水泥是如何制造的

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Portland cement is the basic ingredient of concrete. 混凝土 is formed when portland cement creates a paste with water that binds with sand and rock to harden.

Cement is manufactured through a closely controlled chemical combination of calcium, silicon, 铝, 铁和其他成分.

Common materials used to manufacture cement include limestone, shells, 以及白垩或泥灰岩与页岩的结合, clay, slate, 高炉矿渣, 硅砂, 和铁矿石. 这些成分, when heated at high temperatures form a rock-like substance that is ground into the fine powder that we commonly think of as cement.

利兹的砖匠约瑟夫·阿斯丁, England first made portland cement early in the 19th century by burning powdered limestone and clay in his kitchen stove. 用这种粗糙的方法, he laid the foundation for an industry that annually processes literally mountains of limestone, clay, 水泥石, and other materials into a powder so fine it will pass through a sieve capable of holding water. 

Cement plant laboratories check each step in the manufacture of portland cement by frequent chemical and physical tests. The labs also analyze and test the finished product to ensure that it complies with all industry specifications.

The most common way to manufacture portland cement is through a dry method. The first step is to quarry the principal raw materials, mainly limestone, clay, and other materials. 岩石采石后被压碎. 这涉及到几个阶段. The first crushing reduces the rock to a maximum size of about 6 inches. The rock then goes to secondary crushers or hammer mills for reduction to about 3 inches or smaller.

The crushed rock is combined with other ingredients such as iron ore or fly ash and ground, mixed, 然后送入水泥窑.

The cement kiln heats all the ingredients to about 2,700 degrees Fahrenheit in huge cylindrical steel rotary kilns lined with special firebrick. Kilns are frequently as much as 12 feet in diameter—large enough to accommodate an automobile and longer in many instances than the height of a 40-story building. The large kilns are mounted with the axis inclined slightly from the horizontal.

The finely ground raw material or the slurry is fed into the higher end. At the lower end is a roaring blast of flame, produced by precisely controlled burning of powdered coal, oil, 可替代燃料, 或在强制通风下的气体.

As the material moves through the kiln, certain elements are driven off in the form of gases. The remaining elements unite to form a new substance called clinker. Clinker comes out of the kiln as grey balls, about the size of marbles.

Clinker is discharged red-hot from the lower end of the kiln and generally is brought down to handling temperature in various types of coolers. The heated air from the coolers is returned to the kilns, a process that saves fuel and increases burning efficiency.

熟料冷却后, cement plants grind it and mix it with small amounts of gypsum and limestone. Cement is so fine that 1 pound of cement contains 150 billion grains.  The cement is now ready for transport to ready-mix concrete companies to be used in a variety of construction projects.

Although the dry process is the most modern and popular way to manufacture cement, some kilns in the United States use a wet process. The two processes are essentially alike except in the wet process, the raw materials are ground with water before being fed into the kiln.