Hydration

• A. A chemical reaction that causes cement to set
• B. The shrinkage of concrete as it cures
• C. The chemical process that causes concrete to harden
• D. The mixing of cement and water to form paste

Answer: (C)

Hydration is the chemical reaction between cement and water that causes concrete to harden, forming the binding hydration products that give the concrete its strength. This reaction creates compounds like calcium silicate hydrate and calcium hydroxide, which build a solid matrix that grips the aggregates together. The reason this is the best description is that it captures the essential, ongoing chemical process that leads to strength development over time, not just an initial stiffening.

Setting is connected to hydration but describes the early stiffening phase, while hardening refers to the continuing chemical reactions that increase strength. Shrinkage relates to dimensional changes during drying and curing, not the fundamental hardening reaction. Mixing cement and water to form paste is the preparation step that starts the hydration, but does not itself describe the chemical process that causes hardening.