土木畢業(yè)設(shè)計(jì)外文翻譯.doc

山東建筑大學(xué)畢業(yè)設(shè)計(jì)外文文獻(xiàn)及譯文本科畢業(yè)論文外文文獻(xiàn)及譯文文獻(xiàn)、資料題目：Concrete院 （部）： 土木工程學(xué)院專 業(yè)： 土木工程班 級： 土木105姓 名： 王洪良學(xué) 號： 2010011424指導(dǎo)教師： 張鑫 劉清陽翻譯日期：2014/6/14ConcreteWikipediaThis article is about the construction material. For other uses, see Concrete (disambiguation).Concrete is a construction material that consists of cement (commonly Portland cement), aggregate (generally gravel and sand), water and admixtures.Concrete solidifies and hardens after mixing and placement due to a chemical process known as hydration. The water reacts with the cement, which bonds the other components together, eventually creating a stone-like material. It is used to make pavements, architectural structures, foundations, motorways/roads, overpasses, parking structures, brick/block walls and footings for gates, fences and poles.Concrete is used more than any other manmade material on the planet.1 As of 2005 about six billion cubic meters of concrete are made each year, which equals one cubic meter for every person on Earth. Concrete powers a US $35 billion industry which employs over two million workers in the United States alone. Over 55,000 miles of freeways and highways in America are made of this material. The Peoples Republic of China currently consumes 40% of world cement concrete production.Contents 1 History 2 Composition o 2.1 Cement o 2.2 Water o 2.3 Aggregates o 2.4 Chemical admixtures o 2.5 Mineral admixtures and blended cements o 2.6 Fibers 3 Mixing concrete 4 Characteristics o 4.1 Workability o 4.2 Curing o 4.3 Strength o 4.4 Elasticity o 4.5 Expansion and shrinkage o 4.6 Cracking 4.6.1 Shrinkage cracking 4.6.2 Tension cracking o 4.7 Creep 5 Damage modes o 5.1 Fire o 5.2 Aggregate expansion o 5.3 Sea water effects o 5.4 Bacterial corrosion o 5.5 Chemical attacks 5.5.1 Carbonation 5.5.2 Chlorides 5.5.3 Sulphates o 5.6 Leaching o 5.7 Physical damage 6 Types of concrete o 6.1 Regular concrete o 6.2 High-strength concrete o 6.3 High-performance concrete o 6.4 Self-compacting concretes o 6.5 Shotcrete o 6.6 Pervious concrete o 6.7 Cellular concrete o 6.8 Cork Cement Composites o 6.9 Roller-compacted concrete o 6.10 Glass concrete o 6.11 Asphalt concrete 7 Concrete testing 8 Concrete recycling 9 Use of concrete in structures o 9.1 Mass concrete structures o 9.2 Reinforced concrete structures o 9.3 Prestressed concrete structures 10 See also 11 References 12 External links HistoryIn Serbia, remains of a hut dating from 5600 BCE have been found, with a floor made of red lime, sand, and gravel. The pyramids of Shaanxi in China, built thousands of years ago, contain a mixture of lime and volcanic ash or clay.2The Assyrians and Babylonians used clay as cement in their concrete. The Egyptians used lime and gypsum cement. In the Roman Empire, concrete made from quicklime, pozzolanic ash / pozzolana and an aggregate made from pumice was very similar to modern Portland cement concrete. The discovery of concrete was lost for 13 centuries until in 1756, the British engineer John Smeaton pioneered the use of Portland cement in concrete, using pebbles and powdered brick as aggregate. In modern times the use of recycled materials as concrete ingredients is gaining popularity because of increasingly stringent environmental legislation. The most conspicuous of these is fly ash, a byproduct of coal fired power plants. This has a significant impact by reducing the amount of quarrying and landfill space required. The properties of concrete have been altered since Roman and Egyptian times, when it was discovered that adding volcanic ash to the mix allowed it to set under water. Similarly, the Romans knew that adding horse hair made concrete less liable to shrink while it hardened, and adding blood made it more frost resistant. In modern times, researchers have added other materials to create concrete that is extremely strong, and even concrete that can conduct electricity.CompositionThe composition of concrete is determined initially during mixing and finally during placing of fresh concrete. The type of structure being built as well as the method of construction determine how the concrete is placed and therefore the composition of the concrete mix (the mix design).CementPortland cement is the most common type of cement in general usage. It is a basic ingredient of concrete, mortar and plaster. English engineer Joseph Aspdin patented Portland cement in 1824; it was named because of its similarity in colour to Portland limestone, quarried from the English Isle of Portland and used extensively in London architecture. It consists of a mixture of oxides of calcium, silicon and aluminium. Portland cement and similar materials are made by heating limestone (a source of calcium) with clay, and grinding this product (called clinker) with a source of sulfate (most commonly gypsum). When mixed with water, the resulting powder will become a hydrated solid over time.High temperature applications, such as masonry ovens and the like, generally require the use of a refractory cement; concretes based on Portland cement can be damaged or destroyed by elevated temperatures, but refractory concretes are better able to withstand such conditions.WaterPotable water can be used for manufacturing concrete. The water/cement ratio (mass ratio of water to cement) is the key factor that determines the strength of concrete. A lower w/c ratio will yield a concrete which is stronger and more durable, while a higher w/c ratio yields a concrete with a larger slump, so it may be placed more easily.3 Cement paste is the material formed by combination of water and cementitious materials; that part of the concrete which is not aggregate or reinforcing. The workability or consistency is affected by the water content, the amount of cement paste in the overall mix and the physical characteristics (maximum size, shape, and grading) of the aggregates.AggregatesThe water and cement paste hardens and develops strength over time. In order to ensure an economical and practical solution, both fine and coarse aggregates are utilised to make up the bulk of the concrete mixture. Sand, natural gravel and crushed stone are mainly used for this purpose. However, it is increasingly common for recycled aggregates (from construction, demolition and excavation waste) to be used as partial replacements of natural aggregates, whilst a number of manufactured aggregates, including air-cooled blast furnace slag and bottom ash are also permitted.Decorative stones such as quartzite, small river stones or crushed glass are sometimes added to the surface of concrete for a decorative exposed aggregate finish, popular among landscape designers.Chemical admixturesPlasticizers (water-reducing admixtures) increase the workability of plastic or fresh concrete, allowing it be placed more easily, with less consolidating effort. Superplasticizers (high-range water-reducing admixtures) are a class of plasticizers which have fewer deleterious effects when used to significantly increase workability. Alternatively, plasticizers can be used to reduce the water content of a concrete (and have been called water reducers due to this application) while maintaining workability. This improves its strength and durability characteristics. Pigments can be used to change the color of concrete, for aesthetics. Corrosion inhibitors are used to minimize the corrosion of steel and steel bars in concrete. Bonding agents are used to create a bond between old and new concrete. Pumping aids improve pumpability, thicken the paste, and reduce dewatering of the paste. Mineral admixtures and blended cementsThere are inorganic materials that also have pozzolanic or latent hydraulic properties. These very fine-grained materials are added to the concrete mix to improve the properties of concrete (mineral admixtures),4 or as a replacement for Portland cement (blended cements).5 Fly ash: A by product of coal fired electric generating plants, it is used to partially replace Portland cement (by up to 60% by mass). The properties of fly ash depend on the type of coal burnt. In general, silicious fly ash is pozzolanic, while calcareous fly ash has latent hydraulic properties.6 Ground granulated blast furnace slag (GGBFS or GGBS): A by product of steel production, is used to partially replace Portland cement (by up to 80% by mass). It has latent hydraulic properties.7 Silica fume: A byproduct of the production of silicon and ferrosilicon alloys. Silica fume is similar to fly ash, but has a particle size 100 times smaller. This results in a higher surface to volume ratio and a much faster pozzolanic reaction. Silica fume is used to increase strength and durability of concrete, but generally requires the use of superplasticizers for workability.8 High Reactivity Metakaolin (HRM): Metakaolin produces concrete with strength and durability similar to concrete made with silica fume. While silica fume is usually dark gray or black in color, high reactivity metakaolin is usually bright white in color, making it the preferred choice for architectural concrete where appearance is important. FibersShort fibers of steel, glass, synthetic or natural materials can be incorporated in the concrete during mixing. See Fiber reinforced concrete.Mixing concreteThorough mixing is essential for the production of uniform, high quality concrete. Therefore, equipment and methods should be capable of effectively mixing concrete materials containing the largest specified aggregate to produce uniform mixtures of the lowest slump practical for the work. Separate paste mixing has shown that the mixing of cement and water into a paste before combining these materials with aggregates can increase the compressive strength of the resulting concrete.9 The paste is generally mixed in a high-speed, shear-type mixer at a w/cm of 0.30 to 0.45 by mass. The premixed paste is then blended with aggregates and any remaining batch water, and final mixing is completed in conventional concrete mixing equipment.10High-Energy Mixed Concrete (HEM concrete) is produced by means of high-speed mixing of cement, water and sand with net specific energy consumption at least 5 kilojoules per kilogram of the mix. It is then added an plasticizer admixture and mixed after that with aggregates in conventional mixer. This paste can be used itself or foamed (expanded) for lightweight concrete.11 Sand effectively dissipates energy in this mixing process. HEM concrete fast hardens in ordinary and low temperature conditions, and possesses increased volume of gel, drastically reducing capillarity in solid and porous materials. It is recommended for precast concrete in order to reduce quantity of cement, as well as concrete roof and siding tiles, paving stones and lightweight concrete block production.CharacteristicsDuring hydration and hardening, concrete needs to develop certain physical and chemical properties. Among other qualities, mechanical strength, low moisture permeability, and chemical and volumetric stability are necessary.WorkabilityWorkability (or consistence, as it is known in Europe) is the ability of a fresh (plastic) concrete mix to fill the form / mould properly with the desired work (vibration) and without reducing the concretes quality. Workability depends on water content, aggregate (shape and size distribution), cementitious content and age (level of hydration), and can be modified by adding chemical admixtures. Raising the water content or adding chemical admixtures will increase concrete workability. Excessive water will lead to increased bleeding (surface water) and/or segregation of aggregates (when the cement and aggregates start to separate), with the resulting concrete having reduced quality. The use of an aggregate with an undesirable gradation can result in a very harsh mix design with a very low slump, which cannot be readily made more workable by addition of reasonable amounts of water.Workability can be measured by the slump test, a simplistic measure of the plasticity of a fresh batch of concrete following the ASTM C 143 or EN 12350-2 test standards. Slump is normally measured by filling an Abrams cone with a sample from a fresh batch of concrete. The cone is placed with the wide end down onto a level, non-absorptive surface. When the cone is carefully lifted off, the enclosed material will slump a certain amount due to gravity. A relatively dry sample will slump very little, having a slump value of one or two inches (25 or 50 mm). A relatively wet concrete sample may slump as much as six or seven inches (150 to 175 mm).Slump can be increased by adding chemical admixtures such as mid-range or high-range water reducing agents (super-plasticizers) without changing the water/cement ratio. It is bad practice to add extra water at the concrete mixer.High-flow concrete, like self-consolidating concrete, is tested by other flow-measuring methods. One of these methods includes placing the cone on the narrow end and observing how the mix flows through the cone while it is gradually lifted.CuringBecause the cement requires time to fully hydrate before it acquires strength and hardness, concrete must be cured once it has been placed. Curing is the process of keeping concrete under a specific environmental condition until hydration is relatively complete. Good curing is typically considered to provide a moist environment and control temperature. A moist environment promotes hydration, since increased hydration lowers permeability and increases strength resulting in a higher quality material. Allowing the concrete surface to dry out excessively can result in tensile stresses, which the still-hydrating interior cannot withstand, causing the concrete to crack.Also, the amount of heat generated by the exothermic chemical process of hydration can be problematic for very large placements. Allowing the concrete to freeze in cold climates before the curing is complete will interrupt the hydration process, reducing the concrete strength and leading to scaling and other damage or failure.The effects of curing are primarily a function of geometry (the relation between exposed surface area and volume), the permeability of the concrete, curing time, and curing history.Improper curing can lead to several serviceability problems including cracking, increased scaling, and reduced abrasion resistance.StrengthConcrete has relatively high compressive strength, but significantly lower tensile strength (about 10% of the compressive strength). As a result, concrete always fails from tensile stresses even when loaded in compression. The practical implication of this is that concrete elements subjected to tensile stresses must be reinforced. Concrete is most often constructed with the addition of steel or fiber reinforcement. The reinforcement can be by bars (rebar), mesh, or fibres, producing reinforced concrete. Concrete can also be prestressed (reducing tensile stress) using internal steel cables (tendons), allowing for beams or slabs with a longer span than is practical with reinforced concrete alone.The ultimate strength of concrete is influenced by the water-cement ratio (w/c) water-cementitious materials ratio (w/cm), the design constituents, and the mixing, placement and curing methods employed. All things being equal, concrete with a lower water-cement (cementitious) ratio makes a stronger concrete than a higher ratio. The total quantity of cementitious materials (Portland cement, slag cement, pozzolans) can affect strength, water demand, shrinkage, abrasion resistance and density. As concrete is a liquid which hydrates to a solid, plastic shrinkage cracks can occur soon after placement; but if the evaporation rate is high, they often can occur during finishing operations (for example in hot weather or a breezy day). Aggregate interlock and steel reinforcement in structural members often negates the effects of plastic shrinkage cracks, rendering them aesthetic in nature. Properly tooled control joints or saw cuts in slabs provide a plane of weakness so that cracks occur unseen inside the joint, making a nice aesthetic presentation. In very high strength concrete mixtures (greater than 10,000 psi), the strength of the aggregate can be a limiting factor to the ultimate compressive strength. In lean concretes (with a high water-cement ratio) the use of coarse aggregate with a round shape may reduce aggregate interlock.Experimentation with various mix designs begins by specifying desired workability as defined by a given slump, durability requirements, and the required 28 day compressive strength. The characteristics of the cementitious content, coarse and fine aggregates, and chemical admixtures determine the water demand of the mix in order to achieve the desired workability. The 28 day compressive strength is obtained by determination of the correct amount of cementitious to achieve the required water-cement ratio. Only with very high strength concrete does the strength and shape of the coarse aggregate become critical in determining ultimate compressive strength.The internal forces in certain shapes of structure, such as arches and vaults, are predominantly compressive forces, and therefore concrete is the preferred construction material for such structures.W reported on April 13th, 2007, that a team from the University of Tehran, competing in a contest sponsored by the American Concrete Institute, demonstrated several blocks of concretes with abnormally high compressive strengths between 50,000 and 60,000 PSI at 28 days1. The blocks appeared to use an aggregate of steel fibres and quartz - a mineral with a compressive strength o