Concrete Cube Test – IS Code (IS 516 & IS 456), Procedure, Frequency & Acceptance Criteria
Concrete Cube Test – IS Code Quick Answer
- IS code for concrete cube test: IS 516:1959
- Cube casting, frequency & acceptance criteria: IS 456:2000
- Standard cube size: 150 × 150 × 150 mm
- Testing age: 7 days & 28 days
- Rate of loading: 140 kg/cm²/min
The concrete cube test is a fundamental quality control test used to verify whether the concrete supplied and placed at site meets the design compressive strength and complies with Indian Standards. It is one of the most reliable methods to assess the load-bearing capacity, durability, and uniformity of concrete used in structural elements such as slabs, beams, columns, footings, and foundations.
Carried out in accordance with IS 516:1959 and IS 456:2000, this test involves casting concrete into standard cube moulds, curing them under controlled conditions, and testing them under compression at specified ages—commonly 7 days and 28 days.
For site engineers, QA/QC teams, consultants, and contractors, the cube test is not just a routine activity—it is a critical checkpoint that confirms whether the structure is safe to proceed further.
Purpose of Concrete Cube Test in RCC Construction
The primary purpose of the concrete cube test is to confirm that concrete used in a structure can safely carry the loads for which it is designed. Since concrete primarily resists compressive forces, its compressive strength directly governs the safety and performance of RCC members.
The cube test helps to:
- Verify compliance with design grade of concrete
- Detect mixing, batching, or curing problems
- Ensure uniform quality of concrete
- Provide documented proof of structural safety
Concrete Cube Test IS Code (IS 516 & IS 456 Explained)
The concrete cube test is a standardized laboratory procedure used to determine the compressive strength of hardened concrete. In RCC construction, compressive strength is the most important mechanical property because concrete is primarily designed to resist compressive stresses.
- IS 516:1959 specifies the method of testing, including cube size, curing, loading rate, and testing procedure.
- IS 456:2000 defines sampling frequency, acceptance criteria, and quality control requirements for concrete used in structures.
Together, these two codes ensure that concrete used on site is safe, durable, and structurally reliable.
Standard Concrete Cube Test Size and Specifications
As per IS standards, the standard size of concrete cube used for compressive strength testing in India is:
- 150 mm × 150 mm × 150 mm
This size provides a representative volume of concrete and allows uniform stress distribution during testing.
Key Specifications
- Dimensions: 150 × 150 × 150 mm
- Dimensional tolerance: ±0.2 mm
- Mould material: Cast iron, steel, or rigid non-absorbent material
- Surface finish: Smooth interior faces
- Joint condition: Watertight to prevent leakage of cement slurry
Key Specifications:
- Cube dimensions: 150mm × 150mm × 150mm
- Tolerance: ±0.2mm on each dimension
- Surface finish: Smooth, non-absorbent material
- Mould material: Cast iron, steel, or high-grade plastic
- Joint sealing: Watertight to prevent mortar leakage
Materials and Tools Required for Concrete Cube Test
Accurate results in a concrete cube compressive strength test depend on the use of standardized equipment and proper material handling. Below is the complete list of essential tools and materials required for carrying out the test as per IS 516:1959 and IS 456:2000 guidelines.
Primary Equipment:
- Cube Moulds (150mm × 150mm × 150mm)
- Material: Cast iron or steel
- Surface: Machine-finished smooth interior
- Joints: Watertight assembly
- Quantity: Sufficient for planned testing frequency
- Tamping Rod
- Diameter: 16mm
- Length: 600mm
- Material: Steel with rounded ends
- Weight: Approximately 2kg
- Compression Testing Machine
- Capacity: Minimum 2000 kN
- Accuracy: ±1% of applied load
- Loading rate: 140 kg/cm²/minute
- Calibration: Annual certification required
Supporting Materials:
- Clean potable water for curing
- Mould release agent (light mineral oil)
- Vibrating table or needle vibrator
- Weighing balance (accuracy ±1g)
- Measuring cylinder for water
- Clean cloth for mould cleaning
- Permanent markers for identification
- Curing tank or wet burlap
- Steel float for surface finishing
Preparation and Cleaning Procedures
Mould Preparation:
- Clean all mould surfaces thoroughly with wire brush
- Remove any concrete residue or rust particles
- Apply thin layer of mould release agent
- Ensure all joints are tight and leak-proof
- Check dimensional accuracy with measuring tape
Equipment Calibration:
- Verify compression testing machine (CTM) calibration certificates
- Check tamping rod weight and dimensions
- Ensure weighing balance accuracy
- Test vibrating equipment functionality
Cube Test Procedure as per IS Code (Step-by-Step)
Phase 1: Concrete Sampling and Preparation
Concrete sampling is a critical step in cube testing. The objective is to ensure that test specimens accurately represent the concrete actually placed in the structure.
Sampling Guidelines (As per IS 456 & IS 516)
- Concrete samples shall be taken from fresh concrete at the point of placing, such as:
- Transit mixer discharge, or
- Pump delivery line during steady flow
- Sampling shall not be done from:
- The first discharge of the batch
- The last portion of the batch where segregation may occur
- The sample taken shall be representative of the entire batch
- Sampling and cube casting shall be carried out as soon as practicable after discharge
- During sampling and handling:
- Protect concrete from direct sunlight
- Avoid exposure to wind, rain, or drying
- Prevent loss of moisture before casting
Improper sampling is one of the most common reasons for misleading cube test results.
Cube Casting Procedure as per IS Code (Layer, Tamping & Vibration)
Step 1: Mould Preparation
- Place clean, oiled moulds on a level and rigid surface
Step 2: Concrete Placement
- Fill the mould in three approximately equal layers
Step 3: Compaction
- Manual compaction: 35 strokes per layer using tamping rod
- Mechanical compaction: 30–60 seconds per layer using vibrator
- Ensure full compaction without segregation
Step 4: Surface Finishing
- Strike off excess concrete
- Finish surface smoothly without adding water or cement paste
Curing Method and Duration as per IS Code
Initial Curing (First 24 Hours)
- Store cubes in a moist environment
- Maintain temperature close to 27 ± 2°C
Water Curing (After 24 Hours)
- Demould cubes after 24 hours
- Immerse completely in clean water
- Maintain curing water temperature at 27 ± 2°C
Curing Time Standards
- 7 days: Early strength assessment
- 28 days: Characteristic strength
- 56 / 90 days: Special or mass concrete
Testing Procedure and Machine Setup as per IS 516
- Remove cubes from curing tank and wipe surface moisture
- Measure cube dimensions
- Place cube centrally on CTM platen
- Apply load continuously and uniformly until failure
- Record maximum load and observe failure pattern
Rate of Loading for Concrete Cube Test as per IS 516
The standard rate of loading for concrete cube testing is:
140 kg/cm² per minute
Loading must be continuous and uniform. Incorrect loading rates can lead to false strength values and unreliable results.
Cube Test Frequency as per IS 456 (How Many Cubes?)
Cube test frequency ensures continuous monitoring of concrete quality.
General Practice (IS 456 Based)
- One sample = three cubes
- Minimum one sample per day or as directed by the Engineer-in-Charge
- Additional samples for:
- Important structural elements
- Large pours
- Suspected quality variation
Typical Frequency Table
| Concrete Quantity | Samples | Cubes per Sample |
|---|---|---|
| 1–5 m³ | 1 | 3 |
| 6–15 m³ | 2 | 3 |
| 16–30 m³ | 3 | 3 |
| 31–50 m³ | 4 | 3 |
| >50 m³ | +1 per 50 m³ | 3 |
How Many Cubes Are Taken in One Sample as per IS Code?
As per IS 456:2000:
- One concrete sample consists of three cubes
- All cubes are cast from the same batch
- Common testing practice:
- One cube tested at 7 days (optional)
- Two cubes tested at 28 days (average strength considered)
Acceptance Criteria for Cube Test as per IS 456
Individual Cube Strength
- No individual cube strength shall be less than 0.85 × characteristic strength
Average Strength
- Average strength of the sample shall be equal to or greater than characteristic strength
Example (M25 Concrete):
- Characteristic strength = 25 N/mm²
- Minimum individual cube strength = 21.25 N/mm²
7 Days and 28 Days Cube Strength as per IS Code
- 7-day strength generally achieves 65–70% of 28-day strength
- 28-day strength is used for acceptance and structural verification
Understanding Test Results and Calculations
Compressive Strength Formula
Compressive Strength = Maximum Load / Cross-sectional Area
Example
- Load = 675 kN
- Area = 22,500 mm²
- Strength = 30 N/mm² (PASS)
Common Reasons for Concrete Cube Test Failure
- Non-representative sampling
- Inadequate compaction
- Improper curing
- Incorrect loading rate
- Misaligned cube placement
Frequently Asked Questions (FAQs)
What is the concrete cube test?
The concrete cube test is a compressive strength test used to verify whether concrete placed in a structure meets the required design strength. Concrete cubes are cast from fresh concrete, cured under controlled conditions, and tested under compression as per IS 516:1959.
Which IS code is used for the concrete cube test?
IS 516:1959 – Specifies the procedure for testing concrete cubes, including casting, curing, and loading.
IS 456:2000 – Specifies sampling frequency, acceptance criteria, and quality control requirements for concrete used in structures.
Both codes are used together in practice.
Why is the concrete cube test important in RCC construction?
The cube test confirms whether the concrete used in RCC members such as beams, slabs, columns, and foundations can safely carry design loads. It helps detect issues related to mixing, batching, compaction, or curing before structural problems occur.
What is the standard size of a concrete cube as per IS code?
As per IS 516:1959, the standard concrete cube size used in India is:
150 mm × 150 mm × 150 mm
This size ensures uniform stress distribution and reliable compressive strength results for most structural concrete grades.
At what age is the concrete cube test conducted?
Concrete cube testing is commonly carried out at:
7 days – To assess early strength development
28 days – To determine the characteristic compressive strength
The 28-day strength is used for acceptance of concrete.
What is the rate of loading for the concrete cube test as per IS 516?
As per IS 516:1959, the standard rate of loading for concrete cube testing is:
140 kg/cm² per minute
The load must be applied continuously and uniformly until failure.
How many concrete cubes are taken in one sample as per IS code?
As per IS 456:2000:
One concrete sample consists of three cubes
All cubes are cast from the same batch of concrete
Common practice:
One cube tested at 7 days (optional)
Two cubes tested at 28 days (average strength considered)
What is the minimum frequency of concrete cube testing as per IS 456?
IS 456:2000 specifies that:
Concrete sampling shall be done at least once per day for each grade of concrete, or
As directed by the Engineer-in-Charge
Additional samples may be required for important structural elements, large pours, or suspected quality variations.
What is the acceptance criteria for concrete cube test results?
As per IS 456:2000:
No individual cube strength shall be less than 0.85 × characteristic strength
The average strength of the sample shall be not less than the characteristic strength, subject to IS provisions
What does 7-day cube strength indicate?
The 7-day cube strength indicates the early strength gain of concrete. Typically, it reaches about 65–70% of the 28-day strength and helps assess curing and early-age performance.
What should be done if concrete cube test results fail?
If cube test results do not meet acceptance criteria:
Review sampling, casting, and curing procedures
Conduct additional cube tests
Perform core testing if required
Assess structural safety with the structural engineer or consultant
Take corrective or strengthening measures if necessary
What are the common reasons for concrete cube test failure?
Common causes include:
Non-representative sampling
Inadequate compaction
Poor curing conditions
Incorrect loading rate during testing
Misalignment of cubes in the testing machine
Can a different cube size be used for high-strength concrete?
Yes. For high-strength concrete (above M50), 100 mm cubes or cylindrical specimens (150 mm diameter × 300 mm height) may be used. The testing method must comply with relevant standards and project specifications.
Is cube testing mandatory for all RCC works?
Yes. Cube testing is a mandatory quality control requirement for RCC works to ensure structural safety and compliance with IS codes.
What is the difference between cube test and cylinder test?
Cube test: Commonly used in India (IS standards)
Cylinder test: Commonly used in ASTM and international standards
Cube strength values are generally higher than cylinder strength values for the same concrete.
The concrete cube test is the most important quality control test in RCC construction. When carried out correctly as per IS 516 and IS 456, it ensures that concrete placed at site is structurally safe, durable, and compliant with design requirements.
Accurate sampling, proper compaction, controlled curing, and standardized testing are essential. Ultimately, the safety of a structure depends on concrete quality—and the cube test provides the final confirmation of that quality.
