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Predicting Time for Corrosion Initiation in Reinforced concrete
 

Predicting Time for Corrosion Initiation in Reinforced concrete

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  • A discount rate must represent the cost of capital and a reasonable opportunity cost.
  • When at cover depth, chloride content reaches the critical chloride content, the passive layer breaks and corrosion starts.
  • Aggregate : Impermeable
  • In deterministic methods, all the input values are given a discrete fixed value and any type ofuncertainty is ignored in determining the Life Cycle Cost.
  • the probabilistic distribution assigned to each variable provides aclearer and more descriptive picture of associated outcomes.Here, Monte Carlo simulation is used

Predicting Time for Corrosion Initiation in Reinforced concrete Predicting Time for Corrosion Initiation in Reinforced concrete Presentation Transcript

  • Service Life Prediction of Reinforced Concrete exposed to Chloride Environment based on Corrosion Initiation Ankur Bansal 09010408Footer Text 11/17/2012 1
  • Points to be Discussed• Cause of Reinforcement Corrosion• Phases involved in corrosion of reinforcement.• Factors affecting the diffusion of chloride into concrete.• Models to determine the time for corrosion initiation• Experimental Work done to determine the critical chloride content.• Conclusion and Future Work Footer Text 11/17/2012 2
  • Cause of Reinforcement Corrosion• The high alkalinity of the concrete pore solution provides a protection of steel bars in concrete against corrosion• Corrosive ions and molecules such as chloride ions and carbon dioxide reach the surface steel and break the passivation film and the corrosion starts.Footer Text 11/17/2012 3
  • Phases involved in Reinforcement Corrosion• Corrosion Initiation• Corrosion PropagationFooter Text 11/17/2012 4
  • Parameters involved in chloride diffusionFooter Text 11/17/2012 5
  • Factors affecting Chloride Transport• Concrete Mix  Type of cement used.  Water binder ratio.  Aggregate Size.• Curing Conditions• Exposure ConditionsFooter Text 11/17/2012 6
  • Models to determinecorrosion initiation periodDeterministic• An Exact Time period is determinedProbabilistic• A range of Values is determined with a specific probability distribution.Footer Text 11/17/2012 7
  • Deterministic ApproachFooter Text 11/17/2012 8
  • Probabilistic Approach• Experiments are performed many times and a distribution of the values are found.• Random numbers are generated according the distribution achieved(2 lakhs in our case).• These values are put into the diffusion equation.Footer Text 11/17/2012 9
  • Probabilistic Approach• Then at a given time period, no. of times the chloride content at reinforcement surface exceeds the critical chloride content is given by n and total number of experiments are N.• Thus, Probability of failure is given by Pf = n/N Footer Text 11/17/2012 10
  • Simulation ResultsDistributions of different parameters for a specificproject were found by (Ha-Won, et al., 2009)Variables Units Mean Standard Distribution Deviation FunctionD 3.77 0.91 NormalCs % of binder 2.83 0.72 GEV (General Extreme Value)Ccrit % of binder 0.69 0.30 Gumbel Footer Text 11/17/2012 11
  • Generated Random Numbers 4 x 10 2.5 2 No. of samples 1.5 1 0.5 0 1 2 3 4 5 6 7 8 9 10 Surface Chloride Content General Extreme value distribution for values of Surface Chloride Content.Footer Text 11/17/2012 12
  • Generated Random Numbers 4 x 10 2.5 2 Number of Samples 1.5 1 0.5 0 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 Critical Chloride Content Gumbel Distribution for values of critical chloride content.Footer Text 11/17/2012 13
  • Generated Random Numbers 14000 12000 10000 Number of Samples 8000 6000 4000 2000 0 -1 0 1 2 3 4 5 6 7 8 Diffusion Coefficient -12 x 10 Generated values of Diffusion Coefficient with normal distribution.Footer Text 11/17/2012 14
  • Probability of corrosion initiation v/s time 0.09 0.08 0.07 0.06 X: 130 Probability of failure Y: 0.05114 0.05 0.04 0.03 0.02 0.01 0 20 40 60 80 100 120 140 160 Time Period After 130 years, 5 % of the samples will fail.Footer Text 11/17/2012 15
  • Experimental Work• Concrete mixes of different w/c ratio and different cement type are planned to be prepared.• 3 Cubes and 3 beams of different cover depths i.e. 25mm, 35mm and 44mm were casted.• 28 days Compressive Strength of the cubes was determined• Beams were Kept in a 9 % NaCl Solution with a potential difference of 12.0 Volts between reinforcement bar and surrounding solution. Footer Text 11/17/2012 16
  • Test Results• Compressive Strength For concrete Mix with w/c 0.5 using OPC Cement, compressive strength was found to be 26.07 MPa. For concrete Mix with w/c 0.55 using OPC Cement, compressive strength was found to be 23.6 MPa. Footer Text 11/17/2012 17
  • Test Results• Accelerated Corrosion Test(for OPC and w/c 0.5 ) 0.16 0.14 0.12 Current(A) 0.1 0.08 25mm 0.06 35mm 0.04 44mm 0.02 0 0 10 20 30 40 50 60 70 80 Exposure Time (hours) Plot of Current v/s Exposure Time Footer Text 11/17/2012 18
  • Footer Text Current(A) 0 0.1 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.001359333 0.001390667 0.001418667 0.001434333 0.001459333 0.001478167 0.001484333 0.001481167 0.001478167 0.001468667 0.001456333 0.00145 0.0014375 0.001425 0.0014125 Time (hours) 0.0014 0.0013875 0.001375 0.0013625 0.001359333 0.001353167 0.001346833 0.001343667 Test Results 0.0013375 0.001328167 0.001303167 • Accelerated Corrosion Test (w/c = 0.55, OPC) 25 mm 35 mm11/17/201219
  • Conclusion and Future WorkFooter Text 11/17/2012 20