The accumulation of water on the outer surface of freshly placed concrete is:
Correct Answer: B. Bleeding
📚 Detailed Explanation: Bleeding — Water Accumulation on Concrete Surface
Why B (Bleeding) is correct: Bleeding (also called water gain) is the specific concrete engineering term for the accumulation of water on the upper surface of freshly placed concrete. It is caused by the gravitational settlement of heavier particles (aggregate, cement) that push the lighter free water upward.
The Bleeding Process
| Step | What Happens |
|---|---|
| 1. Fresh concrete placed | Mix contains more free water than needed for hydration |
| 2. Settlement begins | Dense particles (aggregate ≈2650 kg/m³, cement ≈3150 kg/m³) settle under gravity |
| 3. Water displaced upward | Free water (1000 kg/m³) is pushed upward through capillary channels |
| 4. Surface film forms | Water + fine cement/sand particles appear at the top surface |
| 5. Water evaporates or is troweled | Laitance (weak paste layer) remains; capillary voids stay |
Why the Other Options Are Wrong
| Option | What It Actually Means |
|---|---|
| A. Transpiration | Loss of water vapour from plant leaves; not a concrete term |
| B. Bleeding | Water accumulation on concrete surface — correct answer |
| C. Guttation | Water exudation from plant tissues; not a concrete term |
| D. Ponding | A curing METHOD where water is deliberately pooled on hardened concrete; opposite concept |
- Bleeding = water gain: free water accumulates on the outer surface of freshly placed concrete.
- The water also contains dissolved fine cement and sand particles, forming laitance on evaporation.
- Calcium chloride addition and excessive troweling both increase the probability of bleeding.