Study and evaluation of active corrosion protection coatings for reinforcement steel Hilke Verbruggen (hverbrug@vub.ac.be) 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, 81245 Munich, Germany
deredactie.be Adapted from DS-infografiek (deredactie.be) 2
Problem? Spalling! https://civildigital.com/spalling-concrete- causes-prevention-repair/ http://www.consysinc.net/ 3 combating-corrosion.php
How? In a concrete environment (pH ≈ 13) steel is passivated. However, with the ingress of corrosive species corrosion can occur Chlorides CO 2 attack the passivation layer reacts with Ca(OH) 2 to form CaCO 3 (=carbonation) Pitting corrosion Drop of pH (pH < 10) Uniform corrosion 4
Strategies to avoid the problem? Application of a coating Corrosion inhibitors Application of additional concrete cover Cathodic protection Physical barrier Active protection 5
+ Physical barrier Active protection = Active corrosion protection = Double corrosion protection coatings for reinforced concrete 6
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
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) 887 — 896. 8
Screening of inhibitors against pitting corrosion 0.6 V 0.3 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
Screening of inhibitors against uniform corrosion In this case only sodium molybdate shows some corrosion inhibition 10
Microscopic evaluation confirms Na 2 MoO 4 can inhibit both pitting and uniform corrosion Uniform corrosion Pitting 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 , 11 Construction and Building Materials 124 (2016) 887 — 896.
Application/incorporation of the inhibitor On the rebar/into an epoxy coating 12
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
Molybdate pretreatment Inspired by - “ Active corrosion protection of steel by Ce containing conversion films ”, R. Ramanauskas , EUROCORR 2016, Montpellier, France, 15 September 2016. - “ Molybdate conversion coatings on zinc surfaces”, A.A.O. Magalhães et al., Journal of Electroanalytical Chemistry 572 (2004) 433-440. 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
Evaluation of the coatings in concrete First results In collaboration with Centre for Building Materials, Technische Universität München 15
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 (!)
Preparation of the samples Side view: cathode anode TiO 2 mesh MnO 2 reference electrode (counterelectrode) Top view: 17
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
Preparation of samples anode cathode TiO 2 mesh (CE) MnO 2 reference electrode
Preparation of the samples
Preparation of samples A crack (0.3 mm at surface) was introduced above the anode to simulate the worst condition
Set-up In cracked region weekly addition of 100 ml 1.5 % NaCl solution In outer regions weekly addition of tap water
Measurements in concrete Top view: anode cathode The corrosion current is recorded every 3 hours 23
Measurements in concrete RE Side view: WE CE anode cathode MnO2 RE Every week the corrosion potential is measured 24
Measurements in concrete RE Side view: WE + CE anode cathode MnO2 RE Every week the IR drop is measured 25
Measurements in concrete RE Side view: LPR anode CE WE (Gamry) anode MnO2 RE TiO2 mesh Every week – after depolarisation – the OCP of the anode is measured the polarization resistance of the anode is measured 26
Measurements in concrete RE Side view: LPR cathode CE WE (Gamry) cathode MnO2 RE TiO2 mesh Every week – after depolarisation – the OCP of the cathode is measured the polarization resistance of the cathode is measured 27
First results (after 12 weeks) Bare steel (bs 1) Macro corrosion Potential (mV MnO2 ) current (mA) 0.010 0 Macro corrosion current -200 OCP anode -310 Potential (mV MnO2 ) 0.005 -400 OCP cathode -600 0.002 Corrosion potential 0.000 -800 0 14 28 42 56 70 84 98 Time since first addition of NaCl solution (d) 28
First results (after 12 weeks) Reference coating (E+J) Macro corrosion Potential (mV MnO2 ) current (mA) 0.010 0 Macro corrosion current -200 OCP anode 0.006 0.005 -400 OCP cathode -579 -600 Corrosion potential 0.000 -800 0 14 28 42 56 70 84 98 Time since first addition of NaCl solution (d) 29
First results (after 12 weeks) Inhibitor mixed in the coating (ic OP) Macro corrosion Potential (mV MnO2 ) current (mA) 0.010 0 Macro corrosion current -200 OCP anode 0.005 -400 OCP cathode -531 -600 0.002 Corrosion potential 0.000 -800 0 14 28 42 56 70 84 98 Time since first additon of NaCl solution (d) 30
First results (after 12 weeks) Inhibitor pretreatment (ip 5+11) Macro corrosion Potential (mV MnO2 ) current (mA) 0.010 0 Macro corrosion current -200 OCP anode -398 0.005 -400 OCP cathode -600 Corrosion potential 0.000 0.000 -800 0 14 28 42 56 70 84 98 Time since first addition of NaCl solution (d) 31
First results (after 12 weeks) Inhibitor pretreatment + coating (ipc 5+10) Macro corrosion Potential (mV MnO2 ) current (mA) 0.010 0 Macro corrosion current -200 -262 OCP anode 0.005 -400 OCP cathode -600 Corrosion potential 0.000 0.000 -800 0 14 28 42 56 70 84 98 Time since first addition of NaCl solution (d) 32
Short overview (after 12 weeks) Corrosion Driving Sample potential, E corr IR Drop (mV) potential, Δ E Rp (k Ω ) (mV) (mV) Bare steel -310 0 51 20.17 Reference -579 12 218 4.37 coating Inhibitor -531 20 191 13.73 mixed in Inhibitor -398 0 -22 18.18 pretreatment Inhibitor pretreatment -262 0 8 18.25 + coating 33
(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
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