Addition of calcium chloride in concrete results in:
Correct Answer: B. Reduction in curing period
📚 Detailed Explanation: CaCl2 Reduces Curing Period by Accelerating Hardening
Why B (Reduction in curing period) is correct: Calcium chloride (CaCl2) is an accelerating admixture. It speeds up cement hydration, so concrete gains strength faster. Because strength is achieved sooner, the required curing period (the time concrete must be kept moist and protected to achieve its design strength) is reduced. Concrete can be put into service earlier, and formwork can be removed sooner.
Effects of CaCl2 on Concrete
| Effect | Correct? | Explanation |
|---|---|---|
| A. Increased ultimate strength | ✗ No | CaCl2 accelerates early strength but does not significantly increase the ultimate 28-day/90-day strength; may slightly reduce it at high doses |
| B. Reduction in curing period | ✓ Yes | Faster hydration = faster strength gain = shorter time to reach minimum required strength = reduced curing period |
| C. Retardation of moisture loss | ✗ No | CaCl2 accelerates hydration which consumes water faster; it does not retard moisture loss — that is the function of a curing compound |
| D. All of these | ✗ No | Only B is correct; A and C are wrong |
CaCl2: How It Works
| Mechanism | Detail |
|---|---|
| Accelerates C3S hydration | Ca2+ and Cl¹¯ ions increase the ionic strength of pore solution; accelerates dissolution of C3S and C3A |
| Increases rate of C-S-H formation | Faster gel formation; earlier strength gain |
| Reduces initial setting time | From ≈45–60 min (without) to ≈20–30 min (with 2% CaCl2) |
Practical Applications of CaCl2
| Application | Benefit |
|---|---|
| Cold weather concreting | Concrete gains strength before frost can damage it |
| Emergency repairs | Road/bridge repairs can be opened to traffic sooner |
| Precast concrete | Earlier demoulding; faster production cycle |
| Winter construction | Reduces heating requirements; concrete self-heats from accelerated hydration |
- CaCl2 → accelerated hydration → reduced curing period (concrete achieves required strength sooner).
- Safe limit: 2% by wt. of cement (limited by IS 456 chloride content rules).
- Banned in pre-stressed concrete; limited in reinforced concrete due to corrosion risk.