What happens during the hydration process of concrete?

During the hydration process of concrete, an exothermic reaction occurs as the compounds in the cement, primarily tricalcium silicate and dicalcium silicate, react with water. This reaction releases heat, which is why it is classified as exothermic. The heat generated is crucial for the curing process, aiding in the development of concrete's strength and durability. The heat not only drives the chemical reactions forward but also helps prevent issues such as freezing in cold weather, allowing for proper setting and hardening of the concrete.

The other options do not accurately describe the hydration process. Concrete does not primarily absorb moisture from the air during this process, nor does it inherently become cold; in fact, it becomes warmer due to the heat released. Lastly, while air does play a role in the curing process—particularly in terms of moisture retention—it does not mix with the concrete in a way that affects hydration directly. All these aspects highlight why understanding the exothermic nature of hydration is essential for concrete professionals.