The Slump Test is a simple and widely used field test to measure the consistency or workability of fresh concrete before it sets. It indicates how easily the concrete can flow and be placed.
🎯 Purpose of the Slump Test:
- To assess the workability of concrete.
- To check uniformity batch to batch.
- To ensure the concrete mix has the desired water-cement ratio.
- Used for quality control during construction.
🧰 Apparatus Required:
- Slump cone (Abrams cone): 300 mm height, 200 mm bottom diameter, 100 mm top diameter
- Tamping rod: 16 mm diameter, 600 mm long, rounded at one end
- Base plate: Flat, non-absorbent surface
- Measuring scale
- Scoop and trowel
🛠️ Test Procedure:
- Dampen the cone and place it on a level base plate.
- Fill the cone in 3 layers, each approx. 1/3rd of the cone height.
- Tamp each layer 25 times with the tamping rod using uniform pressure.
- After the third layer is tamped, strike off the top surface.
- Immediately lift the cone vertically and gently.
- Allow the concrete to subside (slump) under its own weight.
- Measure the slump as the vertical difference between the height of the cone and the top of the subsided concrete using a ruler.
📏 Types of Slump:
| Slump Type | Shape | Interpretation |
|---|---|---|
| True Slump | Vertically subsided | Acceptable; good consistency |
| Shear Slump | Concrete shears and slips | May indicate lack of cohesion |
| Collapse Slump | Concrete completely collapses | Too wet; high workability |
| Zero Slump | No subsidence | Very low workability (dry mix) |
📊 Typical Slump Values:
| Concrete Type | Slump Range (mm) |
|---|---|
| Mass concrete (e.g., footing) | 25 – 75 |
| Reinforced slabs, beams | 75 – 100 |
| Pumpable concrete | 100 – 150 |
| High workability/self-compacting | >150 mm (other tests preferred) |
✅ Advantages:
- Simple and quick
- No elaborate equipment required
- On-site control of concrete quality
⚠️ Limitations:
- Not reliable for very dry or very wet mixes
- Cannot measure cohesiveness or segregation
- Other tests like flow table, Vee Bee, or compacting factor may be needed for special concretes
Your Slump Test Checklist for Site Engineers / Technicians is ready in Word format: