Slump Test of Concrete: Procedure, Types of Slump and IS 1199

What is the Slump Test?

The slump test is the most widely used field test for measuring workability of fresh concrete. It is simple, quick, requires minimal equipment, and can be performed right at the construction site. Despite its simplicity, it provides a reliable measure of workability for normal concrete mixes (slump range 25–175 mm).

The test was developed in the United States around 1910 and is now standardized globally. In India, it is governed by IS 1199:1959 – Methods of Sampling and Analysis of Concrete. The apparatus used is called the Abrams Slump Cone (named after Prof. Duff Abrams who also gave us the W/C ratio law).

The basic principle is elegantly simple: fill a truncated cone with fresh concrete in layers, compact each layer, remove the cone, and measure how much the concrete “slumps” (subsides) under its own weight. Greater slump = greater workability.

Apparatus

The standard slump cone (Abrams Cone) specifications as per IS 1199:

• Top diameter: 100 mm
• Bottom diameter: 200 mm
• Height: 300 mm
• Material: 1.6 mm thick galvanized mild steel sheet
• Two handles welded to the sides for lifting; two foot pegs at base for standing on while filling

Other equipment needed: tamping rod (16 mm diameter, 600 mm long, bullet-nosed), measuring scale or ruler (graduated in mm), non-porous base plate, and a scoop for filling.

Procedure (IS 1199)

1. Clean and dampen the inside of the cone and the base plate. Place the cone on the flat, non-porous, damp base plate.
2. Stand on the foot pegs to hold the cone firmly in place throughout filling.
3. Fill the cone in three equal layers, each approximately one-third the volume. First layer ≈ 70 mm deep; second ≈ 160 mm; third to the top (300 mm).
4. Rod each layer 25 times with the tamping rod, distributing the strokes uniformly over the cross-section. For the second and third layers, the rod should penetrate through the layer into the layer below by approximately 25 mm.
5. Top off and strike off: After rodding the third layer, fill any deficiency and strike off flush with the top of the cone using the tamping rod.
6. Lift the cone vertically in 5–10 seconds by raising it steadily and carefully. Do not twist or move sideways. Place the cone beside the slumped concrete.
7. Measure the slump: Place the tamping rod horizontally across the top of the inverted cone (placed beside the slumped concrete) and measure the vertical distance from the bottom of the rod to the top of the slumped concrete at the highest point. This is the slump value in mm.
8. The entire test from start of filling to measurement must be completed within 5 minutes.

Types of Slump

After lifting the cone, the concrete can behave in three different ways:

1. True Slump (Acceptable)

The concrete subsides uniformly and symmetrically, retaining roughly the shape of the frustum but at a lower height. This is the ideal, valid result. The mix is cohesive and the slump measurement directly reflects workability. True slump occurs in well-proportioned, cohesive mixes.

2. Shear Slump (Not Acceptable — Repeat Required)

Half of the concrete cone slides diagonally off the other half, like a shear failure. This indicates a non-cohesive, poorly proportioned mix (often gap-graded aggregate or deficiency of fine particles). The test result is not considered valid — the test must be repeated with a fresh sample. If shear slump occurs repeatedly, the mix proportioning needs to be reviewed.

3. Collapse Slump (Indicates Over-Wet Mix)

The concrete completely collapses and spreads out flat. This indicates an excessively wet mix (very high W/C ratio, very high workability). The slump cannot be accurately measured. For such concretes, the Flow Table Test is more appropriate. Collapse slump concrete may be prone to severe segregation and bleeding.

Interpretation of Slump Values

Limitations of the Slump Test

The slump test, despite its ubiquity, has several well-known limitations:

• Not reliable for very stiff mixes (slump near zero — cannot differentiate between different very-low-workability mixes).
• Not valid for very wet mixes (collapse slump — concrete flows out).
• Does not measure cohesiveness or stability — two mixes with same slump can have very different tendency to bleed or segregate.
• Operator-dependent: Lifting speed, rodding technique, and leveling affect results. Always done by trained personnel.
• Not suitable for SCC, lean concrete, or dry-press concrete — specialized tests required.
• Gives a single number — does not characterize the full flow behavior of concrete.

🎯 Exam Tips (RTMNU)

✅ Key Takeaways

• Slump test: most common workability test; IS 1199; suitable for 25–175 mm range.
• Cone: Top 100 mm, Bottom 200 mm, Height 300 mm. Fill in 3 layers, rod 25 times each.
• Lift cone in 5–10 seconds; measure vertical subsidence from highest point.
• True slump = valid; Shear slump = repeat; Collapse slump = over-wet mix, use flow table test.
• Limitations: not for stiff mixes, wet mixes, or SCC; operator-sensitive; single-parameter test.

📖 Related Reading: Compaction Factor Test: Procedure and Calculation | Factors Affecting Workability

🔗 External Reference: IS 1199:1959 – Methods of Sampling and Analysis of Concrete (BIS)

❓ FAQs