What occurs during the hydration process of concrete?

During the hydration process of concrete, there is a critical chemical reaction that occurs between water and cement. When water is added to cement, it initiates a series of chemical reactions known as hydration. This process forms various compounds, including calcium silicate hydrate and calcium hydroxide, which are essential for developing the strength and durability of the concrete.

This reaction is exothermic, meaning it releases heat, but this released heat contributes to the hardening process rather than directly causing surface cracks. The proper amount of water is vital during this phase because it ensures that the cement particles are adequately saturated to fully react and achieve the desired strength.

In terms of the other options, while water evaporation and temperature changes can influence the curing process and potentially lead to cracking if not managed properly, the fundamental aspect of hydration is the chemical reaction between water and cement, making it the primary explanation for what occurs during this stage.