How is cement made so much more complicated than I thought

Nowadays, people like to raise flowers and plants at home or in the office, and it is very important to choose a beautiful and suitable flower pot. Now there are many short videos on the Internet to introduce DIY cement vases. People have rich imagination to make a variety of cement flower POTS, and use cement to make stools, plates and other supplies.

The cement floor of the home will try to be decorated again, either wood floors or tiles, but with the changes of The Times, people's aesthetic has also changed, began to like simple and simple decoration style, with a sense of metal cement floor and wall is liked by everyone, once abandoned cement has come back to find its own value, but also become a popular element.

Cement is also called "putty" when we were young, for the powder, the main composition is limestone and clay and iron ore powder, mixed with water into a slurry, after hardening can become a solid building material, modern construction Bridges, houses, roads and so on have cement credit.

The development history of cement

At the beginning, human beings had no buildings, living in caves or trees, and later began to build houses with branches or thatch.

As man began to use various tools to build strong houses out of stone, earth, and wood, various construction materials came into use.

Cement was first used in ancient Rome, using volcanic ash and lime with water to bind stones together and make structures stronger.

In the Southern and Northern Dynasties of China, the mixture of lime, clay and glutinous rice was first used to bond building materials and build tombs.

In 1796, the British used marl to make cement, which became the first modern cement.

In 1824, the United Kingdom invented Portland cement and obtained the patent for cement.

Li Hongzhang founded China's first cement factory in Tangshan in 1889.

China's cement industry after hundreds of years of development, as early as 2003, the annual output of cement 860 million tons, accounting for about 40% of the world's total output.

Principle of cement setting and hardening

After adding the right amount of water to the cement, it will become a slurry that can be processed at will, and it will solidify into a tight solid over time. If you start by adding stones or sand, it will become what we call concrete. This process is the solidification and hardening of cement.

The solidification and hardening of cement is a complex process. Substances in cement react with water, and some small crystals are initially formed and wrapped on the surface of cement particles. These small crystals are bonded together by a very small attraction, thus forming a network structure called solidified structure. Therefore, the strength of this structure is very low, and it has obvious plasticity.

As time goes on, the material in the cement reacts with the water, the cement particles begin to dissolve and shrink, and the coating on the surface, like a million seeds, begins to grow outward into thin fibers, and the fibers grow inward into the cement particles, and finally form an object like a hedgehog, which is so small that we can only see the hard surface of the cement with the naked eye.

As the water in the cement drains away over time, the fibers become more and more connected to each other, and eventually form a solid whole. The process of cement strength is the process of burring cement particles together. When faced with unbearable gravity, these burrs will break, and the cement will crack.

There are many factors that affect the setting rate and hardening strength of cement, such as temperature, water amount, and different kinds of admixtures.

The production process of cement

The main raw materials of cement are natural limestone as well as sand and iron, and after complex processing, the final product is a super glue that is used to add water.

The extracted limestone is first crushed, and the crushed limestone is sent through a conveyor belt to the machine, where it is crushed again to the size of a golf ball.

Crushed limestone is sent into the hopper, after adding iron and sand and clay, the proportion of the addition is controlled by the machine, and the mixed ore is crushed again, in this process, the dust suction will absorb the stone powder, the material is sent into the screen, and then the impurities will be screened away, now these are raw materials, but also use high temperature, heating to 1600℃ and then mixing other components, The high temperatures can set off a chain of chemical reactions that turn the mixed materials into cement, which must be stripped of carbon dioxide in order for them to harden when exposed to water.

The stone powder is sent into the high-temperature kiln, and the kiln keeps rotating to drive the stone powder inside to keep turning, just like the dehydration of the washing machine, when the mixture from one end of the kiln to the other end, the temperature will reach 1500 ° C, and after burning at this temperature, it will become a material with gelling properties.

This material is "cooked" by high temperature is also called "material", which is cooled, mixed with the last component gypsum, it can slow down the chemical reaction when adding water to the cement, and the material and gypsum are directly sent to the ball mill, the raw material is ground into fine powder, you can bag and sell.

Strength of cement

The strength of cement is an important criterion for evaluating the quality of cement and an important basis for dividing the strength grade. The strength of cement refers to the maximum destructive force it can withstand per unit area after hardening, which is expressed by MPa (mpa).

We will see that the cement bag is marked with the words 52.5, which refers to the strength level of the cement, meaning that the standard specimen can withstand a maximum pressure of 52.5 mpa, and the words such as 52.5R, R means early strength, indicating that this cement can reach a higher strength in the early (short time).

Since the cement, the building is higher and higher, the road is longer and longer, the size of the city is also getting larger and larger, these have the credit of cement, it is one of the essential basic materials for the construction of modern society, cement has changed the face of the earth, known as one of the inventions to promote human civilization, is the cornerstone of human civilization.

However, some people have listed cement as one of the worst inventions in the history of mankind. Why?