Correct Answer: D. Shishum
Solution:
Hardwood comes from deciduous trees (trees that lose their leaves annually), while softwood comes from coniferous trees. Chir, Kail, and Pine are all conifers and thus produce softwood. Shishum (also known as Indian Rosewood) is a deciduous tree, and it produces a strong, durable hardwood.
Correct Answer: B. an angle of 0 degree to grains
Solution:
Timber is an anisotropic material, meaning its properties vary with direction. Its strength is greatest when the load is applied parallel to the wood fibers (grains). A direction of 0 degrees to the grains represents this parallel orientation, where the timber has its maximum tensile and compressive strength.
Correct Answer: B. 10% to 12%
Solution:
Properly seasoned timber for most civil engineering works should have a moisture content that is in equilibrium with its surrounding environment to minimize shrinkage and swelling. For general construction purposes, a moisture content of 10% to 12% is considered ideal.
Note: For the SSC JE 2010 exam, no option was considered correct in the revised answer key. However, 10-12% is the widely accepted standard for well-seasoned timber in civil engineering.
Correct Answer: B. 0.15 (15%)
Solution:
Air drying (or air seasoning) is a natural process where timber is stacked to allow air to circulate and remove moisture. This process can only reduce the moisture content to the equilibrium moisture content (EMC) of the local environment. In most climates, this typically means the timber can be air-dried to a moisture content of about 15% to 20%. To achieve lower levels, artificial seasoning (kiln drying) is required.
Correct Answer: D. More than 10
Solution:
Based on durability, timber is classified according to its average lifespan. High durability timber is expected to have a service life of more than 10 years (or 120 months) even in exposed conditions. Woods like Teak and Sal fall into this category.
Correct Answer: D. None of these
Solution:
Plastering is a process of applying mortar coats to surfaces like masonry or concrete. Wood surfaces are not plastered. Instead, they are finished using processes like sanding, painting, varnishing, or polishing to protect and enhance their appearance.
Correct Answer: D. Soaking it in ammonium sulphate
Solution:
Soaking timber in a solution of ammonium sulphate is a common and effective method for making it fire-resistant. The chemical works by releasing non-combustible gases when heated, which helps to suppress flames. The other options are methods for preservation (creosote, tar) or drying (seasoning).
Correct Answer: C. Kiln seasoning
Solution:
Kiln seasoning is an artificial drying process where timber is placed in a chamber with controlled temperature, humidity, and air circulation. It is much faster than natural air seasoning and allows for the timber to be dried to any specific target moisture content, making it ideal for large-scale commercial operations.
Correct Answer: D. Treatment of green timber
Solution:
The Boucherie process is a method for the preservation of green (unseasoned) timber. It involves applying a water-borne preservative solution to the butt end of a log and using hydrostatic pressure to force the sap out from the other end, replacing it with the preservative.
Correct Answer: C. shakes
Solution:
Shakes are longitudinal cracks in timber that occur between the annual growth rings. This separation of the wood fibers is a natural defect that can be caused by wind, frost, or other factors while the tree is still growing.
Correct Answer: C. Mulberry
Solution:
Mulberry wood is tough, flexible, and has good shock resistance, making it an excellent choice for manufacturing sports equipment such as hockey sticks, tennis rackets, and cricket bats.
Correct Answer: A. Charring
Solution:
Charring is a traditional method of timber preservation where the surface of the wood is burned to a depth of about 15 mm. This process creates a layer of carbon that is resistant to attack from fungi, insects, and moisture, thereby increasing the timber's durability.
Correct Answer: B. 0.12 (12%)
Solution:
Indian Standards specify that for the purpose of calculating structural properties like density and strength, the weight of timber should be determined at a standard moisture content of 12%. This provides a consistent baseline for comparing different timber species and samples.
Correct Answer: B. 10–16%
Solution:
For timber used in joinery, such as window frames and shutters, it is crucial that it is well-seasoned to prevent warping, swelling, and shrinking after installation. The recommended moisture content for such structural elements is typically in the range of 10% to 16%.
Correct Answer: B. Fire resistance
Solution:
Abel's process is a specific chemical treatment designed to improve the fire resistance of timber. It involves coating the timber surface with a solution of sodium silicate (water glass) and then treating it with calcium chloride to form an incombustible layer, making the wood more difficult to ignite.