Quality testing of building stone: above what percentage of water absorption (by weight) should a stone be rejected for general construction use? (Choose the threshold beyond which durability and strength are considered inadequate.)

Difficulty: Easy

Correct Answer: More than 5%

Explanation:


Introduction / Context:
Water absorption is a key durability indicator for building stones. Excessive absorption correlates with higher porosity, reduced strength, frost susceptibility, and accelerated weathering. The question seeks the commonly accepted rejection threshold for general works.


Given Data / Assumptions:

  • Lower water absorption indicates denser, more durable stone.
  • General building specifications prefer stones with limited porosity.
  • Thresholds may vary by application, but a conservative general limit is used for screening.


Concept / Approach:
Stones with absorption above about 5% by weight are typically considered poor for general construction due to increased susceptibility to dampness, salt crystallization, and frost damage. Premium stones often exhibit absorption well below this value, while more porous varieties may be restricted to non-critical uses after treatment.


Step-by-Step Solution:

1) Recognize that absorption ≈ porosity → durability inverse relation.2) Industry practice uses 5% as a common upper limit for general works.3) Stones exceeding this are prone to deterioration and staining.4) Therefore, reject stones with absorption more than 5%.


Verification / Alternative check:
Traditional specifications and handbooks cite ≤5% as a desirable maximum for general construction stones, with lower values for severe exposure conditions.


Why Other Options Are Wrong:

  • 10%, 15%, 20%, 25%: too permissive; such high absorption indicates poor durability and is generally unsuitable for exposed or structural use.


Common Pitfalls:
Applying a single threshold to all environments (marine/freeze-thaw may demand stricter limits); ignoring sealing/finishing requirements that can mitigate but not fully offset high porosity.


Final Answer:
More than 5%

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