Efflorescence of concrete appears as:
Correct Answer: B. White fluffy layers on the concrete surface
📚 Detailed Explanation: Efflorescence — White Deposits on Concrete Surface
Why B (White fluffy layers) is correct: Efflorescence is defined as the deposition of white, powdery, or crystalline material on the surface of concrete or masonry. It forms when water percolates through concrete, dissolves soluble calcium hydroxide [Ca(OH)2], and carries it to the surface. There, it reacts with atmospheric carbon dioxide to form calcium carbonate (CaCO3), which appears as white fluffy or crystalline layers.
Mechanism of Efflorescence Formation
| Step | Process | Chemistry |
|---|---|---|
| 1. Water ingress | Rain, groundwater, or moisture penetrates concrete | H2O dissolves soluble Ca(OH)2 |
| 2. Internal transport | Water carries calcium salts (CaSO4, Ca(OH)2) through capillary pores to the surface | Capillary suction drives transport |
| 3. Surface deposition | Water evaporates at the surface; leaves dissolved salts behind | Ca(OH)2 deposits directly, or reacts: Ca(OH)2 + CO2 → CaCO3 + H2O |
| 4. White layer forms | CaCO3 is insoluble, white, and forms crystalline or fluffy deposits | White efflorescence visible |
Prevention and Remediation
| Strategy | Method |
|---|---|
| Reduce permeability | Low w/c ratio; dense, well-compacted concrete; silica fume additions |
| Waterproof coatings | Apply sealants/waterproof membranes to prevent water ingress |
| Proper drainage | Ensure water does not pond against concrete surfaces |
| Removal (mild) | Wire brushing; dilute hydrochloric acid wash (1:10); then neutralise and rinse |
Why Other Options Are Wrong
| Option | What It Actually Represents |
|---|---|
| A. Rust stains | Corrosion of reinforcement steel; not efflorescence |
| B. White fluffy layers | Correct — CaCO3 / Ca(OH)2 deposits = efflorescence |
| C. Dark moisture patches | Dampness or water absorption; not efflorescence |
| D. Surface cracks from ASR | Alkali-Silica Reaction causes gel expansion and map cracking; not efflorescence |
- Efflorescence = white fluffy or crystalline deposits on concrete surface.
- Chemical cause: Ca(OH)2 + CO2 → CaCO3 (white) + H2O
- Efflorescence is primarily aesthetic but indicates water percolation, which signals a durability concern.