Concrete Technology Notes for SSC JE Civil Engineering
Rahul Kumar
SSC Exam Expert & Content Editor
In this note
- 1.Ingredients of Concrete
- 2.Cement
- 3.Grades of Concrete and Nominal Mixes
- 4.Water-Cement Ratio
- 5.Workability and Its Tests
- 6.Defects in Fresh Concrete
- 7.Curing
- 8.Admixtures
- 9.Useful Formulas
- 10.Quick Tips
- 11.Quick Revision Points
- 12.Practice Questions With Answers
- 13.How to Practise This Chapter
- 14.Frequently Asked Questions
PDF Notes: Concrete Technology Notes for SSC JE Civil Engineering
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Concrete technology deals with the materials, the mixing, the testing and the curing of concrete. It is one of the high-scoring topics of the Civil Engineering paper in SSC JE, because the questions are based on facts and standard values. These concrete technology notes for SSC JE explain cement, aggregates, the water-cement ratio, the grades, the workability tests and curing in simple language with practice questions.
Ingredients of Concrete
| Ingredient | Role |
|---|---|
| Cement | Binding material that gives strength after reacting with water |
| Fine aggregate (sand) | Particles smaller than 4.75 mm; fills the gaps between coarse aggregates |
| Coarse aggregate | Particles larger than 4.75 mm; gives volume and strength |
| Water | Starts the chemical reaction (hydration) and makes the mix workable |
| Admixtures | Chemicals added in small amounts to change some properties |
Cement
| Item | Detail |
|---|---|
| Common type | Ordinary Portland Cement (OPC) of grades 33, 43 and 53 |
| Main compounds | C3S (early strength), C2S (later strength), C3A (quick setting, heat), C4AF |
| Initial setting time (OPC) | Not less than 30 minutes |
| Final setting time (OPC) | Not more than 600 minutes (10 hours) |
| Soundness test | Le Chatelier apparatus |
| Gypsum | Added to control the setting of cement |
| Other cements | Portland Pozzolana Cement (PPC), Rapid Hardening Cement, Sulphate Resisting Cement, Portland Slag Cement |
Grades of Concrete and Nominal Mixes
| Grade | Mix ratio (cement : sand : aggregate) | Use |
|---|---|---|
| M5 | 1 : 5 : 10 | Plain concrete under foundations |
| M10 | 1 : 3 : 6 | Levelling course, plain cement concrete |
| M15 | 1 : 2 : 4 | Plain concrete work |
| M20 | 1 : 1.5 : 3 | Reinforced concrete (RCC) in general |
| M25 | 1 : 1 : 2 | RCC under moderate exposure |
- In the grade M20, M means mix and 20 is the characteristic compressive strength of 20 N/mm² at 28 days.
- Characteristic strength is the value below which not more than 5 per cent of the test results are expected to fall.
- The standard test specimen is a 150 mm cube.
Water-Cement Ratio
- The water-cement (w/c) ratio is the weight of water divided by the weight of cement.
- According to Abrams' law, the strength of concrete is inversely proportional to the w/c ratio; a lower ratio gives higher strength.
- Too much water makes the concrete weak and porous, and too little water makes it difficult to compact.
- About 0.38 of the weight of cement is needed as water for the full hydration of cement.
Workability and Its Tests
| Test | Used for | Point |
|---|---|---|
| Slump test | Plastic concrete of medium to high workability | Slump cone is 300 mm high; measures the drop (slump) of concrete |
| Compaction factor test | Low workability concrete | Value is close to 0.85 for low, 0.92 for medium and 0.95 for high workability |
| Vee-Bee test | Very dry concrete | Measures the time to change the shape of the cone into a cylinder |
| Flow table test | Highly workable concrete | Measures the spread of the concrete |
Defects in Fresh Concrete
- Segregation: separation of coarse aggregate from mortar.
- Bleeding: rise of water to the surface of fresh concrete.
- Honeycombing: empty spaces in hardened concrete because of poor compaction.
Curing
- Curing means keeping the concrete moist and warm for some days for proper hydration of cement.
- Concrete made with OPC should be cured for at least 7 days, and for at least 10 days when other cements or admixtures are used or in hot weather.
- The strength at 7 days is about 65 to 70 per cent of the 28-day strength.
- Methods of curing: ponding, wet gunny bags, spraying water and curing compounds.
Admixtures
| Admixture | Effect |
|---|---|
| Plasticiser and superplasticiser | Improve workability or reduce water |
| Retarder | Slows the setting; useful in hot weather |
| Accelerator | Speeds up the setting and early strength |
| Air-entraining agent | Adds tiny air bubbles for resistance to freezing |
Useful Formulas
| Property | Formula (fck in N/mm²) |
|---|---|
| Modulus of elasticity of concrete | Ec = 5000 √fck N/mm² |
| Flexural strength | fcr = 0.7 √fck N/mm² |
| Cylinder strength | About 0.8 times the cube strength |
Quick Tips
- Memorise the grades with the mix ratios, especially M10, M15, M20 and M25.
- Remember the initial and final setting time of OPC: 30 minutes and 600 minutes.
- Link the slump test with medium workability and the compaction factor test with low workability.
- Learn that the lower w/c ratio gives higher strength (Abrams' law).
Quick Revision Points
- M20 concrete has the mix 1 : 1.5 : 3 and a strength of 20 N/mm².
- Initial setting time of OPC is 30 minutes, and the final is 600 minutes.
- Strength is inversely related to the w/c ratio.
- Curing is needed for at least 7 days for OPC concrete.
- Ec = 5000 √fck.
Practice Questions With Answers
- What is the mix ratio of M20 concrete?
Answer: 1 : 1.5 : 3 - What does 20 in M20 mean?
Answer: Characteristic compressive strength of 20 N/mm² at 28 days - What is the standard size of the cube for the strength test?
Answer: 150 mm cube - Which test is used to find the workability of concrete with medium workability?
Answer: Slump test - What is the minimum initial setting time of OPC?
Answer: 30 minutes - Which law relates strength of concrete to the w/c ratio?
Answer: Abrams' law - What is the separation of coarse aggregate from mortar called?
Answer: Segregation - What is the minimum curing period for OPC concrete?
Answer: 7 days - What is the value of Ec for fck = 25 N/mm²?
Answer: 25,000 N/mm² (5000 × 5) - Which material is added to cement to control setting?
Answer: Gypsum
How to Practise This Chapter
Make a table of grades, mixes and tests and revise it every week. Then solve questions from our practice papers, the free SSC quizzes and the previous year papers page. Read the previous chapter, Surveying, and see all topics on the SSC JE Civil Engineering notes page. You can also compare the other branches: Mechanical and Electrical.
Frequently Asked Questions
What is concrete?
Concrete is a mixture of cement, sand, coarse aggregate and water, which hardens after some time and becomes strong.
What are the ingredients of concrete?
The ingredients are cement, fine aggregate, coarse aggregate and water. Admixtures are added sometimes.
What does M20 mean?
M20 means a mix with a characteristic compressive strength of 20 N/mm² at 28 days, and the nominal mix is 1 : 1.5 : 3.
What is the water-cement ratio?
It is the ratio of the weight of water to the weight of cement in the concrete mix.
What is Abrams' law?
It says that the strength of concrete is inversely proportional to the water-cement ratio.
What is the slump test?
The slump test measures the workability of fresh concrete by finding how much the concrete cone settles after the mould is removed.
What is curing of concrete?
Curing is keeping the concrete moist for some days so that the cement reacts properly and the concrete gains strength.
What is segregation of concrete?
Segregation is the separation of the coarse aggregate from the mortar in fresh concrete.
What are admixtures?
Admixtures are chemicals added in small amounts to concrete to change its properties, such as workability or setting time.
What is the setting time of OPC?
The initial setting time is not less than 30 minutes, and the final setting time is not more than 10 hours.
Is concrete technology important for SSC JE?
Yes. It is a high-scoring topic because many questions are direct facts and standard values.
How many questions come from concrete technology in SSC JE?
Usually three to five questions come from concrete technology, but the number changes from year to year.
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Surveying Notes for SSC JE Civil Engineering
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Rahul Kumar
SSC Exam Expert & Content Editor
Rahul is a senior SSC exam strategist with 8+ years of experience helping aspirants crack CGL, CHSL and MTS exams. He writes in-depth notification breakdowns, exam pattern guides and preparation strategies.