モルタルの微生物腐食について

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タイトル別名
  • Study on Biological Mortar Corrosion
  • モルタル ノ ビセイブツ フショク ニ ツイテ

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Concrete sewer pipes are microbiologically corroded due to a two step reaction, i.e., productions of hydrogen sulfide (H2S) and sulfuric acid (H2SO4) caused by sulfate reducing bacteria and sulfide oxidizing bacteria, respectively.<BR>To estimate the in-situ corrosion rate, ordinary Portland cement mortar specimens (4×4×16cm) were placed in the manhole of a corroded pipe. The maximum and average corrosion rates were determined to be 3 and 1 mm/month, respectively. Temperature ranged from 25 to 30°C.<BR>The ordinary Portland cement mortar specimens were placed in the vessel in the laboratory, too. The gaseous H2S concentration was kept at about 500 ppm and temperature changed from 10 to 25°C. Specimens in the vessel were put into sewage, A-T medium or distilled water. The corrosion rate of the specimen dipped in the sewage was larger than that of the ones in the A-T medium. The specimens did not corrode at all in distilled water.<BR>In addition, expansive cement mortar specimens and ordinary Portland cement mortar specimens were put into 5% Na2SO4 solutions, respectively. The former showed a greater deterioration rate than the latter.<BR>It can be said from these results, that nutrients and temperature greatly affected the rate of corrosion. Corroded materials with a pH of from 0-2 mainly consisted of gypsum and ettringite was found at a much higher.pH. Since concrete sewer pipes are made with expansive cement, these are severely attacked by both sulfuric acid and sulfate.

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