房建外文翻译--建筑材料—混凝土与砂浆-建筑结构(编辑修改稿)

房建外文翻译--建筑材料—混凝土与砂浆-建筑结构(编辑修改稿)内容摘要：

terial. If the proportions of water, cement, and aggregate are carefully calculated and if the concrete is placed and allowed to cure according to simple but definite rules, it is possible to obtain from the concrete all the strength and durability that is inherent in it. The ratio of water to cement in a batch of concrete is the principal determinant of the concrete39。 s final strength. At one time the instructions for preparing a batch of concrete would have contained proportions such as 1:2:4, indicating that 1 part of Portland cement to 2 parts of sand to 4 parts of gravel by volume were to be mixed together, after which sufficient water was to be added to obtain a workable mixture. This procedure ignored entirely the importance of the watercement ratio. It also resulted very often in the preparation or a very weak concrete, since the natural tendency is to add enough water to make placement of the concrete as easy as possiblethe sloppier the better, as far as the workmen are concerned. This manner of specifying the proportions of concrete is obsolete and should never be followed. In theory, it takes only 3 gal of water to hydrate pletely 1 cu ft of cement. (A sack of cement contains 1 cu ft exactly, and the sack weighs 94 lb). But this watercement ratio produces a mixture that is too stiff to be worked. In practice, therefore, additional water, between 4 and 8 gal per sack of cement, is used to obtain a workable mixture. 5 But the greater the proportion of water in a watercement ratio, the weaker the final concrete will be. The additional water that is necessary to achieve a workable batch will only evaporate from the concrete as the concrete sets, and it will leave behind in the concrete innumerable voids. This is the reason there will always be some porosity in concrete. When an excessive amount of water has been used, there will be an excessive number of voids, which may cause the concrete to leak badly. If these voids should be filled with moisture when cold weather es, they will cause the frost damage alluded to above. As a general rule, therefore, 6 gal of water per sack of cement should be the maximum amount used for making concrete。 and the less the amount of water that is used, the stronger the concrete will be. Also included in the 6 gal is whatever surface moisture is contained in the sand that is part of the aggregate. Mortar is a mixture of a cementitious material (which may be portland cement or lime or both) and sand. When water is added to these ingredients, the result is a plastic substance that is used to bind together bricks, tiles, concrete blocks, and other kinds of masonry units. After the mortar has set, the masonry units are bound together by the ,mortar in such a way that they form a single structural unit. Mortar is closely related to other cementitious materials such as concrete, plaster, and stucco, but it would be a mistake to confuse mortar with these other materials or attempt to use them as a substitute for mortar。 the properties required of each are distinctive and differ from the others. By a mistaken analogy with a chain and its weakest link, it is a mon belief that for any masonry construction to be strong, the mortar must be strong also. Very often, for example, a person who is familiar with concrete will infer that mortar, being a cementitious material like concrete, should have properties similar to those of concrete and be mixed and used in much the same way. w Since, for example, concrete has, or should have, a high pressive strength, mortar should have a high pressive strength also. But the primary function of mortar is to bind the masonry 6 units。