Building materials appeared at the moment when at the dawn of our civilization the first people began the construction of houses and fortifications. After lengthy searches and experiments, it was revealed that finely crushed limestone and gypsum, when mixed with water and minerals, acquire special astringent properties.
After hardening, it forms a monolithic compound having the characteristics of a solid stone. From that moment, cement began to be produced in large quantities and used in the construction of large and small structures. Passing once again past a building made of stone and metal, we often ask ourselves: “So how is cement made?”
Interesting fact: during the construction of the Egyptian pyramids, the pharaohs used a technology similar to the production of concrete. A mixture of crushed limestone and stone chips was poured with water and turned into monolithic stone blocks.
What is cement made of?
The first stage of production begins in the limestone quarry when components of the future cement are removed from the soil with the help of mining machines. In order for the building material to have the required strength, limestone is chosen for production, which lies close to the surface. In its composition, in large quantities, there is silicon, iron and aluminum oxide. If you dig deeper, the breed will be cleaner, but with a high content of calcium carbonate. The extracted stone, if necessary, is sorted and sent to production, where the proportions are changed to obtain cement of different grades.
Limestone processing
At a cement plant, the rock is discharged into an apparatus for primary crushing of stones. Large boulders under the influence of a pressing force of several tons are gradually crushed to the size of a tennis ball and fed to the conveyor. Small and large stones are sent to secondary crushing, where they are reduced to the size of a golf ball and into fine powder. Limestone, with a different percentage of calcium carbonate, is treated separately.
This is necessary for their further mixing in different proportions and according to a certain technology in order to produce cement of different grades.
Sorting and grinding
Fine limestone, using a sorting loader, is placed in dry warehouses, protected from moisture and temperature extremes. Heaps are formed from a raw mix of different composition, ready for the grinding step. Through the conveyor, crushed stone enters the grinder - a roller mill, in which limestone dust is generated.
Mixing
To create cement of different grades, iron, aluminum dioxide and silicon are added to the prepared rock. The composition and amount of additives is determined after a chemical study of limestone. The roller evenly mixes the components of cement, until a homogeneous powder without stones. Upon completion of the process, the finished mixture is sent to heat treatment.
Heat treatment
The powder is sent to a furnace in which, under the influence of a temperature of 800 ° C, the process of chemical bonding of mineral components begins in stone flour.After the first heat treatment, it is sent to a calciner, where, using a chemical reaction, 95 - 97% carbon dioxide is removed in a few seconds and lime is separated. Then the mixture is sent to a rotary cylindrical furnace, in which it is slowly mixed under the influence of a temperature of 1500 - 1800 ° C.
With prolonged exposure to high temperature, the powder turns into a glassy formation called “clinkers”. Upon exit from the furnace, clinkers are cooled to 60 - 80 ° C, sent to the drive and then for crushing.
Final crushing
The clinker is placed in a rotating drum, with metal balls inside. Gypsum is added to the contents, the amount of which depends on the brand of cement. Under the influence of rotational movements and movement of balls, the mixture is crushed to a powder form - this is the finished cement.
Interesting fact: a surge in concrete production began in the 19th century after Joseph Espdin patented cement called Portland cement, which has the strength of natural stone, in 1824.
Cement production takes place in specialized plants using friction and thermal energy. At the same time, limestone rocks slowly turn into cement. Upon completion of the process, the finished product can be used for the construction of any structures, large and small sizes.
