Concrete Cube Casting and Storage SOP

1. Purpose

To establish a standardized procedure for the preparation, casting, curing, and storage of concrete cube specimens for compressive strength testing, ensuring consistent testing results and compliance with IS 516:1959 and IS 456:2000 standards.

2. Scope

This SOP applies to all concrete cube sampling and testing activities carried out at construction sites, covering the entire process from sample collection to testing at 7, 14, and 28 days.

3. Responsibilities

QA/QC Engineer

Oversees the sampling and testing process and ensures compliance with quality standards

Lab Technician

Prepares, casts, and tests concrete cube specimens

Site Engineer

Coordinates concrete pours and facilitates sample collection

Document Controller

Maintains records of test results and prepares reports

4. Materials & Equipment

Cube Molds

Standard 150mm × 150mm × 150mm metal molds

Mold Oil

Release agent for easy demolding

Sampling Tools

Shovels, scoops, and containers for concrete sampling

Tamping Rod

16mm diameter, 600mm long steel rod

Rubber Mallet

For tapping mold sides during compaction

Finishing Tools

Trowels and floats for surface finishing

Curing Tank

Water tank with temperature control (27°C ± 2°C)

Compression Testing Machine

Calibrated machine capable of 3000 kN load

5. Procedure

1

Preparation Before Sampling

Prepare sampling plan according to the concrete pour schedule
Determine number of cubes required (minimum 3 cubes per test age)
Clean cube molds thoroughly and check for damage or deformation
Apply thin coating of mold oil to inner surfaces
Assemble molds ensuring all bolts are tightened securely
Verify all equipment is clean and ready for use

2

Concrete Sampling

Take samples at point of discharge for ready-mix concrete
For site-mixed concrete, sample from at least five different portions of the batch
Collect at least 1.5 times the volume needed for cube casting
Record batch details, time, location, and mix design information
Perform slump test on the same concrete sample
Transport sample to casting location immediately

3

Cube Casting

Place molds on level, rigid, non-absorbent surface
Fill molds in three equal layers (approximately 50mm each)
Compact each layer with 35 strokes of the tamping rod distributed uniformly
Tap sides of mold 10-15 times with rubber mallet after tamping each layer
After top layer compaction, strike off excess concrete using trowel
Smooth surface with minimum manipulation to achieve flat finish
Mark cubes with unique identification numbers and casting date

4

Initial Curing

Cover cast specimens with damp cloth or plastic sheet
Store at temperature of 27°C ± 2°C
Protect from vibration and jolting
Keep in molds for 24 ± 0.5 hours from time of addition of water to mix
Maintain specimens in a place free from vibration

5

Demolding

Remove cubes from molds carefully after 24 ± 0.5 hours
Use screwdriver or similar tool gently if needed to loosen sides
Avoid damaging edges or corners during demolding
Mark each cube with permanent identification (batch number, date, etc.)
Inspect cubes for defects (honeycombing, damaged edges)
Record any observed defects in the sample register

6

Standard Water Curing

Place demolded specimens in water curing tank immediately
Maintain water temperature at 27°C ± 2°C
Ensure complete immersion with at least 15cm water above specimens
Change water in curing tank every 7 days
Ensure cubes are not touching each other or sides of tank
Add lime (approximately 2g/liter) to prevent leaching of calcium
Keep specimens fully submerged until testing time

7

Specimen Handling for Testing

Remove specimens from curing tank at appropriate test age (7, 14, 28 days)
Wipe surface water and grit from specimens
Test within 2 hours of removal from curing tank
If testing is delayed, keep specimens covered with wet burlap or cloth
Measure and record dimensions of each cube before testing
Weigh each cube and record weight

8

Compression Testing

Check that testing machine is calibrated and functioning properly
Place cube centrally on the lower platen of testing machine
Ensure that load is applied to opposite cast faces of the cube
Apply load at rate of 140 kg/cm²/minute without shock
Record maximum load at which specimen fails
Note and document the type of failure pattern
Calculate compressive strength by dividing maximum load by cross-sectional area

9

Documentation & Reporting

Record all test results in designated format
Calculate average strength of specimens for each test age
Compare results with acceptance criteria as per IS 456:2000
Document any deviations from standard procedure
Prepare comprehensive test report with all relevant details
Submit results to site engineer and project manager

6. Quality Control

Verify mold dimensions match standard requirements (150mm × 150mm × 150mm)

Ensure consistent compaction method across all specimens

Maintain curing temperature within specified range (27°C ± 2°C)

Cross-check specimen identification markers before testing

Calibrate compression testing machine every 6 months

Validate test results by checking for abnormal failure patterns

7. Acceptance Criteria

7-Day Strength

Minimum 67% of specified 28-day characteristic strength

28-Day Strength

Should meet or exceed specified characteristic strength (fck)

Individual Variation

No individual result should be less than fck - 3 N/mm²

Group Criteria

Average of 4 consecutive test results ≥ fck + 0.825 × established standard deviation

8. Specimen Storage Requirements

Temperature Control

Maintain curing tank at 27°C ± 2°C with thermostatic control

Water Quality

Use clean, potable water free from contaminants

Identification System

Clear labeling system with batch details and testing dates

Protection

Guard against damage, vibration, and contamination

Record Keeping

Maintain log of environmental conditions and specimen details

Access Control

Restricted access to prevent unauthorized handling

9. Safety Precautions

Handle fresh concrete with rubber gloves to prevent skin irritation

Wear safety goggles when applying mold oil and handling chemicals

Use proper lifting techniques when handling cube specimens

Wear appropriate PPE during compression testing

Have eye wash station nearby when handling chemicals

10. Troubleshooting Common Issues

Low Strength Results

Check compaction technique, verify curing conditions, assess concrete mix proportions

Honeycombing in Cubes

Improve compaction, check for proper tamping, assess slump of concrete

Damaged Specimens

Improve demolding technique, handle with care, ensure proper initial curing

Irregular Failure Pattern

Check testing machine platens, ensure cube is centered, verify perpendicular faces

11. Professional Tips

Hot Weather Precautions

Shield specimens from direct sunlight, increase frequency of water level checking

Cold Weather Precautions

Use insulated curing tanks, monitor temperature more frequently

Consistent Sampling

Take samples from middle portion of batch, not from beginning or end

Test Planning

Cast extra cubes for high-risk concrete elements as backup specimens

12. Conclusion

Proper cube casting and curing is essential for accurate determination of concrete strength. Following this SOP ensures reliable and consistent test results that accurately represent the in-situ concrete quality. Always maintain proper documentation and adhere to the specified standard procedures for valid quality assurance.

13. References

IS 516:1959 - Method of Tests for Strength of Concrete

IS 456:2000 - Plain and Reinforced Concrete - Code of Practice

IS 1199:1959 - Methods of Sampling and Analysis of Concrete

Project Quality Assurance Plan

Concrete Cube Casting & Storage SOP