If the effective working time is 7 hours and per batch time of concrete is 3 minutes, the output of a concrete mixer of 150-litre capacity is (in litres):
Correct Answer: D. 18900
📚 Detailed Explanation: Concrete Mixer Output Calculation
Why D (18,900 litres) is correct: Concrete mixers do not operate at 100% efficiency for the full working period. Downtime for cleaning, adjustments, loading delays, and minor breakdowns reduces effective working time. A standard efficiency factor of 90% is applied in Indian engineering practice.
Gross working time = 7 hours = 420 minutes
Efficiency factor = 90% = 0.90
Effective working time = 420 × 0.90 = 378 minutes
Efficiency factor = 90% = 0.90
Effective working time = 420 × 0.90 = 378 minutes
Number of batches = 378 ÷ 3 = 126 batches
Output = 126 × 150 litres = 18,900 litres
Sensitivity to Efficiency Factor
| Efficiency Factor | Effective Time (min) | Batches | Output (L) |
|---|---|---|---|
| 100% (no downtime) | 420 | 140 | 21,000 |
| 90% (standard) | 378 | 126 | 18,900 |
| 75% | 315 | 105 | 15,750 |
- Standard efficiency factor for concrete mixers = 90%.
- Output = (Working time × efficiency ÷ batch time) × mixer capacity = 126 × 150 = 18,900 L.