Brian M c Farland B.Eng (Hons) C.Eng M.ICE M.IEI M.ICorr MCS

Transcription

1 Carbonation, Chlorides & Electrochemical Repair Brian M c Farland B.Eng (Hons) C.Eng M.ICE M.IEI M.ICorr MCS M c Farland Associates Limited 2 nd Transnational Workshop duratinet The Queen s University of Belfast 22 nd June 2009

2 Overview Carbonation, Chlorides & Electrochemical Repair Carbonation Chloride Attack Inspection & Testing Traditional Repair Electrochemical Repair Case Histories

3 The Problem Millions of pounds are spent every year dealing with the symptoms of corrosion Expense Disruption Danger

4 The Cause of the Problem Poor design Chloride attack Carbonation Freeze thaw ASR Low cover Sulphate attack Poor site practice Impact damage Erosion Chemical attack

5 Carbonation Loss of passivated layer Carb on Dioxide Rust Carbon Dioxide

6 Chloride attack Passive layer destroyed, form ation of an anode and subsequent electrochemical pit corrosion C h lo rid e io n s penetrate concrete Chloride contam inated concrete

7 Chloride induced corrosion pits

8 Inspection & Testing

9 Chloride threshold values Chloride content Risk of (% cement) corrosion < Negligible Possible Probable > 2.0 Certain Ref: Browne (1982)

10 Half cell potential threshold values CSE Corrosion Condition >-200 mv Low 10% risk of corrosion to 350 mv Intermediate corrosion risk 1 < -350 mv High - <90% risk of corrosion 2 < -500 mv Severe corrosion 3 A B C D E

11 Traditional repair methods

12 BUT traditional patch repair alone does not..... Stop ongoing corrosion Prevent further spalling Break the repair cycle

13 Chasing the corrosion

14 BRE Digest 444 The problem the newly established cathodic area within the repair will drive the new anode site in the contaminated region How does this mechanism work?.

15 Chloride contaminated concrete prior to patch repair Chloride Chloride Chloride 0.8% 4.0% 0.8% Steel Concrete

16 Chloride contaminated concrete prior to patch repair Chloride Chloride Chloride 0.8% 4.0% 0.8% cathode anode cathode

17 Patch repair incipient i i anode effect Chloride Repair Chloride 0.8% 0.8% anode cathode anode

18 Downsides of Traditional Repair Break out all contaminated concrete Expensive Noisy Dusty Disruptive

19 Electrochemical Repair Electrochemical Repair Fighting Fire with Fire Cathodic Protection Realkalisation Chloride Extraction Sacrificial Anodes Next Generation Hybrid Systems

20 Cathodic Protection

21 Realkalisation Anode Electrolyte +ve -ve K 2CO3.KHCO 3 OH - Na+ Concrete Na+ K + Reinforcement

22 Chloride Extraction Current paths Anode Electrolyte +ve -ve Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Concrete Cl - OH - Cl - Reinforcement

23 Hydroxide Precipitation Proc. 7th Int. Conf. Concrete in Hot and Aggressive Environments, Vol. 2, p.477, 2003

24 Sacrificial Systems XP for patch repairs CC for blanket protection LJ for jetty piles

25 All the Galvashield systems work on the same principle

26 Oil Rig Example Photo Courtesy of Wilson Walton

27 Hybrid Systems Chloride extraction type process Cathodic prevention type process (low maintenance) Single electrode system

28 Hybrid Application Install discrete alloy electrodes Apply specialised electrochemical treatment for 1 week Connect activated sacrificial anode to steel

29 Hybrid Application Duoguard Anodes In Drilled Holes Temporary DC Power Supply (present for ~ 1 week)

30 Monitoring options Measure. Current Temperature Steel potential Residual life Manual monitoring box Automated monitoring box

31 Current output can be easily monitored sity (ma/m2) Current Den Eaton Park Pavillions, Norwich: CC anodes installed April 2001:Current Density results 6 30 July 01 Current Density (mam2) Temperature (degc) 25 5 June 02 June ure (degc) Temperat 1 0 Feb 03 0 Dec Time (days)

32 Residual life can be calculated Predicted anode life (Galvashied CC65) output / Am mps Current Life / Years

33 Comber Bridge

34 Comber Bridge

35 Comber Bridge

36 Comber Bridge

37 Carrick Leisure Centre

38 Carrick Leisure Centre

39 Lakeland Forum

40 Lakeland Forum

41 Eglinton Church

42 Eglinton Church

43 Red Arch Bridge

44 Red Arch Bridge

45 Red Arch Bridge

46 Ballylumford Jetty

47 Ballylumford Jetty

48 Beatties Bridge

49 Beatties Bridge

50 Conclusions Carbonation & Chloride Attack are the main problems encountered Traditional Repair alone rarely deals with the source of the problem Electrochemical Repair treats Fire with Fire and deals with the source of the problem reinforcement corrosion Realkalisation & Chloride Extraction are time consuming and costly Cathodic Protection requires a power source and monitoring and is prone to breaking down, vandalism and failure of the anodes Sacrificial Anodes are passive H b id S l ti i i th b fit f CP CE d SA ith t th Hybrid Solutions maximise the benefits of CP, CE and SAs without the downsides