness and work ability. Lime is produced by burning limestone or seashells (calcium carbonate) in a kiln to drive off carbon dioxide and leave quicklime (calcium oxide). The quicklime is them slaked by allowing it to absorb as much water as it will hold, resulting in the formation of calcium hydroxide, called slaked lime or hydrated lime. The skating process, which release large quantities of heat, is usually carried out in the factory. The hydrated lime is subsequently dried, ground, and bagged for shipment. ASTM specication C207 governs the production of lime. Water is also an important ingredient in mortar because it is chemically involved in curing of the cement and lime. Water used in mortar should be clean and free of acids, alkalis and organic mater. Water that is potable is generally considered suitable for use in mortar. Blessed hydraulic cement, ASTM C595,are blends of Portland cement with other cementitionus materials, such as blast furnace slag, that may be used in place of ordinary Portland cement alone in the cement lime mortar mix. Masnory cement and mortar cement are prepackaged cement that do not require the addition of lime by the mason on the job site. Their main advantage are convenience, consistency (since the are premixed), and good work ability. Masonry cement are proprietary formulation that that may contain Portland cement or blended hydraulic cement, lime or other additives. Formulation vary from one manufacture to another, but all must comply with ASTM C91 . In order to achieve a work ability equipment to that of conventional cement lime mortar masonry cement mortar are formulated with air retraining admixture that that result in a higher air content in the cured mortar than cement lime mortar. This reduce the bond strength between the mortar and the masonry unit to about half that of conventional mortar, which means that the exural and shear strength of the wall is reduced and the wall is more permeable to water. For these reason, masnory cement should not be speci ed for masnory work that requires high strength and low permeability. Mortar cement are also blends of Portland cement, lime, and other additives. However, they are formulated according to ASTM C1329 ,with limits on air entrainmet that allow them to meet bond strength requirements comparable to those of cement lime mortar. Structural codes treat mortars made with mortar cement lime mortars.
Building materials and buildings are constantly in motion. Many of those motion are cyclical and never ending some are caused by temperatures changes .all materials shrink as they become warmer, each materials doing so at its own characteristic rate. And the table of coef client of thermal expansion in the appendix. Some are caused by chance in moisture content. Most porous material grow larger when wetted by water or humid air and smaller when they Dry out, also at another. These cyclical motions caused by temperatures and moisture can occur on a seasonal basis warm day cool nights, warm when the sun is shinning on a surface, cool when a cloud covers the sun. Some motion are caused by structural de ections under load, such as the slight sagging of beans, girders joists, and slabs. These motions can be very long term for dead loads and for oors supporting stored material in a warehouse. De ection can be medium term for snow on a roof and very short term for walls resisting gusting wind. Some motions are one time phenomena. Concrete and stuco shrink as they cure and dry out, whereas gypsum plaster expands upon curing. Clay brick expand slightly over time as they absorb atmoshorten slightly, and concrete beams and slabs sag a bit due to plastic creep of the material during the rst several year of a building life, then they stabilized. Posttensioned slabs and induced by the stretched steel tendons,soil compresses under the pressure of the foundation of a new building and then, in most cases, stops moving.
25 Feb, 2018
NIMS offers a diverse and vibrant community where students can not only excel academically but also grow personally through engaging experiences and supportive networks. Help other students by share your experiences at NIMS.