The percentage of fly ash used in high volume fly ash concrete is:
Correct Answer: D. 50-60%
📚 Detailed Explanation: High Volume Fly Ash (HVFA) Concrete
Why D (50–60%) is correct: HVFA concrete is defined as concrete where fly ash replaces 50–60% (by mass) of the Portland cement cementitious content. This is the internationally recognised definition established by Malhotra and Mehta (CANMET/ACI). Options A (10–25%) = standard fly ash concrete (not “high volume”). Options B (70–80%) and C (>90%) exceed the standard HVFA definition and are experimental ultra-HVFA mixes not in standard usage.
Fly Ash Replacement Levels
| Category | Fly Ash Replacement (%) |
|---|---|
| Standard fly ash concrete | 15–30% |
| High Volume Fly Ash (HVFA) | 50–60% |
| Ultra-HVFA (experimental) | 60–80% |
- HVFA concrete = 50–60% fly ash by mass of total cementitious material.
- HVFA benefits: 50% reduction in CO₂, lower heat of hydration, improved long-term durability, reduced permeability.