COST ACTION 534. WG 2: New system. Internal reference electrode to detect steel corrosion. CMIC Giulio Natta - Politecnico di Milano

Transcription

1 COST ACTION 534 New materials, systems, methods and concepts for durable prestressed concrete structures WG 2: New system Internal reference electrode to detect steel corrosion L. Lazzari,, M. Ormellese, P. Pedeferri CMIC Giulio Natta - Politecnico di Milano

2 Aim of the project Study of a new electrochemical technique to monitor the occurrence of localised corrosion Post-tensioned tendons and pre-stressed strands Pre-stressed concrete cylinder pipes, PCCP Continuous monitoring of reinforced structures 1995: Wietek proposed the use of a Linear Continuous Reference Electrode, LCRE US 5,403,550 patent no documented applications no indication about the mechanism 2

3 Potential mapping 3

4 Potential mapping 4

5 Phases of the research 1995: Wietek proposed the use of a Linear Continuous Reference Electrode, LCRE Phase A: A Lab tests on LCRE (2004) detection of localised corrosion mechanism of detection limitation Phase B: B development of Multi Reference Electrode, MuRE ( ) lab tests: detection of pit initiation FEM simulation to study possible application to prestressedcylinder-concrete-pipe (PCCP), viaduct, for pit initiation monitoring and continuous potential mapping Italian patent, MI2004A (2004) Phase C: MuRE field applications (2006- ) 5

6 Phases of the research 1995: Wietek proposed the use of a Linear Continuous Reference Electrode, LCRE Phase A: A Lab tests on LCRE (2004) detection of localised corrosion mechanism of detection limitation Phase B: B development of Multi Reference Electrode, MuRE ( ) lab tests: detection of pit initiation Italian patent, MI2004A (2004) FEM simulation to study possible application to prestressedcylinder-concrete-pipe (PCCP), viaduct, for pit initiation monitoring and continuous potential mapping Phase C: MuRE field applications (2006- ) 6

7 Phase A: study of LCRE system Aim of the experiments Detection of corrosion Interpretation of potential readings Limitation Tests Solution, mortar and concrete 7

8 Phase A: LCRE system! " #$ 8

9 Phase A: study of LCRE system Main conclusion: LCRE detects corrosion for small geometry LCRE behaves as an interfered electrode The measured potential can be interpreted as the average potential weighted on the equipotential surface area Higher is the extension of the cathodic area, lower is the sensitivity of the LCRE 9

10 Phase B: MuRE system LCRE Passive area Anodic area Passive area 10

11 Phase B: MuRE system MuRE: Multi Reference Electrode system Passive area Anodic area Passive area 11

12 Phase B: MuRE system Aim of the experiments develop a Multi Reference Electrode system (MuRE) verify the ability to detect localised corrosion determine proper L/D ratio possible applications (FEM simulation) Tests laboratory tests: grout stability in alkaline environment: copper stainless steel nickel % && 12 ( && '

13 Phase B: MuRE system ) *' ($!"!"!" #$ 13

14 Phase B: MuRE system Main conclusions: MuRE behaves as an interfered electrode immersed in an electrical field Measured potential is the weighted average of potential of anodic and cathodic area MuRE is able to promptly detect and localise the corrosion attack the maximum allowable length/cover ratio to detect the localised corrosion is 50 14

15 Phase C: MuRE field applications Pre-stressed concrete cylinder pipe, PCCP Continuos monitoring in viaduct Post-tensioned tendon Pre-stressed concrete beam 15

16 Phase C: MuRE field applications Venice: barrier MOSE project, Chioggia inlet Two pre-stressed concrete beams Installation: May 2007 (by CESCOR srl) In cooperation with TECHNITAL and CLODIA Turin: tunnel, high speed train (TAV) Two pre-stressed concrete beams Installation: April 2007 (by CESCOR srl) In cooperation with ITALFERR and ASTALDI Turin: highway Two post-tensioned concrete spam Installation: January

17 Phase C: MuRE field applications Venice: barrier MOSE project, Chioggia inlet two pre-stressed concrete beams: 20 m long installation: May 2007 Nickel MuRE 12 reference electrodes reference electrode length: 1.5 m total diameter: 10 mm Measurements electrical isolation before and after casting potential monitoring 17

18 Phase C: MuRE field applications +,&! # '- ( #,#) +,&! # 10 mm 18

19 Phase C: MuRE field applications.#### ( +,&! # 19

20 Phase C: MuRE field applications /%* ( 0### +,&! # 20

21 Phase C: MuRE field applications /% ( 10 mm +,&! # 21

22 Phase C: MuRE field applications 22

23 Phase C: MuRE field applications Electrical isolation measurements before casting: R > 40 MΩ No accidental electrical contact MuRE-steel after casting: R = 1 4 MΩ Good contact MuRE-concrete 23

24 Phase C: MuRE field applications Potential measurements Venice beams Turin beams 1#' $ after 5 months after casting 1#' $ after 6 months after casting! 2) *0) $! 2) *0) $ / " # $ %& ' " # $ %& 24

25 Conclusion A new monitoring electrochemical system has been design, called MuRE Lab tests and FEM simulation confirm that the MuRE system is able to detect and localise the onset of chloride-induced corrosion First data by field applications confirm the MuRE is working as expected 25

26 26

27 27

28 Potential mapping 28

29 Phase A: LCRE system Solution and concrete cell tests - + Galvanostat I Anode Simulating the pit LCRE Grout 6 cm rebar 60 cm Internal fixed RE 29

30 Phase A: LCRE system (**,. WG 2: New System Ormellese 30

31 Phase A: LCRE system "#" %!//!'!// '(# "! 3 # 0 # %! 31

32 Phase A: LCRE system * #" & 44 " % %! # $' #$()*+,',, -,' -,)*+,',, 32

33 Phase A: LCRE system * The value measured is the weighted average of the potential profile = = = = $%$& &$'()*+,.+,+,*).+/,,, 0.**,.//, 33

34 Phase B: MuRE system Samples 2.5 m long 50 mm diameter carbon steel rebar Φ = 10 mm D = 20 mm grout Water/Cement = 0.3 super-plasticizer 4% by cem wt RE materials copper (100%) stainless steel (UNS S31600) nickel (Ni 95% - Ti 4% - Si 1%) oxidised stainless steel L/D ratio LCRE for comparison 34

35 Phase B: MuRE system ", ) * "!"!"!" #$ SS-MuRE 35

36 Application of MuRE to PCCP PCCP in contact with Cl- solutions Risk of hydrogen embrittlement Some failures occurred on sections of PCCP CP was applied to avoid pit initiation WG 2: New System Ormellese 36

37 Application of MuRE to PCCP GMMR: Great Man Made River (Libya) 4 m in diameter PCCP a reliable potential monitoring should require a huge number of reference electrodes located around the pipe and all along the pipe To have an acceptable potential mapping of the steel wire surface, approximately a grid of 0.5 m mesh should be used (i.e., about 48 RE per meter are required) 37

38 Application of MuRE to PCCP A simulation by Finite Element Method, FEM, was performed with the following input and conditions: pit surface area = m2 of in any point of the wire surface concrete cover = 0.03 m pipe external diameter = 4 m soil conductivity = 0.1 (Ωm)-1 concrete cover conductivity = 0.02 (Ωm)-1 = ( ) ( ) 1 1 ( ) 1 ( ) = 1 38

39 Application of MuRE to PCCP pit 39

40 Application of MuRE to PCCP pit 40

41 Application of MuRE to PCCP 41

42 Application of MuRE to PCCP - $& *0) $ 42

43 Application of MuRE to PCCP Effective length of the MuRE was calculated to detect a difference in potential of 100, 200 and 300 mv between passive and active steel condition = = Length resulted: 5 m, 3.5 m to 1.5 m, respectively 43

44 Application of MuRE to PCCP The MuRE system can be used for PCCP to monitor pitting initiation and to prevent HE of pre-stressed wire By means of computer modeling simulation the active length of the reference electrode was calculated as a function of maximum potential variation The linear reference electrode can also be used to check CP level, taking into account that the shorter the active electrode length the little is the range of potential variation 44

45 MuRE for continuous mapping 45

46 MuRE for continuous mapping MuRE (. + /

47 MuRE for continuous mapping MuRE 1 MuRE V V MuRE V corroded area!!!! MuRE 4 MuRE 5 MuRE 6 MuRE V V V V MuRE is able to detect and localized the corroded area by a continuous mapping 47