The slump test is the most widely used field test for assessing the workability and consistency of fresh concrete. It provides a simple, quick indication of concrete's flow characteristics and helps ensure the mix is suitable for placement. Proper workability is essential for achieving complete compaction and full strength in the hardened concrete.
Understanding Concrete Workability
Workability refers to how easily concrete can be mixed, placed, compacted, and finished without segregation. It's influenced by water content, aggregate properties, cement type, and admixtures. The slump test measures the consistency of concrete by observing how much a molded cone of concrete slumps when the mold is removed.
Slump Test Procedure
The test uses a standard truncated cone (slump cone) 300mm high. Fresh concrete is placed in three equal layers, each tamped 25 times with a steel rod. After filling and leveling, the cone is lifted vertically, and the slump is measured as the vertical drop from the original height to the displaced center of the concrete.
- Fill cone in three equal layers of approximately 100mm each
- Tamp each layer 25 times with 16mm diameter tamping rod
- Strike off excess concrete level with top of cone
- Lift cone vertically in 2-3 seconds without lateral movement
- Measure vertical settlement to nearest 5mm
Slump Classification and Typical Values
Slump values range from 0-200mm+. Low slump (0-50mm) indicates dry, stiff concrete suitable for roads and pavements. Medium slump (50-100mm) is typical for foundations and mass concrete. High slump (100-180mm) is used for columns, beams, and reinforced sections requiring easier placement.
Common Issues and Troubleshooting
True slump shows uniform subsidence. A shear slump (concrete shears off) or collapse slump (complete breakdown) indicates issues with mix design, excessive water, or segregation. If results are outside specification, the batch should be rejected or adjusted with admixtures under engineer supervision.
Conclusion
Slump testing is a critical quality control measure that must be performed correctly for meaningful results. Our field technicians are trained to perform and interpret slump tests according to EN and ASTM standards. Contact us for on-site concrete testing services.
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- Flow Table Test
- Compressive Strength Testing
- Air Content Testing
Applicable Standards
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