208th ECS Meeting, Abstract #358, copyright ECS
Fig.2 El.resisitivity vs time
Fig 2: a) Rp vs time and b) Ecorr vs time
-Fig. 3 Cl concentrations per prism sections vs time
Fig. 4 Polarization measurements steel
cement paste
Conventional and pulse cathodic protection
of reinforced concrete: electrochemical
approach and microstructural investigations.
1 1 1 2 1
D.A.Koleva , J.Hu , K.v.Breugel , N.Boshkov , H.de Wit
1
TUD, Stevinweg 1, 2628 CN Delft, The Netherlands
2
BAS - IPC, G.Binchev,bl.11 ,Sofia, Bulgaria An improved cathodic protection (CP), based on pulse regime, was investigated on reinforced concrete, compared to conventional CP. The influence of steady and pulse DC on the concrete microstructure and ion migration (using CP
2
current of 5 to 10 mA/m , pulse achieved with 12 to 50% duty cycle at certain frequency), was preliminary investigated on concrete specimens (100x100x300 mm)
-Fig. 1, differing in set-up in terms of Cl concentration. Electrical resisitivity monitoring (Fig.2) and ion concentrations measurements were performed, aiming at investigation of the concrete response to CP current. Pulse
-DC is more efficient in enhancing the Cl migration towards the anode and reducing the aggressive ion concentration around the cathode Fig.3. Polarization measurements are in favor of the pulse regime in terms of achieving the initial terminal voltage with the same time constant as the steady DC Fig.4. Moreover, pulse DC is less detrimental to the bulk material microstructure in terms of porosity, interconnectivity and micro-cracking - Figs.5 (a-c). Reinforced concrete cylinders (120x250 mm) Fig.6, were cast in 2 groups, differing in composition Group A using tap water and group B using 5 % NaCl solution as mixing water. Groups A and B were divided into groups, differing in technical conditions under CP, under pulse CP, in rest conditions (freely corroding) and reference (non-corroding). All cells had embedded: two construction steel
bars, d=12 mm, Mn/MnO reference cells and MMO Ti2
mesh on the outer surface (serving as anode) Fig.6. All specimens were produced using OPC CEM I 32.5 with cement-to-sand ratio 1:3, water-to-cement ratio 0.6, conditioned in fog room for 14 days (98% RH, 20C) and placed (except the reference) in salt spray chamber (5%
2
NaCl) afterwards. Pulse and conventional CP (2mA/m ) were applied on some specimens at 30 days of age, aiming monitoring of the efficiency of both techniques as prevention methods. The rest were left to freely corrode for approximately 90 days. Potential mapping and electrochemical measurements i.e. EIS and LPR were performed for all groups of specimens aiming determination of polarization resistance and corrosion current (EIS in frequency range of 50kHz to10mHz and
LPR at 20 mV close to E at scan rate 0.2 mV/s, the corr
measurements for the CP-ed specimens being done after 24 h depolarization). At the age of 90 days of cement hydration, CP (pulse and conventional) was applied to part of the corroding specimens. All groups (CP and pulse CP) achieved the required polarization with various time constants, but after a certain period of about 1 to 12 days, all potential readings were in the range of -900 to -1100 mV vs SCE.
Micro-structure investigation of product layers on the steel surface of freely corroding and protected specimens was performed using electron microscopy and X-ray analysis. The efficiency of CP was visualized by the presence of relatively flat and compact layer of magnetite in the protected specimens (Fig.7a), compared to flower-like iron oxides and oxy-chlorides in the corroding specimens (Fig.7b).
Polarization measurements for samples D2p DC (pulse) and D3 DC(steady), dry and wet
conditions (1750) (1500) (1250) (1000) (750) (500) (250) 0 19:12 4:48 14:24 0:00 9:36 19:12 4:48 time[h] Vo lt a g e d ro p [m V ] D2pDC D3 DC D2-pDCwet D3-Dcwet D3 DC D2 pDC D3 DC Wet D2p DC Wet
Total Re sisitivity (kOhm cm) vs Time (days) samples DN1 re st, DN2-pulse DC, DN3-DC 0 5 10 15 20 25 30 35 0 20 40 60 80100120140160180200 Time (days ) Re si si ti v it y (k O h m c m ) changed pulse pattern climate room
el.field applied on samples DN2 and DN3
DN1 DN3 DN2 Fig.1 Experimental set-up
corrosion products steel 0 50 100 150 200 250 300 109 days 86 days 64 days DC current pulse DC current
m m ol C l-/c e m e nt w e ight prisms sections A2 B2 A2 B2
Fig. 5a Rest conditions
Fig 5b DC regime
Fig.5c Pulse DC regime
Fig.6 Experimental set
Reinforced concrete cylinder
Fig.7a Protected specimen Fig.7b Corroding specimen
The combination of electrical, electrochemical and microstructural techniques provides a detailed understanding of corrosion process and the efficiency of CP. CP is so far one of the most viable techniques for inhibiting chloride induced corrosion in reinforced concrete. However, the side effects as loss of bond strength, overprotection, micro structural alterations and micro-cracks, can be minimized by an improved technique. In this sense, pulse CP is able to minimize the negative side effects and efficiently protect the steel reinforcement.
bulk ITZ bulk ITZ bulk ITZ + +
