Question:
In a Slake Durability Index (SDI) test, a rock sample of 500 g undergoes two standard cycles of wetting and drying. The mass of the sample retained after the test is 400 g. The SDI of the sample, in %, is
In a Slake Durability Index (SDI) test, a rock sample of 500 g undergoes two standard cycles of wetting and drying. The mass of the sample retained after the test is 400 g. The SDI of the sample, in %, is
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SDI is the percentage of the original sample mass that remains after the wetting and drying cycles.
Updated On: Jul 27, 2026
- 10
- 40
- 20
- 80
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The Correct Option is D
Solution and Explanation
Step 1: Recall what the Slake Durability Index means.
The Slake Durability Index (SDI), from the Franklin slake durability test, tells us how well a rock resists breaking down when it is repeatedly wetted, dried and tumbled.
A sample of known dry mass is placed in a rotating drum with a 2 mm mesh, run through wetting and drying cycles, and the mass that stays on the mesh, meaning it did not slake away, is weighed again.
Step 2: Write the SDI formula.
\[ SDI = \frac{\text{mass retained after the test}}{\text{initial dry mass}} \times 100 \]
This ratio is simply the fraction of the original rock that survived the cycles, turned into a percentage.
Step 3: Put in the numbers.
The initial mass is 500 g and the mass retained after the two standard cycles is 400 g.
\[ SDI = \frac{400}{500} \times 100 = 80 \text{ percent} \]
A rock with an SDI of 80 percent or more is generally classed as highly durable, so this sample slakes only a little.
Options (A) 10, (B) 40 and (C) 20 would all mean the sample lost most of its mass, which is far more slaking than 400 g out of 500 g retained actually shows, so they are wrong.
Final Answer:
The SDI of the sample is 80 percent.
\[ \boxed{80\%} \]
The Slake Durability Index (SDI), from the Franklin slake durability test, tells us how well a rock resists breaking down when it is repeatedly wetted, dried and tumbled.
A sample of known dry mass is placed in a rotating drum with a 2 mm mesh, run through wetting and drying cycles, and the mass that stays on the mesh, meaning it did not slake away, is weighed again.
Step 2: Write the SDI formula.
\[ SDI = \frac{\text{mass retained after the test}}{\text{initial dry mass}} \times 100 \]
This ratio is simply the fraction of the original rock that survived the cycles, turned into a percentage.
Step 3: Put in the numbers.
The initial mass is 500 g and the mass retained after the two standard cycles is 400 g.
\[ SDI = \frac{400}{500} \times 100 = 80 \text{ percent} \]
A rock with an SDI of 80 percent or more is generally classed as highly durable, so this sample slakes only a little.
Options (A) 10, (B) 40 and (C) 20 would all mean the sample lost most of its mass, which is far more slaking than 400 g out of 500 g retained actually shows, so they are wrong.
Final Answer:
The SDI of the sample is 80 percent.
\[ \boxed{80\%} \]
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