外文翻譯---波特蘭水泥的分法及生產(chǎn)(文件)
【正文】 ases, 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 position 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 theβ 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 parable conditions.The aluminates phase constitutes 5%10% of most normal Portland cement clinkers. it is Tricalcium aluminates (Ca3Al2O6), substantially modified in position 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 setcontrolling 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 position 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 position 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 ply 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 position or physical properties such as specific surface area, and partly on performance tests, such as setting time or pressive strength developed under standard conditions. The content of MgO is usually limited to either 4 or 5%, because quantities of this ponent in excess of a
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