How many types of machine mixers of concrete are available?
Correct Answer: A. 2 (Batch and Continuous) — Note: Commission invalidated this question in the revised answer key
📚 Detailed Explanation: Types of Concrete Machine Mixers
⚠ Note: This question was invalidated by the examining commission in the revised answer key. The explanation below presents the accepted textbook classification.
Standard Classification — 2 Main Types: Most Indian civil engineering curricula (following IS 1791 and standard textbooks) classify machine mixers into two primary categories: Batch Mixers and Continuous Mixers.
Type 1: Batch Mixers
Batch mixers produce concrete in measured batches, one load at a time. They are the most common type for building construction.
| Sub-type | Description | Use |
|---|---|---|
| Tilting drum mixer | Drum tilts to discharge; blades inside mix concrete | General construction up to M25 |
| Non-tilting drum mixer | Drum axis horizontal; discharge via chute at one end | Larger batches; less common now |
| Reversing drum mixer | Drum reverses rotation to discharge | Wet mixes; good mixing action |
| Pan mixer (counter-current) | Star-shaped blades rotate in fixed pan | Stiff mixes; precast yards; ready mix |
| Transit mixer | Drum on truck; mixes during transport | RMC; long-distance delivery |
Type 2: Continuous Mixers
Continuous mixers receive ingredients continuously and produce a steady stream of concrete. Used for very large volume, continuous pour situations.
| Feature | Batch Mixer | Continuous Mixer |
|---|---|---|
| Output | Discrete batches | Continuous stream |
| Control | High (each batch checked) | Lower (ongoing calibration needed) |
| Applications | Buildings, bridges, general construction | Dams, tunnels, long road sections |
- Primary classification: 2 types — Batch Mixers and Continuous Mixers.
- Batch mixers have 5 sub-types: tilting drum, non-tilting drum, reversing drum, pan mixer, transit mixer.
- Commission invalidated this question, likely due to ambiguity over whether sub-types are counted as separate “types.”