What is the standard size of wood specimen for testing durability?
Testing Timber Durability: The "Graveyard" Test
The natural durability of timber is its inherent resistance to decay and insect attack without any preservative treatment. To classify different wood species, a standardized field test, often called a "graveyard test," is conducted. This test simulates real-world conditions where timber is in contact with the ground, which is the most severe environment for decay.
📝 Detailed Analysis of the Options
(a), (c), and (d)
These options represent incorrect dimensions for the standard durability test specimen. Using a non-standard size would lead to inconsistent results that could not be compared across different tests or species. Standardization is key to reliable material testing.
(b) 600×50×50 mm
This is the correct answer. The standard durability test, as proposed by the Forest Research Institute and reflected in Indian Standards, uses a wood specimen of size 600mm × 50mm × 50mm. The test procedure involves burying half of the specimen (300 mm) in the ground, leaving the other half exposed. The specimens are then inspected periodically over several years to assess the rate of decay or insect damage. The time it takes for the specimen to fail determines the timber's durability classification.
📊 Durability Classification Based on Test Results
Based on the performance in the graveyard test, timber is classified into three durability classes:
| Durability Class | Average Life in Graveyard Test |
|---|---|
| High Durability | More than 10 years |
| Medium Durability | 5 to 10 years |
| Low Durability | Less than 5 years |
💡 Study Tips
- Memorize the Dimensions: The standard size 600 × 50 × 50 mm is a key fact to remember for timber testing.
- Picture the Test: Visualize a 60 cm long wooden stake being hammered halfway into the ground. This helps to remember the purpose and method of the test.
- Link Test to Classification: Understand that the result of this specific test directly leads to the High (>10 years), Medium (5-10 years), and Low (<5 years) durability ratings.