文档介绍：Portland Cement
Portland cement is made by heating a mixture of limestone and clay ,or the other materials of similar blinkers .It is tricalcium aluminate (Ca3Al2O6) ,substantially modified in composition and sometimes also in structure by ionic substitutions .It reacts rapidly with water ,and cause undesirably rapid setting unless a set controlling agent , usually gypsum ,is used .
Ferrite makes up 5%15% of normal Portland cement clinkers .It is tetracalcium aluminoferrite (Ca2AlFeO5) , substantially modified in composition by variation in Al/Fe ratio and ionic substitutions .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 low or very low at later ages.
Types of Portland cement
The great majority of Portland cements made throughout the world are designed for general constructional use .The standard 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 Class Portland cement in current European and British standards( is the minimum 28-days compressive strength in MPa) , TypeⅠ and Ⅱ Portland cement in the ASTM (American Society for Testing and Materials) specifications used in the USA ,or Ordinary Portland Cement(OPC) in former Bri