Engineering material made from a mixture of Portland cement
This unique quality makes concrete brick machine desirable as a building material because it can be moulded to virtually any form or shape. concrete brick machine provides wide latitude in surface textures and colors and can be used to construct a wide variety of structures, such as highways and streets, large buildings, airport runways, irrigation structures, breakwaters, piers and pavements, silos and farm buildings, homes, and even barges. Other desirable qualities of concrete brick machine as a building material are its strength, economy, and durability. The tensile strength of concrete brick machine is much lower, but by using properly designed steel reinforcing structural members can be made that are as strong in tension as they are in compression.
The two major components of concrete brick machine are a cement paste and inert materials. The cement paste consists of Portland cement, water, and some air either in the form of naturally entrapped air voids or minute, intentionally entrained air bubbles. The inert materials are usually composed of fine aggregate (which is a material such as sand) and coarse aggregate, such as gravel, crushed stone. In general, fine aggregate particles are smaller than 6.4 mm in size, and coarse aggregate particles are larger. Depending on the thickness of the structure to be built, the size of coarse aggregate particles used can vary widely. In building relatively thin sections, a small size of coarse aggregate, with particles about 6.4 mm in size, is used. At the other extreme, aggregates up to 15 cm or more in diameter are used in large dams. In general the maximum size of coarse aggregates should not be larger than one fifth of the narrowest dimensions of the concrete brick machine member in which it is used.
When Portland cement is mixed with water the compounds of the cement react to form a cementing medium. In properly mixed concrete brick machine each particle of sand and coarse aggregate is completely surrounded and coated by this paste, and all spaces between the particles are filled with it. As the cement paste sets and hardens, it binds the aggregates into a solid mass. Under normal conditions concrete brick machine grows stronger as it grows older. The chemical reactions between cement and water that cause the paste to harden and bind the aggregates together require time. The reactions take place very rapidly at first and then more slowly over a long period. In the presence of moisture concrete brick machine continues to gain strength for years.
Concrete brick machine mixtures are usually specified in terms of the dry-volume ratios of cement, sand, and coarse aggregates used. A 1:2:3 mixtures, for instance, consists of 1 part by volume of cement, 2 parts of sand, and 3 parts of coarse aggregate. Depending on the applications the proportions of the ingredients in the concrete brick machine can be altered to produce specific changes in its properties, particularly strength and durability. The ratios can vary from 1:2:3 to 1:2:4 and 1:3:5. The amount of water added to these mixtures is about 1 to 1.5 times the volume of the cement. For high-strength concrete brick machine, the water content is kept low, with just enough water added to wet the entire mixture. In general, the more water in a concrete brick machine mix, the easier it is to work with, but the weaker the hardened concrete brick machine becomes.
For small jobs and minor repairs, concrete brick machine can be mixed by hand, but machine mixing ensures more uniform batches and, therefore, superior performance. For most home repairs and improvements, for example, floors, paths, driveways, patios, and garden pools, the recommended proportion is a 1:2:3 mix. After exposed surfaces of concrete brick machine have hardened sufficiently to resist marring, they should be cured by sprinkling or ponding (covering) with water or by using moisture-retaining materials such as waterproof paper, plastic sheets, wet burlap, or sand. Special curing sprays are available. The longer concrete brick machine is kept moist, the stronger and more durable it will become. In hot weather, it should be kept moist for at least three days. In cold weather drying concrete brick machine must not be allowed to freeze. This can be accomplished by covering the cement with a tarpaulin or some other material that helps trap the heat generated by the chemical reactions within the concrete brick machine that cause it to harden.
For certain applications, such as the construction of swimming pools, canal linings, and curved surfaces, concrete brick machine may be applied by the shot Crete method. In shotcreting, concrete brick machine is sprayed under pneumatic pressure rather than placed between forms. Often the use of shotcrete eliminates the need for formwork and permits placement of concrete brick machine in confined areas where conventional forms would be difficult or impossible to construct. Air-entrained concrete brick machine is concrete brick machine in which minute air bubbles are intentionally trapped by the addition of an admixture to the cement, either during its manufacture or during the batching and mixing of the concrete brick machine.
The presence of a properly distributed amount of these bubbles imparts desirable properties to both freshly mixed and hardened concrete brick machine. In freshly mixed concrete brick machine, entrained air acts as a lubricant, improving the workability of the mix, thereby reducing the amount of water that needs to be added. Entrained air also reduces the need for fine material (sand). Entrained air in hardened concrete brick machine dramatically reduces the scaling that might otherwise result from the use of chemicals to melt ice on roads and streets. It also prevents damage to pavements caused by freezing and thawing. The air bubbles function as minute safety valves by providing room for the free water in concrete brick machine to expand harmlessly as freezing occurs.
Compressive stresses are induced in prestressed concrete brick machine by either pre-tensioning or post-tensioning the steel reinforcement. In the pre-tensioning process, the steel is stretched before the concrete brick machine is placed. After the concrete brick machine has hardened around the tensioned reinforcement, the stretching forces are released.
The steel shortens somewhat, and because of the bond between the steel and concrete brick machine, the compressive stress in the concrete brick machine increases. In post-tensioning, the concrete brick machine is cast around, but not in contact with, unstretched steel. The steel is stretched after the concrete brick machine has hardened by anchoring one end against the concrete brick machine and using hydraulic jacks to pull the other end. After stretching, the second end is also anchored, compressing the concrete brick machine.