Workability classification — what does a slump of about 6.5 cm indicate? A concrete mix measured by the slump test gives a slump of approximately 6.5 cm (65 mm). This mix is generally described as:

Introduction / Context:
The slump test provides a quick index of workability for normal concrete. Typical practice groups slump values into qualitative classes to guide placement methods and vibration effort.

Given Data / Assumptions:

• Standard slump cone test per code.
• Unrevised mix with no special additives that radically change rheology.
• Normal ambient temperature.

Concept / Approach:

Approximate classes: very low (0–25 mm), low (25–50 mm), medium/plastic (50–100 mm), and high (100–175 mm), acknowledging variations by specification. A slump of 65 mm falls in the medium or “plastic” category, suitable for normal reinforced sections with vibration.

Step-by-Step Solution:

Verification / Alternative check:

Pavement and building specifications often call 60–80 mm slump mixes “plastic” when vibration is available.

Why Other Options Are Wrong:

• “Dry” and “earth-moist” correspond to very low slumps well below 50 mm.
• “Semi-plastic” is not a standard class and suggests lower workability than 65 mm implies.

Common Pitfalls:

• Comparing slump values of different mix types (e.g., high-range water reducer mixes) without considering rheology.

Final Answer:

Plastic (medium workability).