Building Construction Technology: Why Concrete Never Really Dries
How buildings are actually put together, from brick bonds and timber joints to foundations, facades, waterproofing and factory-made homes.
Try 3 questions
1. Why can concrete harden even when poured underwater?
- Water pressure squeezes the mix solid
- It sets by chemical reaction with water
- Added salts make it freeze in place
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Answer: It sets by chemical reaction with water
Cement hardens through hydration, a reaction that binds water into new crystals, so it does not need to dry out at all.
2. Why do builders keep freshly poured concrete damp for several days?
- The hardening reaction needs water to continue
- Damp concrete is easier to smooth and polish
- Wetting it washes away the excess cement
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Answer: The hardening reaction needs water to continue
If the surface dries too early, hydration stops there, leaving weaker, more porous concrete that is prone to shrinkage cracks.
3. In a simple concrete beam resting on two supports, why is the steel rebar placed near the bottom?
- Rebar near the top would rust in the rain
- The bottom is stretched, and concrete is weak in tension
- The bottom is squeezed, and steel resists squeezing
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Answer: The bottom is stretched, and concrete is weak in tension
Under load the beam sags, stretching its lower fibers; concrete cracks easily in tension, so steel is put where the pulling forces are.
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