PRETEND INTELLECTUAL INVESTIGATION ON REINFORCEMENT CORROSION IN BACTERIAL CONCRETE USING IMPRESSED CURRENT TECHNIQUE METHOD

  • Unique Paper ID: 167246
  • Volume: 11
  • Issue: 3
  • PageNo: 948-959
  • Abstract:
  • Reinforced concrete structures form a major part of the engineering infrastructure of all developed countries, and their integrity over long periods of service is of vital economic importance. But the major drawback is its low tensile strength which causes cracking in concrete. When micro cracks growth reaches the reinforcement, not only the concrete gets damaged, but also corrosion occurs in the reinforcement due to exposure to water and oxygen, and possibly CO2 and chlorides too. Micro-cracks are therefore the main cause for structural failure. For crack repair, a variety of techniques are available but traditional repair systems have a number of disadvantageous aspects such as different thermal expansion coefficient compared to concrete and also have impact on environment and health. Therefore, bio based calcite precipitation has been proposed as an alternative and sustainable environmental friendly crack repair technique. Bio-mineralization of calcium carbonate is one such strategy to remediate cracks in building materials. The consumption of oxygen during the metabolic biochemical reactions to form CaCO3 is expected to help in arresting corrosion of steel because the oxygen is responsible to initiate the process of corrosion thereby increasing the durability of steel reinforced concrete structures. In this thesis, an attempt has been made in the first phase to find the optimum concentration of bacterial cells to be incorporated in concrete. Based on the state-of-the-art information available in the literature three different bacterial samples are considered in concentrations of 104,105 and 106 cells/ml. The bacteria considered are Bacillus subtilis, Pseudomonas aerugonisa and Bacillus megaterium and the optimum concentration is found to be 105, 105 and 104cells/ml respectively based on compressive strength results. The increase in strength is found to be 42.8, 50.5 and 53.5% respectively for Bacillus subtilis, Pseudomonas aerugonisa and Bacillus megaterium respectively. Water absorption test is carried out on cubes cast with optimum concentration of bacterial cells. The percentage water absorbed was found to be lesser for specimens with bacteria. This confirms that the bacteria plug the pores in concrete. A maximum of 20.12% reduction in water absorption was obtained for Bacillus megaterium when compared with control mix. In the next phase of the study, corrosion is accelerated by impressed current technique in the reinforced concrete beams cast with optimum concentration of each bacterium and the conventional RC beams. In this study, the corrosion of tension reinforcement is only considered. Lead wires are connected at two points of each tension reinforcements to induce uniform corrosion in the rebars. 5% sodium chloride solution is used as electrolyte to simulate sea water environment. The rebars are initially weighed before they are embedded in concrete. The acceleration process is carried out for a period of 120 hours by galvanostatic method with steel rebars as anode, stainless steel plate as cathode and NaCl as electrolyte. The beams are then destroyed and the rebars are extracted, cleaned and then weighed. Current applied for inducing corrosion is not found to be fully efficient in causing loss of mass equal to that theoretically predicted by Faraday’s Law. Therefore, a plot of Iapp vs Icorr is obtained for each type of specimen to study the relationship between applied and induced current. The degree of induced corrosion is expressed in terms of percentage weight loss. The mass loss percentages were higher for control specimens when compared with bacterial specimens. The average mass loss was found to be 5.17% for control beams, 2.83% for Bacillus subtilis, 3.02% for Pseudomonas aeruginosa, and 2.62% for Bacillus megaterium specimens. Bacillus megaterium specimens exhibited maximum difference of loss in weight when compared to control beams. Thus the corrosion resistance property of bacterial concrete was found to be higher than the control mix without bacteria..

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