As per the IS 2185 (Part 1) : 2005, what is the minimum average compressive strength for open and closed cavity load-bearing masonry units?
🔬 Understanding the IS Code and Masonry Units
This question tests knowledge of a specific Indian Standard code that governs the quality of concrete masonry units (commonly known as concrete blocks or hollow blocks).
IS 2185 (Part 1) : 2005: This is the Bureau of Indian Standards (BIS) specification for Concrete Masonry Units, Part 1: Hollow and Solid Concrete Blocks.
Load-Bearing Units: These are blocks that are strong enough to carry the weight of the structure above them (like floors and roofs). Their compressive strength is a critical safety parameter.
Open and Closed Cavity: This refers to the design of hollow blocks. They have one or more large voids or cavities to reduce weight and improve thermal insulation.
⚖️ Detailed Analysis of the Compressive Strength Requirement
The IS code specifies different minimum strength requirements based on whether a block is intended to be load-bearing or non-load-bearing. For blocks that must support the structure, a minimum average strength is mandated to ensure safety.
(b) 3.5 N/mm²
Why it's correct: According to Table 2 of IS 2185 (Part 1), the minimum average compressive strength for hollow (open and closed cavity) concrete blocks designated as load-bearing is 3.5 N/mm². The standard also specifies that no individual block in the sample should have a strength less than 2.8 N/mm². This ensures a consistent and reliable quality for structural applications.
Analysis of Other Options
- (a) 1.5 N/mm²: This strength value is too low for load-bearing units. It is closer to the requirements for some types of non-load-bearing partition blocks.
- (c) 0.5 N/mm²: This is an extremely low value, typical of lightweight insulation blocks, not structural units.
- (d) 2.5 N/mm²: While some grades of solid blocks might be in this range, the specific minimum average for hollow load-bearing blocks is set at 3.5 N/mm².
💡 Study Tips for IS Codes
- Memorize Key Minimums: For exams, it's crucial to memorize the minimum specified values for common materials. For hollow load-bearing blocks, 3.5 N/mm² is the key number.
- Load-Bearing vs. Non-Load-Bearing: Always pay attention to this distinction. Structural (load-bearing) components will always have higher strength requirements than non-structural (non-load-bearing) components.
- Associate the Code with the Material: Link IS 2185 specifically with concrete blocks (both hollow and solid) to avoid confusing it with standards for clay bricks or other materials.