Which term describes the chemical process that causes concrete to harden?

• A. Hydration
• B. P-Delta effect
• C. FF/FL ratio
• D. Joints

Answer: (A)

Hydration is the chemical process that causes concrete to harden. When cement and water mix, chemical reactions occur that form calcium silicate hydrate (C-S-H) and calcium hydroxide. The C-S-H gel develops a solid, interconnected matrix that binds the aggregate particles together, turning a workable mixture into a hard, strong material. The strength and durability grow as hydration products continue to form, especially with proper curing that keeps the mixture moist and at a suitable temperature. The other terms describe unrelated concepts: the P-Delta effect is a structural stability phenomenon due to additional bending moments from axial loads, joints are construction separations between pours, and FF/FL ratio refers to mix or design properties not about the chemical hardening process.