GATE CE 2016 Set 1 — Question 28
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Environmental Engineering → Wastewater Quantity & Sewerage → Design of Sewers
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Question
Crown corrosion in a reinforced concrete sewer is caused by:
Correct answer
(A) H₂S
Solution
Crown corrosion in sewers occurs when hydrogen sulfide () gas, produced by anaerobic decomposition of organic matter in sewage, escapes into the sewer atmosphere. It condenses on the moist upper surface (crown) of the sewer pipe, where aerobic bacteria (Thiobacillus) oxidize it to sulfuric acid (). The acid then reacts with the calcium hydroxide in the concrete, leading to structural degradation.
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