---
title: "Quality control at site; slump test"
subject: "Concrete Technology and Masonry Structure"
chapter: 3
key: "semester_5/concrete_technology_and_masonry_structure:qc-and-slump-test"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/qc-and-slump-test
site: BCT Engineering
---

# Quality control at site; slump test

Concrete Technology and Masonry Structure · Chapter 3: Mix design of concrete and property of green concrete

- Asked in: 2073 Shrawan, 6 marks
- Video: [Slump Test - Fresh Concrete Quality Control Tests pt 1](https://www.youtube.com/watch?v=PawPLgpjtEg) — Tyler Ley
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/qc-and-slump-test
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-3

## Question

How do you assure the quality control of concrete at site? Explain slump test in detail.

## Short answer

Quality control: test materials, weigh batching, fixed w/c, slump checks per batch, proper compaction and curing, cube testing (mean of 4 consecutive ≥ fck+0.825s, individual ≥ fck-4 MPa). Slump test: fill cone in 4 layers, 25 strokes each, lift, measure subsidence; true slump valid. Typical slump 25-75 mm.

## Answer

#### Quality control of concrete at site (IS 456 Clauses 15 and 16)
1. **Materials**: test the cement (IS 4031), aggregates (IS 2386: grading, bulking, moisture), water and admixtures before use; store them properly (cement off the ground, aggregates kept separate).
2. **Mix proportioning**: use a design mix with weigh batching; correct for moisture, bulking and absorption; keep the w/c fixed.
3. **Mixing and transport**: use mechanical mixers (mixing for at least 2 min); avoid segregation; place within the time allowed.
4. **Workability checks**: slump test on every batch or truck.
5. **Placing, compaction and curing**: proper compaction (vibrators), clean formwork, cover blocks, and curing for at least 7 days (10 days for PPC; IS 456 cl. 13.5.1).
6. **Sampling and strength tests**: 150 mm cubes, sampled as per IS 456 cl. 15.2.2 (1 sample for 1-5 m$^3$, 2 for 6-15 m$^3$, 3 for 16-30 m$^3$, and so on); each sample gives a test result equal to the average of 3 cubes, tested at 7 and 28 days. Acceptance by cl. 16.1 and Table 11 (for M20 and above): the mean of any 4 consecutive test results $\geq f_{ck} + 0.825 s$ (or $f_{ck} + 4$ N/mm$^2$, whichever is greater), and every individual test result $\geq f_{ck} - 4$ N/mm$^2$ ($f_{ck} - 3$ N/mm$^2$ for M15).
7. **Records**, supervision, and calibration of equipment; core tests or NDT (rebound hammer, UPV) in case of doubt.

#### Slump test in detail (IS 1199)
**Apparatus**: slump cone (bottom diameter 200 mm, top 100 mm, height 300 mm), 16 mm tamping rod 600 mm long, base plate, scale.

**Procedure**: place the cleaned, moistened cone on the base plate; fill it in four layers, each about one-quarter of the height; tamp each layer with 25 strokes of the rod; strike off the top; lift the cone vertically within 5-10 s; measure the subsidence (the slump) from the top of the mould to the highest point of the subsided concrete.

**Results**: true slump (valid), shear slump (repeat the test) and collapse slump (too wet).
**Typical slump values**: 25-75 mm for lightly reinforced sections, 50-100 mm for heavily reinforced sections. The test is quick, but not suitable for very dry or very wet mixes. A variation of more than ±25 mm from the design value indicates a change in water content or grading.

## Check yourself

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

1. How often should slump tests be done as workability control at site?
   A. Once a week
   B. Only at 28 days
   C. Only when cracks appear
   D. On every batch or truck
   Answer: D. Slump is checked on every batch/truck to detect changes in water or grading. (Key point: Slump check frequency)

2. Minimum curing period for ordinary concrete per the answer is
   A. 7 days
   B. 3 days
   C. 14 days
   D. 28 days
   Answer: A. IS 456 requires at least 7 days curing (10 days for PPC). (Key point: Curing period)

3. The acceptance criterion for strength is that mean of 4 cubes must be at least
   A. fck - 0.825 s
   B. fck + 0.825 s
   C. fck + 1.65 s
   D. fck + 4
   Answer: B. IS 456 cl. 16.1 needs mean >= fck + 0.825 s and each individual >= fck - 4 N/mm2. (Key point: Acceptance criterion)

4. A variation of more than 25 mm in slump from the design value indicates
   A. a faulty cube mould
   B. higher cement grade
   C. a change in water content or grading
   D. correct curing
   Answer: C. Large slump shifts point to altered water content or aggregate grading. (Key point: Slump variation)

## Related in Concrete Technology and Masonry Structure

- [Quality control of concrete at site](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aquality-control-at-site) — Concrete Technology and Masonry Structure, chapter 5, asked 11×
- [Workability and slump test procedure](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aslump-test-procedure) — Concrete Technology and Masonry Structure, chapter 3
- [Role and quality of water in concrete](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Awater-role-quality-impurities) — Concrete Technology and Masonry Structure, chapter 1, asked 3×

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