PCA R&D Serial No. 2821a
Electrical Methods for Estimating the Chloride
Resistance of Concrete
Michael Thomas, Ted Moffatt & Huang Yi
University of New Brunswick
David E. Smith
Levelton Consultants Ltd.
Electrical Methods for Characterization and Monitoring of
Concrete Materials and Structures
ACI Fall 2013 Convention, October 2013, Phoenix, AZ
Co-Sponsored by ACI 222, 228, ACI-ASCE 444
Electrical Methods for Estimating the
Chloride Resistance of Concrete
PCA R&D Serial No. 2821a
• Resistivity
• Conductivity
• “Chloride Permeability”
• Migration tests
• Chloride flux
• Breakthrough
J = D fx C ⋅
• Rapid migration test
RTL xd − α xd
⋅
Dnssm =
zFU
t
zFE
RT
Stanish, K.D., Hooton, R.D., and
Thomas, M.D.A., 2001, Prediction
of Chloride Penetration in
Concrete, US Department of
Transportation, Federal Highway
Administration, Publication No.
FHWA-RD-00-142.
Measuring Electrical Resistivity, ρ
PCA R&D Serial No. 2821a
V
R=
I
A
ρ = R⋅
l
ρ = resistivity (Ω∙m)
R
V
I
A
l
= resistance (Ω)
= potential (Volts)
= current (Amps)
= sample area (m2)
= sample length (m)
Electrical Conductivity, σ (S/m)
σ=
1
ρ
PCA R&D Serial No. 2821a
D.C. Resistivity
3 to 5 V
Cycle voltage between 3 and 5 volts
every 5 seconds for 15 minutes:
(
V5 − V3 ) ⋅ A
ρ=
(I 5 − I 3 ) ⋅ L
100 mm
50 mm
ρ = resistivity (Ω-cm)
I5 = current (Amps) at V5 volts
I5 = current (Amps) at V5 volts
A = cross-sectional area (cm2)
L = length (cm)
PCA R&D Serial No. 2821a
ASTM C 1760 Bulk Conductivity of Concrete
V
V
ρ
=
Electrical Resistivity

I
I
NaOH
NaCl
where:
ρ = resistivity in Ω-m
V = applied voltage, V
I = current, A
d = specimen diameter, m
l = specimen length, m
ASTM C 1760
•
Cylinders 100 x 200 mm
•
Cores ≥ 100 mm long
•
PC cure for 28 days at 23°C
•
SCM cure for 56 days at 23°C
or 7d at 23°C & 21d at 38°C
2
  πd 

 ⋅ 
  4l 
Electrical Conductivity
I1 L
σ =K ⋅ 2
V D
The SI unit for electrical conductivity is siemens/metre
4-Point Probe
V
ρ = 2πa ⋅
I
PCA R&D Serial No. 2821a
PCA R&D Serial No. 2821a
PCA R&D Serial No. 2821a
1014
Electrical Resistivity, ρ (Ω∙m)
PCA R&D Serial No. 2821a
ASTM C 1760 (2012)
“Bulk Conductivity”
Concrete (oven-dry)
0.001
100,000
0.01
10,000
0.1
Concrete (dry-indoors)
1,000
100
10
10-8
1
Concrete (dry-outdoors)
Concrete (saturated)
Copper
Adapted from Whiting & Nagi, 2003
Range of values for
saturated concrete
10
100
Electrical Conductivity, σ (mS/m)
1,000,000
Neoprene Rubber
If ρ = 182 Ω∙m (σ = 5.5 mS/m) the charge
passed through a standard-size specimen
(φ3.75-in. x 2-in.) in the “Rapid Chloride
Permeability Test” (ASTM C 1202) would be
approximately 1000 Coulombs (6h at 60V)
PCA R&D Serial No. 2821a
Electrical resistance of saturated concrete
is primarily dependent on:
Ω
PCA R&D Serial No. 2821a
Electrical resistance of saturated concrete
is primarily dependent on:

Pore structure
•
Volume, size & connectivity of
pores
PCA R&D Serial No. 2821a
Electrical resistance of saturated concrete
is primarily dependent on:

Pore structure
•

Volume, size & connectivity of
pores
K+
OHOH-
K+
OH-
Na+
OH-
Na+
Composition of pore solution
•
Concentration of ions
More ions in solution – increased
electrical conductivity – i.e. reduced
electrical resistance
PCA R&D Serial No. 2821a
Electrical resistance of saturated concrete
is primarily dependent on:

Pore structure
•

Volume, size & connectivity of
pores
OH-
Composition of pore solution
•
K+
OH-
Concentration of ions
Chloride resistance of saturated concrete
is primarily dependent on:
ClClClClCl-
K+
Na+
OH-
Na+
OH-
PCA R&D Serial No. 2821a
Electrical resistance of saturated concrete
is primarily dependent on:

Pore structure
•

K+
OH-
Volume, size & connectivity of
pores
OH-
OH-
K+
Na+
OH-
Na+
Composition of pore solution
•
Concentration of ions
Chloride resistance of saturated concrete
is primarily dependent on:

Pore structure
•
Volume, size & connectivity of
pores
ClCl-
ClCl-
Cl-
Cl-
Cl-
Cl-
PCA R&D Serial No. 2821a
Electrical resistance of saturated concrete
is primarily dependent on:

Pore structure
•

Volume, size & connectivity of
pores
OH-
K+
Na+
OH-
Na+
Composition of pore solution
•
Concentration of ions
Chloride resistance of saturated concrete
is primarily dependent on:


Cl-
Pore structure
•
Volume, size & connectivity of
pores
Composition of cement hydrates
•
Ability of hydrates to bind
chlorides
K+
OH-
ClCl-
ClCl-
ClClCl-
OH-
PCA R&D Serial No. 2821a
Electrical resistance of saturated concrete
is primarily dependent on:

Pore structure
•

Volume, size & connectivity of
pores
OH-
K+
Na+
OH-
Na+
Composition of pore solution
•
Concentration of ions
Chloride resistance of saturated concrete
is primarily dependent on:


Cl-
Pore structure
•
Volume, size & connectivity of
pores
Composition of cement hydrates
•
Ability of hydrates to bind
chlorides
K+
OH-
ClCl-
ClCl-
ClClCl-
Bound Cl-
OH-
PCA R&D Serial No. 2821a
Electrical resistance of saturated concrete
is primarily dependent on:

Pore structure
•

Volume, size & connectivity of
pores
Composition of pore solution
•
Concentration of ions
Hydraulic conductivity is primarily
dependent on:

Pore structure
•
Volume, size & connectivity of
pores
K+
OHOH-
K+
Na+
OH-
Na+
OH-
PCA R&D Serial No. 2821a
ASTM C 1556 Test to Determine the Bulk Diffusion Coefficient of Concrete
Chloride (%)
Concrete sample is immersed in NaCl solution
for time t (minimum 35 days)
Sample then ground in approx. 1-mm depth
increments
Dust samples analyzed for chlorides →
To produce chloride profile ↓

x 
Cx

= 1 − erf 
C0
 2 Da ⋅ t 
Co and Da found by fitting the equation
shown to the measured profile.
Values of Da typically in the range:
1 x 10-13 to 1 x 10-11 m2/s
Depth (mm)
PCA R&D Serial No. 2821a
RCPT vs. Bulk Diffusion
RCPT (Coulombs)
100000
10-12 to 10-11
10000
1000
1000
Coulombs
100
1.E-13
1.E-12
1.E-11
Diffusion Coefficient (m2/s)
1.E-10
PCA R&D Serial No. 2821a
RCPT vs. Electrical Resistivity
RCP (Coulombs)
100000
10000
1000
100
1
10
Resistivity (kΩ-cm)
100
1000
PCA R&D Serial No. 2821a
PCA R&D Serial No. 2821a
Superior performance of concrete with SCM at Treat Island has been confirmed for fly ash,
slag and silica fume (and ternary cement blends with silica fume plus fly ash)
Concrete International, Nov 2011
PCA R&D Serial No. 2821a
25-Year-Old
Marine-Exposed
Concrete Blocks
1000
Surface Resistivity, ρ (Ω∙m)
65% Slag
45% Slag
100
25% Slag
0% Slag
10
1
0.1
1
10
100
Diffusion Coefficient, D (x10-12 m2/s)
PCA R&D Serial No. 2821a
Factors Affecting
Resistivity
• Degree of saturation
•
•
Self-desiccation
Drying
1,000
• Chloride ingress
• Carbonation
• Rebar
Resistivity, ρ (Ω-m)
• Leaching
Stored in 1% CO2 (60% RH)
Resaturated before test
100
Stored in N2 (60% RH)
Resaturated before test
10
0
1
Cycles
2
PCA R&D Serial No. 2821a
Factors Affecting
Resistivity
• Degree of saturation
•
•
Self-desiccation
Drying
200
Tests conducted on mortar cubes
• Chloride ingress
• Carbonation
• Rebar
Resistivity, ρ (Ω-m)
• Leaching
150
Stored in tap water
100
Stored in “model”
pore solution
50
0
10
100
1000
Age (days)
10000
PCA R&D Serial No. 2821a
Factors Affecting
Resistivity
• Degree of saturation
•
•
Self-desiccation
Drying
200
• Chloride ingress
• Carbonation
• Rebar
Resistivity, ρ (Ω-m)
• Leaching
Insitu surface
measurements
150
100
Tests on cores
50
0
10
100
1000
Age (days)
10000
• Degree of saturation
•
•
Self-desiccation
Drying
• Leaching
• Chloride ingress
• Carbonation
• Rebar
PCA R&D Serial No. 2821a
Factors Affecting
Resistivity
PCA R&D Serial No. 2821a
Effect of Paste Content
Resistivity, ρ (Ω-m)
6.0
Diffusion
200
4.0
Resistivity
Maxwell’s Eqn:
100
0
50
60
2.0
= resistivity of matrix
= resistivity of composite
= resistivity of aggregate
= volume fraction
of aggregate
70
80
Aggregate Volume, Va (%)
0.0
90
Diffusion Coefficient (x 10-12 m2/s)
300
PCA R&D Serial No. 2821a
Chloride Resistance: Rapid-Set Cements
ASTM C 1202
“Rapid Chloride Permeability”
Charged Passed (Coulombs)
4000
28-day
91-day
3000
2000
PC-CAC-C$ is a ternary blend of:
• Portland cement
• Calcium-aluminate cement
• Gypsum
CSA-C2S is a blend of:
• Calcium-alumino-sulfate
(Klein’s compound)
• Belite
1000
0
PC
PC-CAC-C$ C$A-C2S
Binder
PCA R&D Serial No. 2821a
Chloride Resistance: Rapid-Set Cements
ASTM C 1202
“Rapid Chloride Permeability”
ASTM C 1567
“Chloride Diffusion”
1.2
28-day
91-day
3000
2000
1000
Chloride Content (%)
Charged Passed (Coulombs)
4000
PC
1.0
PC-CAC-C$
C$A-C2S
0.8
0.6
0.4
0.2
0.0
0
PC
PC-CAC-C$ C$A-C2S
Binder
0
10
20
30
Depth (mm)
40
PCA R&D Serial No. 2821a
Smith, D. 2004. “The Development of a Rapid Test for Determining the
Transport Properties of Concrete.” M.Sc.E. Thesis, University of New Brunswick