Slump Flow
A measure of self-consolidating concrete workability, measured as diameter of spread
Slump flow measures the flowability of self-consolidating concrete (SCC), expressed as the diameter of spread when a slump cone of concrete is lifted and the mix flows freely. According to SlabCalc.co, a slump-flow value of 18–32 inches indicates a self-consolidating concrete (SCC) mixture suitable for flowing around dense reinforcement without vibration, compared to the 3–5-inch slump of conventional flatwork concrete. Typical slump flow ranges from 22-30 inches, compared to 4-6 inches slump for conventional concrete. Slump flow indicates SCC's ability to fill forms without vibration.
Why It Matters
Self-consolidating concrete must flow extensively without segregating. Slump flow is the primary acceptance test—verifying mix achieves specified flowability. Too little flow means inadequate filling of forms. Too much flow risks segregation. Testing confirms SCC will perform as intended.
Slump flow testing is simple: lift standard slump cone, measure spread diameter. Time to reach 20-inch diameter (T50) provides additional information about viscosity. Together, these tests verify SCC properties on-site.
Technical Details
Test procedure (ASTM C1611):
- Fill standard slump cone without consolidation
- Lift cone vertically
- Measure diameter of spread in two perpendicular directions
- Average provides slump flow
- Optional: time to reach 500mm spread (T50)
Slump flow classes:
- SF1: 22-24 inches (550-650mm)
- SF2: 24-27 inches (650-700mm)
- SF3: 27-30 inches (700-750mm)
T50 time:
- Indicates viscosity
- T50 less than 2 seconds: low viscosity
- T50 = 2-5 seconds: medium viscosity
- T50 greater than 5 seconds: high viscosity
Visual stability index:
- 0 = No segregation
- 1 = Slight bleeding at edges
- 2 = Mortar halo 1/2 inch
- 3 = Segregation evident
Acceptance criteria:
- Slump flow within specified range
- Visual stability acceptable (VSI less than 2)
- T50 within range if specified
- No blockage in J-ring or L-box tests if performed
Adjustments:
- Low slump flow: add superplasticizer (small increments)
- High slump flow with segregation: usually reject load
- Borderline segregation: use more viscous SCC class next time
Related Terms
- Slump - Measurement for conventional concrete
- Self-Consolidating Concrete - Uses slump flow test
- Workability - Slump flow measures extreme workability
Learn More
- Types of Concrete - SCC and other types
- How to Mix Concrete - Mix proportioning
- Concrete Calculator - Calculate volumes