Pick up the correct statement from the following
Correct Answer: D. All options are correct
📚 Detailed Explanation: Role of Cement Hydration in Concrete
This question tests basic knowledge of how cement paste transforms from a plastic material into hardened concrete through the process of hydration.
Why D (All options are correct) is correct:
Statement A — Hardening due to hydration: Cement hydration is a series of exothermic chemical reactions between cement compounds (C3S, C2S, C3A, C4AF) and water, producing calcium silicate hydrate (C-S-H gel) — the primary binding and strength-giving product. Without water (no hydration), cement never hardens.
Statement B — Cement binds aggregates: During hardening, the C-S-H gel and calcium hydroxide matrix grow around aggregate particles, mechanically interlocking and chemically bonding to them, creating the composite structure of concrete.
Statement C — Cement provides strength, durability, water tightness: The quality of the hydrated cement matrix directly controls all three properties: C-S-H gel provides strength, the dense matrix limits ion transport (durability), and interlocking gel crystals reduce permeability (water tightness).
Statement A — Hardening due to hydration: Cement hydration is a series of exothermic chemical reactions between cement compounds (C3S, C2S, C3A, C4AF) and water, producing calcium silicate hydrate (C-S-H gel) — the primary binding and strength-giving product. Without water (no hydration), cement never hardens.
Statement B — Cement binds aggregates: During hardening, the C-S-H gel and calcium hydroxide matrix grow around aggregate particles, mechanically interlocking and chemically bonding to them, creating the composite structure of concrete.
Statement C — Cement provides strength, durability, water tightness: The quality of the hydrated cement matrix directly controls all three properties: C-S-H gel provides strength, the dense matrix limits ion transport (durability), and interlocking gel crystals reduce permeability (water tightness).
Key Concepts for Students
- Hydration produces C-S-H gel (strength) + Ca(OH)² (calcium hydroxide) + heat.
- C-S-H gel fills pores, provides strength, and contributes to water tightness.
- Ca(OH)² maintains the high pH (~12.5) that passivates steel reinforcement against corrosion.