外文翻译---波特兰水泥的分法及生产.docx

外文资料译文Portland cement of its Types and Manufacture of Portland cementPortland cement is made by heating a mixture of limestone and clay, or other materials of similar bulk composition and sufficient reactivity, ultimately to a temperature of about 1450C. Partial fusion occurs, and nodules of clinker are produced. The clinker is mixed with a few percent of gypsum and finely ground to make the cement. The gypsum controls the rate of set and may be partly replaced by other forms of calcium sulfate. Some specifications allow the addition of other materials at the grinding stage. The clinker typically has a composition in the region of 67% CaO, 22% SiO2, 5% Al2O3 , 3%Fe2O3 , and 3% of other components,and normally contains four major phases,called alite , belite , aluminate phase and ferrite phase . Several other phases, such as alkali sulfates and calcium oxide, are normally present in minor amounts.Alite is the most important constituent of all normal Portland cement clinkers,of which it constitutes 50%-70%.It is tricalcium silicate (Ca3SiO5)modified in composition and crystal structure by incorporation of foreign ions, especially Mg2+, Al3+ and Fe3+. It reacts relatively quickly with water, and in normal Portland cement is the most important of the constituent phases for strength development at ages up to 28 days, it is by far the most important. Belite constitutes 15%-30% of normal Portland cement clinker. It is declaim silicate (Ca2SiO4) modified by incorporation of foreign ions and normally present wholly or largely as the polymorph. it reacts slowly with water , thus contributing little to the strength during the first 28 days ,but substantially to the further increase in strength that occurs at later ages .By one year, the strength obtainable form pure alit and pure belite are about the same under comparable conditions.The aluminates phase constitutes 5%-10% of most normal Portland cement clinkers. it is Tricalcium aluminates (Ca3Al2O6), substantially modified in composition and sometimes also in structure by incorporation of foreign ions , especially Si4+ , Fe3+, Na+ and K+. It reacts rapidly with water and can cause undesirably rapid setting unless a set-controlling agent, usually gypsum, is added.The ferrite phase makes up 5%-15% of normal Portland cement clinkers. It is tetra calcium aluminoferrite (Ca4AlFeO7) substantially modified in composition by variation in Al/Fe ratio and incorporation of foreign ions. The rate at which it reacts with water appears to be somewhat variable, perhaps due to differences in composition or other characteristics, but in general is high initially and intermediate between those of Alite and Belite at later ages.The great majority of Portland cements made throughout the world are designed for general constructional use. The specifications with which such cements must comply are similar, but not identical, in all countries and various names are used to define the material, such as OPC (Ordinary Portland Cement) in the UK, or Type I Portland Cement in the USA.Specifications are, in general based partly on chemical composition or physical properties such as specific surface area, and partly on performance tests, such as setting time or compressive strength developed under standard conditions. The content of MgO is usually limited to either 4 or 5%, because quantities of this component in excess of about 2% are liable to occur as periclase (magnesium oxide), which through slow reaction with water can cause destructive expansion of hardened concrete. Free lime (calcium oxide) can behave similarly, and its potential formation sets a practical upper limit to the Alite content of a clinker. Excessive contents of SO3 can also lead to delayed expansion, and upper limits of 2.5%-4% are usually imposed. Alkalis (K2O and Na2O) can undergo expansive reactions with certain aggregates, and some national specifications limit the content, e.g. to 0.6% equivalent Na2O (Na2O+0.66K2O) .other upper limit of composition widely used in specifications relate to matter insoluble in dilute acid, and loss on ignition. Many other minor components are limited in content by their effects on the manufacturing process, or the properties, or both, and in some cases the limits are defined in specifications.Rapid-hardening Portland cement have been produced in various ways , such as varying the composition to increase the alite content , finer grinding of the clinker , and improvements in the manufacturing process , e.g. finer grinding or better mixing of the raw materials . The alite contents of Portland cements have increases steadily over the one and a half centuries during which the latter have been produced, and many presentday cements that would be considered normal today would have been described as rapid hardening only a few decades ago. In USA specifications, rapid-hardening Portland cements are called high early strength or Type III cements.Destructive expansion from reaction with sulfates can occur not only if the latter are present in excessive proportion in the cement, but also form attack on concrete by sulfate solutions. The reaction involves the Al2O3 containing phases in the hardened cement, and in sulfate-resisting Portland cements, its effects are reduced by decreasing the proportion of the aluminates phase, sometimes to zero. This is achieved by decreasing the ratio of Al2O3 to Fe2O3 in the materials. In the USA, sulfate-resisting Portland cements are called Type V cements.White Portland cements are made by increasing the ratio of Al2O3 to Fe2O3, and thus represent the opposite extreme in composition to sulfate-resisting Portland cements. The normal, dark color .of Portland cement is due to the ferrite phase, formation of which in white cement must thus be avoided. It is impracticable to employ raw materials that are completely free from Fe2O3 and other components, such as Mn2O3, that contribute to the color. The effects of these components are therefore usually minimized by producing the clinker under slightly reducing conditions and by rapid quenching. In addition to alite, belite and aluminates phase, some glass may be formed.Portland cement is made from some of the earths most abundant materials .about two-thirds of it is derived from calcium oxide, whose source is usually some form of lime-stone(calcium carbonate),marls, chalk, or shells(for example, oyster).the other ingredients-silica,SiO2,about20;alumina ,Al2O3 ,about 5; and iron oxide,Fe2O3,about 3 are derived from sand shale, clays, coal ash, and iron ore metal slag. Because the individual ingredients must be fused and sintered to produce new compounds they must de ground to pass a 200 mesh screen in order to react within a reasonable time in the kiln .in addition, the composition of the raw materials must be held within narrow limits of the above oxides to produce a useful product. Other elemental oxides which can be detrimental to the cement must be limited: these include magnesium MgO; potassium oxide, K2O; sodium oxide, and phosphorus oxide, P2O5.after blending to the proper composition, the raw materials are interground in ball mills, rod mills, or roller millers. Depending on the raw materials characteristics, they are ground either dry (dry process) or in water (wet process). The resultant raw feed is introduced into the kiln system, usually a rotary kiln, where the material is heated to about 2700F. The material progressively loses first the water, then the carbon dioxide CO2, at about 1750F, and at about 2300F, a small amount at liquid phase forms. This liquid is the medium through which the higher-melting phases are formed. The resultant product, called clinker because the whole never truly melts, is cooled and again ground, in ball mills to such a fineness that about 90 will pass a screen having 325 openings per linear inch. The final product has a texture much like face powder. During grinding, about 5 of calcium sulfate(gypsum or anhydride) is added to control setting time, strength development, and other properties.The major trend in manufacture of Portland cement has shifted to a greater emphasis on the reduction of the energy consumed for its production and increasing use of coal to replace gas and oil, which were the major fuels for burning the clinker. Energy consumption is generally greater for the wet process; therefore most new plants use the dry process. The characteristics of the final product are not any different for either process. The worlds largest kiln (as of 1957) produced about 7500 tons (6750 metric tons) per day of clinker. An average kiln produces about 1800 tons (1620 metric tons) per day. The latest kilns utilize some form of preheating system, which fully utilizes the hot exit gases to warm the incoming raw materials; In addition, decarbonation of the limestone can be done on the raw feed prior to its entrance to the rotary kilns by use of auxiliary burners. These techniques enable much shorter rotary kilns for equal production and save much energy. Because of these developments, the worlds longest kiln (760 ft or 228 m long, 25 ft or 7.5 m in diameter) will probably remain the longest. Another trend is toward a newer type of grinding mill, called a roller mill. This mill can use waste heat for drying, lends itself readily to automatic control, and uses less energy. These mills can grind up to 400 tons (360 metric tons) per hour. Several employees in a control room can operate a whole plant except for the quarry. Control is exercised by means of television monitors, sensors, computers, and automatic continuous chemical analysis.Other types of kilns which have been used or are in the process of being developed are vertical or shaft kilns, fluid-bed furnaces, and swirl calciners. 波特兰水泥的分法及生产波特兰水泥是通过加热石灰岩和粘土的混合物，或者其他具有相似组成并具有活性的块状物来生产的，加热的最高温度可以达到大约1450摄氏度。当部分块状物融化时，熟料的结节就出现了。熟料和百分之几的石膏再混合，磨细就制成了水泥。石膏的添加量由率值决定，并且部分其他形式的硫酸钙相化合物可以代替石膏。有些特种水泥允许在研磨阶段加入一些材料。熟料一般由以下成分构成：67的氧化钙，22的二氧化钙，5的三氧化二铝，3的三氧化二铁和3的其他成分。熟料在正常情况下含有三个相：阿利特、贝利特、铝酸三钙及铁铝酸四钙。其他几个相如：碱金属硫酸盐、活性氧化钙等，一般以微小量出现。阿利特是普通波特兰水泥熟料中最重要的组成部分，其构成占5070。它与外来离子（尤其是Mg2+ , Al3+ 和Fe3+）结合在构成上和晶体结构上又发生了变化的硅酸三钙。它与水反应特别快，是普通波特兰水泥28天强度发展的最重要的组成相，这是迄今为止中重要的。贝利特在普通波特兰水泥熟料中占1530。它与外来离子结合并且通常全部或大部分呈晶形的硅酸二钙。它与水反应很慢，因此，在开始的28天内对强度没什么作用。但实际上，它会使以后龄期里的强度进一步增加。一年后，在合适的条件下，纯的阿利特和纯的贝利特获得的强度大约相同。大多数普通波特兰水泥熟料中，铝酸盐相占510。它是在组成和结构上被大幅度的改变，并切有时也和外来离子结合（特别是Si4+ , Fe3+, Na+ and K+）的铝酸三钙。它与水反应迅速，会引起不理想的凝结，除非加入控制凝聚剂，通常加入的是石膏。在普通波特兰水泥熟料中，铁素体相占515。它是在组成上大幅度改变Al/Fe比例和结合外来离子的铁铝酸四钙。也许因为组成和其他特征的差异，氧化铁与水反应的速度似乎有些变动，但总的来说，开始时速度很快，在以后的龄期内处于阿利特预贝利特与水反应的两种速度之间。在整个世界上大多数波特兰水泥的制造是为一般建筑设计的。在世界上所有的国家中，这种水泥的规格遵守类似，但不完全相同。不同的名字被用来定义不同的材料，如英国的普通波特兰水泥，或美国的I型波特兰水泥。一般来说，技术要求部分基于化学组成或物理特性（如比表面积），部分基于性能测试（如凝固时间或标准情况下产生的抗压强度）。氧化镁的含量通常被限制在45之间，因为大量的这部分氧化镁超过2时容易形成方镁石，通过雨水的缓慢反应可能会使已硬化的混凝土发生膨胀性的破坏。游离氧化钙便显出相同的作用，并且它在一定程度上限制了水泥熟料中阿利特含量的上限。三氧化硫的含量过高也能导致延迟膨胀，通常设置2.54含量的上限。碱金属（氧化钾和氧化钠）可通过膨胀反应形成一定量的骨料，并且一些国家的规格限制它的含量，例如：0.6相当量的钠。其他上限组成被广泛用于规范涉及物质不溶于稀酸技术和灼烧损失。许多其他次要成分在对其生产过程中，其含量也被限制，或者性质，或者两者都有，并且在某些情况下，其规格是被限制的。快硬波特兰水泥已经用给各种方式生产出来，例如使阿利特含量增加来改变熟料组成，细末熟料并且对生产过程进行改进，如细磨或者加入更好的混合材料。波特兰水泥中阿利特的含量在过去的一个半世纪期间一直在平稳地增加，加入更好的混合材料也仅仅就在几十年前就已经出现了，和许多现代水泥一样，将被视为正常的快速硬化。在美国水泥规格中，快硬波特兰水泥被称为早期强度高或III型水泥。来自于硫酸盐反应的破坏性扩张反应不仅会出现过度比例的水泥，也会形成对混凝土侵蚀的硫酸盐溶液。在水泥硬化阶段所设计的氧化铝相反应在耐硫酸盐波特兰水泥中，其影响可以降低通过减少铝酸盐的比例，有时其影响可降低至为零。这是通过减少三氧化二铝与三氧化二铁的比例来得到的。在美国，耐硫酸盐波特兰水泥被称为V型水泥。波特兰白水泥是由增加三氧化二铝对三氧化二铁的比例来制成的，从而代表了由另一个极端组成的耐硫酸盐波特兰水泥。在通常情况下，颜色较深的波特兰水泥是由于含有铁素体相的形成，因此在白色水泥中必须避免铁素体相的形成。使用完全不含三氧化二铁及其其他有助颜色成分的材料（例如二氧化锰），是不切实际的。在生产熟料过程中，这些成分的影响可以通过减少其还原性