---
title: "Concrete batching and mixing plants"
subject: "Construction Management"
chapter: 4
key: "semester_8/construction_management:concrete-batching-mixing-note"
source: https://www.bctengineer.com/q/semester_8/construction_management/concrete-batching-mixing-note
site: BCT Engineering
---

# Concrete batching and mixing plants

Construction Management · Chapter 4: Familiarization with Construction Equipments

- Asked in: 2071 Bhadra, 6 marks; 2070 Bhadra, 4 marks; 2067 Mangsir (old course), 4 marks; 2066 Magh (old course), 4 marks; 2075 Bhadra, 3 marks; 2065 Baisakh (old course); 2064 Poush (old course) (asked 7 times)
- Video: [Concrete Batching Plant|| CMD|| Concrete By Weight || NIAS](https://www.youtube.com/watch?v=VzLmifrRQ5A) — Civil Edu Aqeel
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/construction_management/concrete-batching-mixing-note
- Whole chapter: https://www.bctengineer.com/md/semester_8/construction_management/chapter-4

## Question

Write a short note on concrete batching and mixing plants (concrete mixers).

## Short answer

A batching plant accurately weighs cement, water, sand, aggregate and admixture; types include manual, semi-automatic and fully automatic. Mixers are batch, continuous or transit. Mixing takes 1.5-2 minutes; charge water, aggregate, cement, sand, then remaining water.

## Answer

#### Concrete batching plant
A batching plant measures the ingredients (cement, water, sand, aggregate, admixture) accurately in the proportions of the mix design. Accurate weigh-batching improves strength and uniformity.

Main parts: aggregate storage bins/hoppers, conveyor or skip hoist, cement silo and weigh hopper, water tank and meter, admixture dispenser and control panel.

Types: manual (volume) batching for small jobs; semi-automatic; fully automatic computer-controlled plants. Stationary or mobile plants.

#### Concrete mixers
```text
   Drum mixer (tilting)
        ____
      /  /\  \   charging ->
     |  |  |  |  rotating drum with
      \ \__/ /   blades inside
        ----     discharge by tilting
```
- **Batch mixers:** tilting drum (discharge by tilting, for large aggregate), non-tilting drum, reversing drum, pan (forced action), twin-shaft. Capacity: 0.1-3 m$^3$ per batch.
- **Continuous mixers** for large, steady output.
- **Transit mixers (ready-mix trucks)** carry and mix concrete from a central batching plant to the site.

#### Points
- Mixing time: normally 1.5-2 minutes for a drum mixer; at the correct drum speed.
- Charge in sequence: part of the water, aggregate, cement, sand, then remaining water.
- Wash the drum after use; mix at least until uniform colour and consistency.
- Machine mixing and batching give better quality, higher productivity and less labour than hand mixing, and are essential for large projects.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the main job of a concrete batching plant?
   A. To crush aggregate to size
   B. To transport concrete to the site
   C. To measure cement, water, sand, aggregate and admixture accurately in the mix-design proportions
   D. To compact concrete in the forms
   Answer: C. A batching plant weighs and measures the ingredients to the mix design, improving strength and uniformity. (Key point: Purpose of batching)

2. Which batch mixer discharges by tilting the drum and suits large aggregate?
   A. Pan mixer
   B. Twin-shaft mixer
   C. Tilting drum mixer
   D. Continuous mixer
   Answer: C. The tilting drum mixer discharges by tilting and is used for large aggregate. (Key point: Tilting drum mixer)

3. What is the function of a transit mixer (ready-mix truck)?
   A. Measure the ingredients at the plant
   B. Spray concrete on tunnel walls
   C. Level the finished slab
   D. Carry and mix concrete from a central batching plant to the site
   Answer: D. Transit mixers carry and mix concrete from the central batching plant to the site. (Key point: Role of transit mixers)

4. Which charging sequence is given for a drum mixer?
   A. All water first, then cement only
   B. Sand, cement, then dry aggregate with no water
   C. Cement, sand, aggregate, then all water
   D. Part of the water, aggregate, cement, sand, then remaining water
   Answer: D. Part of the water goes in first, then aggregate, cement and sand, then the remaining water. (Key point: Charging sequence)

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