For ages, humans have been using a binding material to make brick walls and firm structures to dwell in. Limestone was the earliest binder, and the quest to obtain desirable characteristics derived the cement, the ultimate binding material.
It is a substance which not only sets fast, but also hardens as time passes. It also has the most noteworthy quality of binding almost any material. The word cement has a Roman descent. They described the structures made from crushed rock bound with burnt lime, by the term opus caementicium.
But, the procedure of making the modern-day cement involves using some state-of-the-art techniques. Here are the various chemical and thermal processes which are involved in manufacturing cement:
Limestone and clay is mined from quarries by drilling or setting off explosions in the rock. Large limestone rocks and boulders are fragmented into smaller pieces, and transported to the cement-making plant using either huge dump trucks or high-capacity conveyor belts.
These medium-sized rocks now go through the first process in the plant. Here, they are put into heavy crushers which break down the rocks in marble-sized pieces (approx 1½ inch in size).
This is a very important process of proportionally mixing the different raw materials. The limestone pieces are added to a blender, where they are mixed with other raw materials in the exact required proportion.
Raw Material Milling
A vertical steel mill is made use of in this process, which further grinds the blended material using the pressure exerted by three conical rollers. The rolling of these three rollers on the turning milling table crushes the blend in fine powder. Sometimes, horizontal crushing mills are also used in this process.
This is the most important core process, wherein the crushed and blended raw material goes into a huge and extremely hot rotating kiln to undergo a process called sintering. In this phase, the raw blend turns into a sort of partially-molten state.
The raw materials reach about 2700°F (1480°C) inside the furnace. This state facilitates some chemical and physical processes in the raw material. The resultants coming out of the furnace are small, dark gray, red-hot nodules called clinker, which are 1-2 inches in diameter.
These clinkers are cooled and grounded into a fine gray powder. To extend the cement's setting time, small amount of gypsum is added during this process as this powder makes its way through the mill's two chambers. This is now the finished product and is called Portland cement or simply cement.
Cement is one of the most important commodities today, and its production and consumption is constantly on the rise. China is the largest manufacturer of this material in the world, and accounts for about 45% of the world's cement. India and the USA are distant 2nd and 3nd respectively, with 6.5% and 4.5% of world's cement production respectively.
Cement manufacturing also has its environmental effects. The industry is responsible for emitting about 5% of the global CO2 emissions. Nearly 900 kg of CO2 is emitted for every 1000 kg of cement produced. The burning of fossil fuels produces other polluting gases as well.