Explain the process of hydration of cement

Basically, the chemical reaction between cement and water is known as hydration of cement. The reaction takes place between the active components of cement (C4AF, C3A, C3S and C 2S) and water as discussed above.

Now let's look into the process -

When the cement comes in contact with water, the hydration products start depositing on the outer periphery of the nucleus of hydrated cement. This reaction proceeds slowly for 2-5 hours and is called dormant period. As the hydration proceeds, the deposit of hydration products on the original cement grain makes the diffusion of water to unhydrated nucleus more and more difficult, consequently reducing the rate of hydration with time. At any stage of hydration, the cement paste consists of a fine-grained product of hydration having large surface area collectively, the unreacted cement, calcium hydroxide, water and some minor compounds.The crystals of the various resulting compounds gradually fill the space originally occupied by water, resulting in the stiffening of the mass and subsequent development of the strength.

2 C3S + 6H → C3S2H3 + 3 Ca(OH)2

2 C2S + 4H → C3S2H3 + Ca(OH)2