Concrete Cube Casting Procedure as per IS 516:2018 & IS 456:2000 – Complete Site Guide:

• Concrete cube casting is a crucial quality control activity on construction sites. Its goal is to assess the compressive strength of concrete and confirm that the supplied material meets the specified design criteria.
• The cube test enables engineers to check the quality of concrete used in structural elements such as columns, beams, slabs, footings, and retaining walls. The results ensure compliance with IS 456:2000 and IS 516:2018 standards.
• Typically, concrete cubes are tested after 7 and 28 days of curing. The 7-day test indicates early strength development, while the 28-day test serves as the standard for concrete acceptance.

Apparatus Required for Concrete Cube Casting

The following apparatus should be available before starting cube casting operations, and all equipment to be used should be clean and in good condition to avoid inaccurate test results.:

• Cube moulds ( Size 150mm×150mm×150mm )
• Tamping Rod 16mm dia & 600mm long
• Sampling Tray
• Trowel
• Mould oil or release agent
• Identification tags or a permanent marker
• Water Curing tank
• Compression Testing Machine (CTM)
• Personal protective equipment (PPE)

The procedure of the test:

Step 1: Sampling of Fresh Concrete

Proper sampling is to be done because the concrete cube represents the whole structure or structural member for which concrete is being placed.

Procedure

1. Collect the sample from the discharge point of the transit mixer or batching plant.
2. Avoid collecting concrete from the first or last portion of discharge.
3. Take samples from different portions of the batch.
4. Combine the samples and remix thoroughly to obtain a representative sample.
5. Perform slump testing before cube casting.

Important Precautions

• Do not add extra water to the sample.
• Cube casting should begin immediately after sampling.
• Protect the sample from direct sunlight and excessive evaporation.

Step 2: Preparation of Cube Mould

Before casting concrete cubes, ensure that the cube moulds are properly prepared.

Procedure

1. Clean all internal surfaces of the mould.
2. Remove old concrete particles and dust.
3. Assemble the mould correctly.
4. Tighten all bolts securely.
5. Check that there are no gaps through which slurry can leak.
6. Apply a thin layer of mould oil on all internal faces.

Inspection Checklist

✓ Mould dimensions to be verified

✓ Bolts tightened

✓ Internal surfaces clean

✓ Mould oil applied uniformly

✓ Identification number available

Improper mould preparation may lead to honeycombing, edge damage, and inaccurate test results.

Step 3: Filling the Cube Mould

The concrete ordered for the structure is generally delivered via Transit Mixtures (TM). Collect the concrete sample from the transit mixture and fill the concrete in the prepared cube mould in layers to ensure proper compaction.

Procedure

Fill the mould in three approximately equal layers.

First Layer

1. Place the first layer up to one-third of the mould depth.
2. Compact the layer using 35 strokes of the tamping rod.
3. Distribute the strokes uniformly throughout the surface.

Second Layer

1. Place the second layer carefully.
2. Compact with another 35 strokes.
3. Allow the rod to penetrate slightly into the previous layer.

Third Layer

1. Fill the mould completely.
2. Compact with 35 strokes.
3. Ensure complete compaction without segregation.

Total Strokes

35 strokes × 3 layers = 105 strokes per cube

Proper compaction removes entrapped air and improves the accuracy of compressive strength results.

Step 4: Surface Finishing

After compaction:

1. Add additional concrete if settlement occurs.
2. Strike off excess concrete using a trowel.
3. Finish the concrete surface level with the top of the mould.
4. Produce a smooth and uniform finish.

The top surface should be free from depressions, cracks, and voids.

Step 5: Identification and Marking

Immediately after casting, do the following:

• Mark cube number.
• Record grade of concrete.
• Mention the location of concreting.
• Record casting date.
• Record batch number if available.

Example Identification

M35-C1-10/06/2026

Where:

• M35 = Grade of concrete
• C1 = Cube Number
• 10/06/2026 = Date of Casting 

Proper identification prevents confusion during testing.

NOTE:

• The required number of cubes to be cast for a particular structure depends upon the quantity of concrete required for the structure, and  as per the IS456 Codal provision, the number of concrete cubes to be cast is given below:
  

  Quantity of Concrete in the Work (Cum)	Number of Samples
  1-5	1 set
  6-15	2 sets
  16-30	3 sets
  31-50	4sets
  51 and above	4 + one additional sample for each additional 50cum or part thereof

Step 6: Initial Storage of Cubes

After casting:

1. Keep cubes in a vibration-free area.
2. Protect them from direct sunlight.
3. Prevent moisture loss by covering a wet heassian cloth.
4. Maintain temperature between 22°C and 32°C if possible.

Storage Duration

24 ± 0.5 hours

Disturbing cubes during this period can damage the cube internally and may affect strength results.

Step 7: Demoulding of Cubes

After approximately 24 hours:

1. Remove the mould carefully.
2. Avoid damaging cube edges.
3. Inspect for cracks or honeycombing.
4. Verify identification markings.

Any damaged cube should be rejected and recorded.

Step 8: Curing of Cubes

Immediately after demoulding:

1. Immerse cubes completely in clean water in the curing pond.
2. Maintain continuous curing until testing.
3. Ensure cubes do not touch each other.
4. Maintain adequate water level throughout the curing period.

Curing Duration

• 7 Days Cube
• 28 Days Cube

Proper curing significantly influences the development of the cube’s compressive strength.

Step 9: Compression Testing of Cubes

The compressive strength test is performed using a Compression Testing Machine (CTM).

Procedure

1. Remove the cube from the curing pond.
2. Clean the surface moisture of the concrete cubes.
3. Measure dimensions if required.
4. Place the cube centrally on the compressive testing machine platen.
5. Apply load gradually without shock.
6. Continue loading until failure occurs.
7. Record maximum load.

Calculation of Compressive Strength

The compressive strength of concrete is calculated by dividing the Maximum/failure load by the loaded area of the cube.

For a standard 150 mmx150mmx150mm concrete cube:

The Loaded Area = 150 × 150 = 22,500 mm²

For Example:

Assume the maximum load at which the cube fails is known as the Failure Load = 900 kN

The Compressive Strength of the concrete cube = 900,000 ÷ 22,500

Compressive Strength = 40 MPa

Record the result for each cube separately and calculate the average strength.

Acceptance Criteria as per IS 456:2000

Concrete is considered acceptable when:

1. The average strength of test specimens is greater than the characteristic strength plus the required margin.
2. No individual test result falls below the specified limits given in IS 456.

If results do not satisfy acceptance criteria:

• Review batching records.
• Verify curing practices.
• Conduct additional investigations.
• Consider core testing if necessary.

Common Mistakes During Cube Casting

Many cube failures result from poor site practices rather than poor concrete quality.

Common Errors

• Dirty cube moulds
• Improper mould oil application
• Inadequate compaction
• Excessive vibration
• Delayed casting
• Wrong identification
• Early demoulding
• Insufficient curing
• Improper CTM loading

Avoiding these mistakes improves the reliability of test results.

Site Engineer’s Checklist Before Cube Casting

✓ Slump test completed

✓ Cube moulds cleaned

✓ Mould oil applied

✓ Identification labels ready

✓ Tamping rod available

✓ Sampling completed correctly

✓ Cube register prepared

✓ Curing tank available

✓ Test schedule prepared

Frequently Asked Questions

Q1. Why are six cubes generally cast?

Answer: Six cubes are commonly cast so that three cubes can be tested at 7 days and three cubes at 28 days.

Q2. Why is the 28-day cube strength important?

Answer: Concrete reaches most of its design strength by 28 days, making 28 days the standard acceptance age.

Q3. What is the standard cube size in India?

Answer: The standard concrete cube size is 150 mm × 150 mm × 150 mm.

Q4. What happens if a cube fails?

Answer: The engineer investigates the cause, reviews quality records, and may order additional testing, such as core testing. If it fails, then the structural member may be demolished and recast. For this, the engineer in charge has to make a decision.

Q5. How many strokes are required for cube compaction?

Answer: A total of 105 strokes is applied, consisting of 35 strokes for each of the three equal layers.

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