JNTU
JNTU B.Tech II BUILDING MATERIAL CONSTRUCTION AND PLANNING Previous Question Paper (October - 2020 - R16)
Answer any five questions. All questions carry equal marks.
Main
With the help of a neat sketch, explain the working of Hoffman’s kiln for the burning of bricks.
Answer
Hoffman's kiln is a continuous type of kiln used for the large-scale burning of bricks. It operates on the principle of continuous firing, where the fire moves through the kiln while the bricks remain stationary, resulting in high thermal efficiency and fuel economy.
The kiln consists of a circular or oval tunnel divided into 12 or more chambers. Each chamber is connected to a central chimney through a flue and has an opening for loading and unloading bricks. The process follows a continuous cycle of preheating, burning, and cooling:
- Loading and Unloading: While one chamber is being loaded with raw bricks, another is being unloaded with burnt bricks.
- Preheating: Air entering the kiln passes through chambers containing recently burnt bricks, absorbing their heat. This preheated air then enters the chamber currently being fired, significantly reducing fuel consumption.
- Burning: Fuel (usually coal) is fed through openings in the roof into the chamber where the temperature reaches approximately 1000°C to 1200°C.
- Cooling: As the fire moves to the next chamber, the previously fired chamber is cooled by incoming fresh air, which in turn becomes the preheated air for the firing zone.
A neat sketch would show a circular arrangement of chambers connected by a central flue system. The key components include the outer wall, inner wall, arched roof, firing holes (feed holes) on the top, and the central chimney. The fire travels in a circular path, completing one full rotation in the kiln over a period of 10 to 15 days depending on the number of chambers. This continuous operation allows for a constant output of high-quality bricks with minimal heat loss, making it the most economical method for mass production.
Explain different types of shakes in timber.
Answer
Shakes are longitudinal cracks or separations in the timber that extend between the annual rings. They are classified into the following types:
- Cup Shakes: These are curved splits that develop along the annual rings. They are caused by excessive bending of the growing tree due to strong winds or uneven growth.
- Heart Shakes: These occur in the center of the log, radiating from the pith towards the sapwood. They are typically caused by shrinkage of the heartwood as the tree ages or due to over-maturity.
- Star Shakes: These are a series of radial cracks that widen at the circumference and narrow towards the center. They often result from severe heat or rapid drying of the exterior of the log.
- Ring Shakes: Similar to cup shakes, these occur when the entire annual ring is separated. If a ring shake covers the complete circle, it is termed a ring shake, which severely weakens the timber.
- Radial Shakes: These are cracks that extend from the bark towards the pith, often caused by rapid drying of the outer surface of the timber.
Write down defects due to seasoning.
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Explain any two laboratory tests for cement.
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How the tensile strength of cement is determined in laboratory?
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What is the purpose of a lintel?
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Explain the following items in case of staircases (i) Balustrade (ii) Handrail (iii) soffit and (iv) pitch.
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Explain briefly classification of fire resistant materials.
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What do you understand by scaffolding? What are the essential requirements? What are the component parts of scaffold?
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List out different principles in planning a building. Explain any four factors in detail.
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