Slump Test Procedure – number of roddings per layer In the standard slump test, each of the three layers placed into the cone is compacted with a 16 mm diameter, about 60 cm long steel tamping rod. How many uniform roddings are applied to each layer?

Introduction / Context:
The slump test must follow a consistent procedure to yield comparable workability results. One crucial element is the number of tamping strokes (roddings) applied to compact each layer uniformly without overworking or segregating the mix.

Given Data / Assumptions:

• Standard Abrams cone, three equal layers by volume.
• Rod diameter ≈ 16 mm; rod length ≈ 60 cm with rounded ends.
• Level, non-absorbent base plate and immediate measurement after lifting the cone vertically.

Concept / Approach:

Most standards specify 25 uniform roddings per layer to achieve repeatable compaction within the cone. Fewer strokes may leave large voids, while more strokes can over-compact or cause segregation, making results less representative of field placement conditions.

Step-by-Step Solution:

Verification / Alternative check:

Training manuals and codes list “25 strokes per layer” as a key procedural parameter for the slump test.

Why Other Options Are Wrong:

20 or 30 strokes deviate from the standard and can change measured slump; 40–50 strokes are excessive for this test method.

Common Pitfalls:

Uneven rodding pattern, not distributing strokes across the cross-section, or lifting the cone with a lateral motion—all of which reduce result reliability.

Final Answer:

25 times