- Time:Jan 31, 2023
The following factors affect the setting and hardening of cement.
1. Clinker mineral composition: mineral composition is a direct factor affecting the setting and hardening of cement. Change the mineral composition of cement, its setting and hardening situation will be significantly changed.
2. Cement fineness: fineness refers to the degree of coarseness of the powder material. The finer the cement particles - the larger the contact area with water, the faster the hydration reaction, the faster the setting and hardening, the greater the early strength.
3. The amount of mixing water: in order to make the cement paste with plasticity and fluidity, the amount of water added usually exceeds the amount of water required when the cement is fully hydrated. Excess water in the cement stone to form capillary pores, the greater the water-cement ratio, the greater the capillary porosity of the hardened cement stone, the strength of the cement stone cooling temperature and humidity is low. Water-cement ratio directly affects the porosity of hardened cement stone, and is closely related to the strength of cement stone.
4. Environmental temperature and humidity: under proper temperature and humidity conditions, the hydration, setting and hardening of cement will be faster. The temperature rises, the hydration reaction of cement accelerates, so that the rate of setting and hardening is accelerated, and the early strength increases, but on the contrary, the late strength may be reduced. The ageing is accelerated and the early strength increases, but to the later strength may instead decrease. On the contrary, at reduced temperature, the setting and hardening rate of cement is slow and the early strength is low. At negative temperatures, cement hydration will stop. Water is necessary for the hydration and hardening of cement, such as water retention and maintenance.
5. Conditioning time (age): the hydration and setting hardening of cement is a gradual process with the extension of time. In the early stage, the hydration rate is fast and the strength development is relatively fast, and then gradually decreases and tends to be stable.
6. The amount of gypsum: gypsum can be explained as follows: when the cement hydrates, gypsum quickly acts with tricalcium aluminate to generate hydrated calcium sulfur aluminate (calcium alumina), calcium alumina is difficult to dissolve in water, it precipitates on the surface of cement particles to form a protective film, which hinders the hydration reaction of tricalcium aluminate, thus controlling the hydration reaction rate of cement and delaying the setting time. However, too much of it will cause expansion and cracking.
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