Study and evaluation of active corrosion protection coatings for reinforcement steel

Transcription

1 Study and evaluation of active corrosion protection coatings for reinforcement steel Hilke Verbruggen a,b, Florian Hiemer c, Sylvia Keßler c, Christophe Gehlen c, Herman Terryn a, Iris De Graeve a a Research Group Electrochemical and Surface Engineering (SURF) Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium b SIM vzw, Technologiepark 935, B-9052 Zwijnaarde, Belgium c Centre for Building Materials, Technische Universität München, Baumbachstrasse 7, Munich, Germany

2 deredactie.be Adapted from DS-infografiek (deredactie.be) 2

3 Problem? Spalling! combating-corrosion.php 3

4 How? In a concrete environment (ph 13) steel is passivated. However, with the ingress of corrosive species corrosion can occur Chlorides attack the passivation layer CO 2 reacts with Ca(OH) 2 to form CaCO 3 (=carbonation) Pitting corrosion Drop of ph (ph < 10) Uniform corrosion 4

5 Strategies to avoid the problem? Application of a coating Application of additional concrete cover Corrosion inhibitors Cathodic protection Physical barrier Active protection 5

6 Physical barrier + Active protection = Active = Double corrosion protection coatings for reinforced concrete 6

7 Outline Previous work Evaluation of inhibitors in different concrete pore solutions Application/incorporation of the inhibitor On the rebar/into an epoxy coating Evaluation of the coatings in concrete First results 7

8 Previous work Evaluation of inhibitors in different concrete pore solutions H. Verbruggen, H. Terryn, I. De Graeve, Inhibitor evaluation in different simulated concrete pore solution for the protection of steel rebars, Construction and Building Materials 124 (2016)

9 Screening of inhibitors against pitting corrosion 0.3 V 0.6 V All tested inhibitors, except for BTA, show some inhibition by counteracting the effect of salt and shifting the breakdown potential to 0,6 V. 9

10 Screening of inhibitors against uniform corrosion In this case only sodium molybdate shows some corrosion inhibition 10

11 Microscopic evaluation confirms Na 2 MoO 4 can inhibit both pitting and uniform corrosion Pitting corrosion Uniform corrosion Without inhibitor With Na 2 MoO 4 H. Verbruggen, H. Terryn, I. De Graeve, Inhibitor evaluation in different simulated concrete pore solution for the protection of steel rebars, Construction and Building Materials 124 (2016)

12 Application/incorporation of the inhibitor On the rebar/into an epoxy coating 12

13 Mixing in molybdate BECOPOX coating (Allnex): a water-based epoxy coating We prepared 36 % solid content to have the right viscosity for spray coating (0,06 0,1 Pa.s) We mixed 1 wt% (on solid content) Na 2 MoO 4 with the hardener and water (before adding the epoxies) 13

14 Molybdate pretreatment Inspired by - Active corrosion protection of steel by Ce containing conversion films, R. Ramanauskas, EUROCORR 2016, Montpellier, France, 15 September Molybdate conversion coatings on zinc surfaces, A.A.O. Magalhães et al., Journal of Electroanalytical Chemistry 572 (2004) We prepared a bath of 0.3 M Na 2 MoO 4 acidified with H 3 PO 4 (ph 3) and left the steel in for 10 min. 14

15 Evaluation of the coatings in concrete First results In collaboration with Centre for Building Materials, Technische Universität München 15

16 Preparation of samples Bare steel (bs) Reference coating (refcoat) Inhibitor mixed in the coating (ic) Inhibitor pretreatment (ip) Inhibitor pretreatment with coating on top (ipc) Rebars were spraycoated at OCAS; two layers were applied thickness 40 µm (!)

17 Preparation of the samples Side view: cathode anode Top view: TiO 2 mesh (counterelectrode) MnO 2 reference electrode 17

18 Preparation of samples Top view: In the coated samples (i.e. refcoat, ic, and ipc) a defect was applied by screwing a drill by hand, in both the anode and cathode Defect size = 0.2 mm² 18

19 Preparation of samples anode cathode TiO 2 mesh (CE) MnO 2 reference electrode

20 Preparation of the samples

21 Preparation of samples A crack (0.3 mm at surface) was introduced above the anode to simulate the worst condition

22 Set-up In cracked region weekly addition of 100 ml 1.5 % NaCl solution In outer regions weekly addition of tap water

23 Measurements in concrete Top view: anode cathode The corrosion current is recorded every 3 hours 23

24 Measurements in concrete Side view: RE WE cathode CE anode MnO2 RE Every week the corrosion potential is measured 24

25 Measurements in concrete Side view: cathode RE WE CE + anode MnO2 RE Every week the IR drop is measured 25

26 Measurements in concrete Side view: CE LPR anode (Gamry) RE WE anode TiO2 mesh MnO2 RE Every week after depolarisation the polarization the OCP resistance of the anode of the is measured anode is measured 26

27 Measurements in concrete Side view: cathode CE LPR cathode (Gamry) RE WE TiO2 mesh MnO2 RE Every week after depolarisation the OCP of the cathode is measured the polarization resistance of the cathode is measured 27

28 First results (after 12 weeks) Macro corrosion current (ma) Bare steel (bs 1) Potential (mv MnO2 ) Macro corrosion current OCP anode Potential (mv MnO2 ) OCP cathode Corrosion potential Time since first addition of NaCl solution (d) 28

29 First results (after 12 weeks) Macro corrosion current (ma) Reference coating (E+J) Potential (mv MnO2 ) Macro corrosion current OCP anode OCP cathode Corrosion potential Time since first addition of NaCl solution (d)

30 First results (after 12 weeks) Inhibitor mixed in the coating (ic OP) Macro corrosion current (ma) Potential (mv MnO2 ) Macro corrosion current OCP anode Time since first additon of NaCl solution (d) OCP cathode Corrosion potential 30

31 First results (after 12 weeks) Macro corrosion current (ma) Inhibitor pretreatment (ip 5+11) Potential (mv MnO2 ) Macro corrosion current OCP anode Time since first addition of NaCl solution (d) OCP cathode Corrosion potential 31

32 First results (after 12 weeks) Inhibitor pretreatment + coating (ipc 5+10) Macro corrosion current (ma) Potential (mv MnO2 ) Macro corrosion current OCP anode Time since first addition of NaCl solution (d) OCP cathode Corrosion potential 32

33 Short overview (after 12 weeks) Sample Corrosion potential, E corr (mv) IR Drop (mv) Driving potential, ΔE (mv) Rp (kω) Bare steel Reference coating Inhibitor mixed in Inhibitor pretreatment Inhibitor pretreatment + coating

34 (Mid-term) conclusions & outlook Bare steel needs some time to form a passive layer The (damaged) epoxy coating seems to favour corrosion When the inhibitor is mixed into the coating it can prolongate the initiation phase The inhibitor pretreatment (+ coating) rebars are protected from the beginning promising! Does it also protect on the long term?! What happens inside the concrete? 34