Calcium chloride added in concrete acts as:
Correct Answer: D. Accelerator
📚 Detailed Explanation: Calcium Chloride = Accelerator
Why D (Accelerator) is correct: Calcium chloride (CaCl2) is the most widely used and most effective accelerating admixture for Portland cement concrete. It accelerates the hydration of C3S and C3A, reduces initial and final setting times, and increases the rate of early strength gain. All these effects define it as an accelerator.
CaCl2 is NOT the Other Types
| Option | Admixture Type | CaCl2 is this type? | Actual Examples |
|---|---|---|---|
| A. Air-entraining agent | Introduces micro-air bubbles; freeze-thaw resistance | NO | Vinsol resin, tallows, soaps, AEA surfactants |
| B. Plasticiser (water reducer) | Improves workability; reduces water demand | NO | Calcium lignosulphonate, naphthalene sulphonate, polycarboxylates |
| C. Retarder | Slows hydration; extends setting time | NO | Gypsum, sugar, starch, calcium lignosulphonate |
| D. Accelerator | Speeds hydration; reduces setting time; early strength | YES — CaCl2 is the standard accelerator | CaCl2, Na2CO3, silicates |
CaCl2 Dosage and Limits
| Dosage | Effect |
|---|---|
| 1–2% by wt. cement | Effective acceleration; acceptable for plain/reinforced concrete (subject to Cl¹¯ limits) |
| 2–4% by wt. cement | Strong acceleration; risk of flash set; corrosion risk increases |
| >4% by wt. cement | Detrimental: flash set, severe corrosion, strength reduction |
| Any amount in PSC | Prohibited: stress-corrosion cracking risk of high-tensile wires |
- CaCl2 = accelerator: most common, most effective; reduces setting time; promotes early strength.
- Maximum safe dose: 2% by weight of cement in reinforced concrete.
- Completely prohibited in pre-stressed concrete regardless of dose.