The durability of concrete is adversely affected by which of the following?
Correct Answer: D. Both cider and vinegar
📚 Detailed Explanation: Cider and Vinegar Attack Concrete Durability
Why D (Both cider and vinegar) is correct: Cider and vinegar are both acidic. Acids attack hardened concrete by reacting with calcium hydroxide [Ca(OH)2] and calcium silicate hydrate (C-S-H gel) — the primary strength-giving hydration products. This dissolves the binding material and progressively weakens the concrete, reducing its service life and durability.
Chemical Attack Mechanism
| Substance | Active Agent | Reaction with Concrete | Effect |
|---|---|---|---|
| Cider (apple-based) | Malic acid, carbonic acid (pH ≈3–4) | Acid + Ca(OH)2 → calcium malate + water | Dissolves cement matrix; reduces strength |
| Vinegar (acetic acid, 4–8%) | CH3COOH (acetic acid, pH ≈2–3) | Acetic acid + Ca(OH)2 → calcium acetate + water | Very aggressive; dissolves Ca(OH)2; expands pores |
| Alcohol | Ethanol (C2H5OH, neutral pH ≈7) | No significant chemical reaction with cement hydration products | Minimal effect on durability under normal conditions |
Factors Affecting Concrete Durability
| Degradation Agent | Mechanism |
|---|---|
| Abrasion / wear | Surface erosion by mechanical action |
| Weathering (freeze-thaw) | Water expansion on freezing causes spalling |
| Acids (cider, vinegar, industrial) | React with Ca(OH)2; dissolve cement paste |
| Sulfates | React with C3A → ettringite → expansion → cracking |
| Chlorides | Depassivate steel reinforcement → corrosion |
| CO2 (carbonation) | Converts Ca(OH)2 to CaCO3; lowers pH; depassivates steel |
- Cider and vinegar both reduce concrete durability through acid attack on the cement matrix.
- Alcohol has neutral pH and does not significantly attack hardened concrete.
- Durability is also reduced by abrasion, weathering, chemical gases, and physical attack.