Accelerated biodegradation of cured cement paste by Thiobacillus species under simulation condition

• The growth of Thiobacillus thioparus PTCC 1668 and Acidithiobacillus thiooxidans PTCC 1717 proceeded well on the surface of cured cement paste.
• Cement biodegradation occurred due to sulfuric acid formation and consumption of its components by bacteria.
• A semi-continuous A. thiooxidans culture induced the accelerated biodegradation of the cured cement paste.
• Bacteria take over the process of severe degradation of cement under simulated conditions within 90 days.

Biodegradation is one of the most important types of cement deterioration. Complex microbial populations take part in the biodegradation process of cement-based materials. Studies in this field show that the sulfur-oxidizing bacteria, including Acidithiobacillus thiooxidans, due to sulfuric acid formation, play a key role in this process. In this study, with the accelerated leaching process of calcium hydroxide of cement paste, cured under running tap water and exposed to sterile biogenic sulfuric acid for 6 days, the surface pH of the cement was reduced to a more favorable level for bacterial growth. In this case, the growth of Thiobacillus proceeded in the presence of cured cement paste specimens. After 90 days of exposure to a semi-continuous culture of A. thiooxidans with its pH less than 2 and continuous removal of damaged layers the compressive strength, length and mass of the samples dropped by 96%, 11% and 43%, in the order given. The mechanism of degradation and the structure of degraded specimens were analyzed by test laboratory techniques such as, XRD, SEM and EDAX analyses.