Identify the INCORRECT statement regarding ready-mix concrete (RMC) made with ordinary Portland cement:
Correct Answer: A. RMC in bags needs hydration activator
📚 Detailed Explanation: Ready-Mix Concrete — No Hydration Activator Needed
Why A is INCORRECT: OPC (Ordinary Portland Cement) begins hydrating immediately upon contact with water through a spontaneous exothermic chemical reaction. No activator is needed or used. The idea of requiring a “hydration activator” applies only to specialty systems like alkali-activated cements (geopolymers), slag-based cements, or inhibited cement systems — not to standard OPC-based RMC.
Ready-Mix Concrete (RMC) — Key Facts
| Feature | Detail |
|---|---|
| Production | Batched at central plant; mixed in transit mixer or dry-batched and mixed on site |
| Transport | Transit mixer (drum rotates at slow agitation speed, 2–4 rpm) during transport |
| Delivery time | Must be discharged within 90 minutes of adding water (IS 4926) or 300 drum revolutions |
| Advantages | Consistent quality, speed of construction, eliminates on-site batching errors |
Checking All Statements
| Statement | Verdict |
|---|---|
| A. RMC bags need hydration activator | INCORRECT — OPC activates on contact with water, no activator needed |
| B. Mix design is tailor-made for contractor | Correct — RMC is customised to specific grade, slump, aggregate size |
| C. RMC increases construction speed | Correct — eliminates on-site batching time |
| D. Wet RMC transported by transit mixer | Correct — transit mixer is the standard delivery vehicle |
- OPC-based RMC does NOT require a hydration activator — statement A is the incorrect one.
- RMC must be placed within 90 minutes of water addition per IS 4926.