Home / News
Limestone powder in cement2020-12-07 09:17:33
The cement we generally see is also called Portland cement. Chemically speaking, its main components are tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium aluminate, the former two are the main ones.
There are two most important components in cement: one is calcium and the other is silicon. Correspondingly, cement is made by co-firing two types of raw materials: one is limestone, which is calcium carbonate; the other is clay minerals, which is a supplier of silicon. At a high temperature of 1450°C, limestone decomposes into calcium oxide and carbon dioxide. The carbon dioxide is discharged. The calcium oxide continues to react and fuse with clay minerals at high temperatures to form a material with gelling properties. The material that has been cooked is vividly called "clinker".
The clinker is then cooled down extremely quickly by a powerful blower. In this way, the unstable microstructure at high temperatures is maintained. Only by maintaining a lively microstructure, cement can have hydration activity, and can react with water and harden in the future. If the cooling rate is slow, the molecular structure inside the cement will gradually become regular, and the bond between silicon atoms will become very stable. When it is stabilized to the extreme, it will become the most inert thing-sand. After quenching, the clinker is ground into powders with a thickness of several microns to several tens of microns, and a small amount of gypsum is added to control the reaction time.
Limestone is the most readily available and cheapest mixing material for cement plants. It can also improve a series of properties of cement, including reducing the water consumption of cement standard consistency, improving the compatibility of cement and water reducing agents, and improving the water retention of cement. The cement is mixed with about 5% to 8% of limestone instead of clinker, which can increase the early strength of the cement without significantly reducing the late strength of the cement.