The provision of polyethylene encasement avoids the direct contact of ductile iron pipes with surrounding aggressive environment. However, polyethylene encasement is not intended as a water-tight system. Initially moisture between ductile iron pipes and polyethylene encasement contains some oxygen which shall be ultimately depleted and this would put a stop to the oxidation reaction. This process leads to a stable and stagnant environment near the pipe and it provides a protective environment.
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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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