Microbial biofilm development on and degradation of concrete surfaces
Abstract
Microbially induced corrosion (MIC) may result in severe concrete deterioration and incur great financial cost for infrastructure maintenance especially in extreme environments. Biofilm consisting of sulfur-oxidizing bacteria (SOB) on wet concrete surfaces may produce biogenic sulfuric acid under certain conditions which leads to structural degradation. Determination of the specific deterioration process is limited due to the failure of current research methods to simulate microbial activity and lack of appropriate test methods to characterize bacterial interaction with concrete surfaces. This study explored the corrosion mechanism at both meso- and micro-scale. Two biological simulation chambers were built to assess the influence of mixture proportions of concrete on the deterioration rate during MIC, using advanced sensors and controllers to automatically maintain the optical growth conditions for sulfur-oxidizing bacteria. Twelve mixture designs varying in water to cementitious materials ratios (w/c), supplementary cementitious materials (SCM), cement type, aggregate type, and air content were used in the test. Sample appearance, surface pH, mass, dynamic elastic modulus, and surface profile were monitored periodically. Results showed up to 3.2% of weight loss and an acceleration factor greater than 8 which confirmed the success of the chamber system development. Concrete mixtures with 0.30 w/c, fly ash replacement and Type V cement showed greater corrosion resistance than the other specimens. Noninvasive, self-referencing microsensors were used to characterize real time biofilm activity. The impact of different w/c, SCMs, cement types and the addition of anti-microbial chemicals on corrosion resistance were assessed. Specimens with w/c of 0.30, 0.42 and 0.60 had similar performance against deterioration. Increase in aluminum content could improve the corrosion resistance as calcium aluminate cement samples had the lowest corrosion rates. The effectiveness of the silicone quaternary ammonium salts against MIC was confirmed. An increase in admixture dosage and extending mixing time from 1.5 min to 7 min resulted in less corrosion rate. The bacterial function and interspecies activity during the corrosion process were also assessed. Results suggest that T. intermedius was similar to other Thiobacillus species; while T. novellus served as an intermediate.
Degree
Ph.D.
Advisors
Weiss, Purdue University.
Subject Area
Civil engineering|Environmental engineering
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