Study of Reinforced Concrete Corrosion Using Impedance Measurements

Transcription

1 Study of Reinforced Concrete Corrosion Using Impedance Measurements

2 Objective To develop a new non-destructive method that uses a multielectrode electrical resistivity array to measure the complex impedance along the surface of a concrete structure in order to determine the position of the reinforcing bars and their corrosion state

3 Challenges 1) It should be able to locate the reinforcing bar, and be able to localize the measurement to identify the location of a bar undergoing corrosion. 2) It must make the measurement from the surface of concrete 3) It must measure the electrical resistivity of the concrete itself. 4) It must measure the properties of the interface. 5) It must be simple to use and require a minimum of data processing.

4 The Method A Rc1 M Rc2 N Rc3 B Rc4 Rc5 Z Z Rcm

5 The Proof of Concept

6 Cast a large concrete block with different bars

7 Gold bar

8 Casting

9 Block

10 Rebars were located and their surface identified Rebar No.1, As recieved No.2, Clean No.3, Painted No.4, Gold-coated e-03 1e-02 1e-01 1e+00 1e+01 1e+02 1e+03 Frequency(Hz)

11 Test set-up

12 Results

13 Results (2) 30 Specimen A2 Pseudosection location ρ 2,1 20 Free corrosion 0.05 µa/cm µa/cm µa/cm 2 10 µa/cm e-03 1e-02 1e-01 1e+00 1e+01 1e+02 1e+03 1e+04 Frequency(Hz)

14 Results Free corrosion 0.05 µa/cm µa/cm µa/cm 2 10 µa/cm 2 0.1Hz Hz Real (Ω.m)

15 Looks good but life is never that easy... to become quantitative needs to solve the inverse problem

16 Model Input I Prospecting of V I D y a Concrete,ρ 1 y θ r 2r 0 x z Rebar, ρ 0 z x Interface, z interface Plane yz for x = 0 Plane xy for z = 0

17 Fundamental equations Poisson equation: 1 r r ( V(r) r ) V(r) r 2 θ V(r) z 2 = I 4π ρ 1 δ(r r s ) Solutions in the concrete (V1) and in the rebar (V0) are: V 0 (r,z) = I 2π 2 V 1 (r,z) = V p (r,z) + 0[ ] A m (u)i m (ur)cos(uz)du cos(m(θ θ 0 )) 0 m= I 2π 2 0[ B m (u)k m (ur)cos(uz)du] cos(m(θ θ 0 )) 0 m=

18 Coefficients [ ( 2 δ 0m )K m (ur s )I m ) ] u I m 1 ) m I m ) σ 0 r 0 σ 1 I m ) + Z interface σ 1 (ui m 1 ) m I m ) ( 2 δ 0m )K m (ur s ) ui m 1 ) m I m ) uk r m 1 ) mk m ) r r 0 B m (u) = 0 σ 0 uk m 1 ) mk m ) σ K m ) u I m 1 ) m I (ur ) m 0 1 r r 0 I m ) + Z interface σ 1 (ui m 1 ) m I (ur ) m 0 r 0 ( 2 δ A m (u) = 0m )K m (ur s )I m ) + B m (u)k m ) I m ) + Z interface σ 1 (ui m 1 ) m I m ) r 0 Yes, it does get more complicated than this because we need to solve for the half-space (please see paper for details)

19 Once model is done we can run simulations Hz Cd Re 10 Rp Hz Interface impedance simulated by the simple electrical circuit R = Ω.m 2 e Cd=0.15F/m 2 R =2.5 Ω.m 2 p R =25 Ω.m 2 p Real (Ω.m 2 )

20 Electrode distance na / the concrete cover D (na/d) 1. Geometry effect Electrode array: Wenner Concrete cover D / rebar radius r 0 D/r =3 0 D/r =2 0 D/r = r = m (1/2 in.) 0 ρ =100 Ω.m (concrete) 1 ρ =0.01 Ω.m (rebar)

21 2. Apparent resistivity response with corrosion rate Concrete, rebar, and geometric properties ρ concrete =50 Ω.m ρ rebar =10-6 Ω.m D= m (1 in.) r = (1/4 in.) Hz Hz 1 Hz 1 Hz Hz Hz Interface impedance simulated by the simple electrical circuit R = Ω.m 2 e Cd=0.15F/m 2 R =2.5 Ω.m 2 p R =25 Ω.m 2 p Real (Ω.m 2 ) 10 Rp=2.5 Ω.m 2 Rp=25 Ω.m Real (Ω.m)

22 3. Geometry effect on corrosion measurement 20 Concrete, rebar, and geometric properties ρ concrete =50 Ω.m ρ rebar =10-6 Ω.m 15 Interface impedance Rp=2.5 Ω.m 2, Cd=0.15F /m 2 10 r 0 = m(0.25 in.) D= m (1 in.) D=0.0381m (1.5 in.) 5 0 1e-04 1e-03 1e-02 1e-01 1e+00 1e+01 1e+02 1e+03 1e+04 Frequency (Hz)

23 Conclusions The Surface Measurement Method accurately detects the different corrosion states of embedded reinforcing bars in concrete structures. This method is applied on the structure surface, with no need to connect with the reinforcement. In addition, it localizes the measurement to a confined segment of the rebar beneath the electrode array.

24 Conclusions The measured resistivity spectra distinguish various corrosion rates and various corrosion extents. The decreased resistivity modulus and peak phase angle can be used to characterize how rapidly the reinforcing bar is corroding, and the peak phase angle shift to a smaller frequency indicates to what extent the reinforcing bar has corroded.

25 Conclusions The analytical solution is obtained to the surface-based measurement of rebar corrosion in concrete. Both the analytical and experimental study confirmed the capability and feasibility of the new method as a prospective quick, convenient, and quantitative solution to corrosion detection.

26 References Paulo Monteiro and Frank Morrison Non-Destructive Method of Determining the Position and Condition of Reinforcing Steel in Concrete, US Patent 5,855,721 (1999). Monteiro, P.J.M., Morrison, F., and Frangos, W., "Non-Destructive Measurement of Corrosion State of Reinforcing Steel in Concrete," ACI Materials Journal, Vol. 95, No. 6, pp , Nov- Dec Zhang, J., P.J.M. Monteiro and F. Morrison, Non-invasive surface measurement of the corrosion impedance of rebar in concrete. Part I: experimental results, ACI Materials Journal, V98 (N2): , Mar-Apr Zhang, J. and P.J.M. Monteiro, Validation of Resistivity spectra from reinforced concrete corrosion by Kramers-Kronig transformations, Cement and Concrete Research, V31, , Zhang, J., P.J.M. Monteiro, and F. Morrison, Non Invasive surface measurement of the corrosion impedance of rebar in concrete. Part II: forward modeling, ACI Materials Journal, V99 (N3): , May-June J. Zhang, P. J. M. Monteiro, and F. Morrison, M. Mancio, Non Invasive Surface Measurement of the Corrosion Impedance of Rebar in Concrete. Part III: Effect of Geometry and Material Properties, ACI materials journal, Vol 101, No. 4, 273, 2004.