Calcium silicate
Calcium silicate (碳酸三钙) is an inorganic compound, molecular formula Ca3SiO5, molecular weight of 228.3165, is one of the components of cement. Calcium silicate hydrate reaction is fast, hydration heat release is large.
The main components of ordinary cement are the three-calcium silicate (3CaO SiO2), the second-calcium silicate (2CaO SiO2) and the three-calcium aluminate (3CaO Al2O3). The sintering of limestone and clay is Portland cement, whose main ingredient is Calcium silicate. In the process of mixing cement, if the quartz sand (yellow sand) is added to form a harmonic material commonly known as "Sanhe earth", or placed inside the cement steel bar (commonly known as reinforced cement), then its mechanical strength is greater.
Its chemical properties are as follows: white solid. Pure Calcium silicatereaction diffusion was only stable in the temperature range of 1250 to 2065℃, inconsistent fused into calcium oxide and liquid phase above 2065℃, and decomposed into dialcium silicate and calci
um oxide below 1250℃. Under acute and cold conditions, the decomposition speed of three-calcium silicate is slow, so that it can exist in a metastable state at room temperature. Calcium silicate can be generated by calcium oxide and silica at high temperature, or by dicalcium silicate and calcium oxide. Calcium silicate is the main mineral of cement clinker containing up to 50% or more.
The hydration process of Calcium silicate is divided into five stages: induction early stage (15min), induction period, acceleration period, decline period and stability period.
a.Early induction: a sharp chemical reaction occurs immediately after adding water, but for a short duration and ends within 15min.
b.Induction period: The reaction rate is extremely slow, lasting for 2~4h (the cement slurry remains plastic). The initial coagulation time is basically equivalent to the end of the induction period.
c.Acceleration period: the reaction is accelerated again, the reaction rate increases with time, and the second exothermic peak appears. This stage ends at the peak time (4~8h), when the final coagulation time has passed, and the cement stone begins to harden.
d.Reducation period: hydration attenuation period, the reaction rate decreases with time (12~24h), hydration is gradually controlled by the diffusion rate.
e.Stability period: the reaction rate is very low, the reaction process is basically stable, and the hydration is completely controlled by the diffusion rate.

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