Selection of building stones – minimum specific gravity requirement For a good building stone, the specific gravity should generally be greater than which value?

Introduction:
Specific gravity is a practical indicator of a stone’s density and often correlates with strength and durability. This question checks the commonly cited threshold used in many construction texts for evaluating whether a stone is suitable for high-quality building work.

Given Data / Assumptions:

• We consider natural stones commonly used in masonry and structural applications.
• Higher specific gravity often implies greater density and potential strength.
• We choose the accepted benchmark value from standard references.

Concept / Approach:

Many civil engineering handbooks use 2.7 as a benchmark for the specific gravity of good building stones (e.g., granite, basalt). Stones significantly below this may be weaker or more porous, which can affect durability, abrasion resistance, and water absorption traits important for weathering and load-bearing use.

Step-by-Step Solution:

Verification / Alternative check:

Engineering property tables for building stones frequently list SG around or above 2.7 for preferred structural stones, supporting the threshold.

Why Other Options Are Wrong:

1.5 / 1.7: Far too low; would indicate very light, usually unsuitable stones.

2.2: Still low for many structural applications compared with high-quality dense stones.

Common Pitfalls:

Assuming any stone with SG above 2.2 is adequate; ignoring that other properties (water absorption, compressive strength) must also be checked in addition to SG.

Final Answer:

2.7