Jawaharlal Nehru Technological University Hyderabad B.Tech II BUILDING MATERIALS CONSTRUCTION AND PLANNING Previous Question Paper (November/December - 2020 - R13)

A good building stone must possess specific physical, chemical, and mechanical characteristics to ensure the durability and stability of a structure. The primary requirements are:

• Strength: The stone must have sufficient compressive strength to withstand the loads imposed by the structure.
• Durability: It should be able to resist the disintegrating effects of weather, such as rain, frost, and temperature variations.
• Hardness: The stone must be hard enough to resist abrasive forces caused by foot traffic or friction, particularly for flooring and paving.
• Toughness: It should be able to withstand impact or vibration without cracking or breaking.
• Low Porosity and Absorption: Stones with low water absorption are less prone to weathering and chemical decay.
• Appearance: For facing work, the stone should be uniform in color and capable of taking a good polish.
• Workability: It should be easy to quarry, dress, and carve into desired shapes.
• Seasoning: The stone should be free from quarry sap to ensure it hardens properly after extraction.

The selection of stone for construction depends on several critical properties that dictate its performance in different environmental conditions:

1. Specific Gravity: This is a measure of the density of the stone. A higher specific gravity (typically above 2.4) indicates a denser, stronger, and less porous stone, which is generally more suitable for heavy engineering works like dams or bridge piers.
2. Compressive Strength: This property determines the load-bearing capacity. For most structural applications, the stone must have a high compressive strength to prevent crushing under the weight of the building.
3. Resistance to Weathering: The stone must be resistant to chemical and physical weathering agents such as acid rain, oxidation, and freeze-thaw cycles. This is crucial for external cladding and exposed masonry.
4. Water Absorption: A stone with high water absorption is undesirable as it allows moisture to penetrate, leading to cracks during freezing and encouraging the growth of moss or chemical degradation. Stones with absorption less than 5% are generally preferred.
5. Texture and Structure: The internal arrangement of grains affects both the strength and the ease of working. A fine-grained, uniform texture is usually stronger and more durable than a coarse-grained or heterogeneous structure.