PCA R&D Serial No. 2821a Electrical Methods for Estimating the … · 2014. 4. 14. · 91-day Chloride Resistance: Rapid-Set Cements. ASTM C 1202 “Rapid Chloride Permeability”

Electrical Methods for Estimating the Chloride Resistance of Concrete

Michael Thomas, Ted Moffatt & Huang YiUniversity of New Brunswick

David E. SmithLevelton 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

PCA R&D Serial No. 2821a

Electrical Methods for Estimating theChloride Resistance of Concrete

• Resistivity• Conductivity • “Chloride Permeability”

• Migration tests• Chloride flux• Breakthrough

• Rapid migration test

txx

zFURTLD dd

nssm

α−⋅=

RTzFECDJ fx ⋅=

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

IVR =

lAR ⋅=ρ

ρRVIAl

= resistivity (Ω∙m)= resistance (Ω)= potential (Volts)= current (Amps)= sample area (m2)= sample length (m)

Electrical Conductivity, σ (S/m)

ρσ 1=


50 mm

100 mm

3 to 5 V

D.C. Resistivity

Cycle voltage between 3 and 5 volts every 5 seconds for 15 minutes:

( )( ) LII

AVV⋅−⋅−

=35

35ρ

ρ = resistivity (Ω-cm)I5 = current (Amps) at V5 voltsI5 = current (Amps) at V5 voltsA = cross-sectional area (cm2)L = length (cm)


ASTM C 1760 Bulk Conductivity of Concrete

NaO

HNaC

lV I

⋅

=

ld

IV

4

2πρ

where: ρ = resistivity in Ω-mV = applied voltage, VI = current, Ad = specimen diameter, ml = specimen length, m

Electrical Resistivity

Electrical Conductivity 21

DL

VIK ⋅=σ

The SI unit for electrical conductivity is siemens/metre

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°Cor 7d at 23°C & 21d at 38°C


4-Point Probe

IVa ⋅= πρ 2




1,000,000

100,000

10,000

1,000

100

10

Elec

tric

al R

esist

ivity

, ρ(Ω

∙m)

Concrete (oven-dry)

Concrete (dry-indoors)

Concrete (dry-outdoors)

Concrete (saturated)

Range of values forsaturated concrete

10-8 Copper

1014 Neoprene Rubber

0.001

0.01

0.1

1

10

100

Electrical Conductivity, σ(m

S/m)

ASTM C 1760 (2012)“Bulk Conductivity”

Adapted from Whiting & Nagi, 2003

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)


Electrical resistance of saturated concrete is primarily dependent on:

Ω



Pore structure• Volume, size & connectivity of

pores


Na+K+

OH-

OH- OH-

OH-Na+

K+



pores

Composition of pore solution• Concentration of ions

More ions in solution – increased electrical conductivity – i.e. reduced electrical resistance


Na+K+

OH-

OH- OH-

OH-Na+

K+



pores


Chloride resistance of saturated concrete is primarily dependent on:

Cl-

Cl-

Cl-

Cl-

Cl-


Na+K+

OH-

OH- OH-

OH-Na+

K+



pores




pores Cl- Cl-Cl-

Cl- Cl-

Cl-

Cl-

Cl-


Na+K+

OH-

OH- OH-

OH-Na+

K+



pores




pores

Composition of cement hydrates• Ability of hydrates to bind

chlorides

Cl-

Cl-Cl-

Cl-

Cl-

Cl-

Cl-

Cl-


Cl-

Cl-Cl-

Cl-

Cl-

Cl-

Cl-

Cl-

Na+K+

OH-

OH- OH-

OH-Na+

K+



pores




pores

Composition of cement hydrates• Ability of hydrates to bind

chloridesBound Cl-


Na+K+

OH-

OH- OH-

OH-Na+

K+



pores


Hydraulic conductivity is primarily dependent on:


pores


Chl

orid

e (%

)

Depth (mm)

CC

erfxD t

x

a01

2= −

⋅

Co and Da found by fitting the equation

shown to the measured profile.

Concrete sample is immersed in NaCl solution for time t (minimum 35 days)Sample then ground in approx. 1-mm depth incrementsDust samples analyzed for chlorides →To produce chloride profile ↓

ASTM C 1556 Test to Determine the Bulk Diffusion Coefficient of Concrete

Values of Da typically in the range:1 x 10-13 to 1 x 10-11 m2/s


100

1000

10000

100000

1.E-13 1.E-12 1.E-11 1.E-10

RC

PT (C

oulo

mbs

)

Diffusion Coefficient (m2/s)

RCPT vs. Bulk Diffusion

1000Coulombs

10-12 to 10-11


100

1000

10000

100000

1 10 100 1000

RC

P (C

oulo

mbs

)

Resistivity (kΩ-cm)

RCPT vs. Electrical ResistivityPCA R&D Serial No. 2821a


Concrete International, Nov 2011

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)


25-Year-OldMarine-ExposedConcrete Blocks

1

10

100

1000

0.1 1 10 100

Surf

ace

Resis

tivity

, ρ (Ω

∙m)

Diffusion Coefficient, D (x10-12 m2/s)

65% Slag

45% Slag

25% Slag

0% Slag


10

100

1,000

Resi

stiv

ity, ρ

(Ω-m

)

• Degree of saturation• Self-desiccation• Drying

• Leaching

• Chloride ingress

• Carbonation

• Rebar

1 20

Stored in 1% CO2 (60% RH)Resaturated before test

Stored in N2 (60% RH)Resaturated before test

Cycles

Factors Affecting ResistivityPCA R&D Serial No. 2821a

0

50

100

150

200

10 100 1000 10000

Resis

tivity

, ρ (Ω

-m)


• Leaching


• Carbonation

• Rebar

Age (days)

Stored in tap water

Stored in “model” pore solution

Factors Affecting Resistivity

Tests conducted on mortar cubes



• Leaching


• Carbonation

• Rebar

Age (days)

0

50

100

150

200

10 100 1000 10000

Resis

tivity

, ρ (Ω

-m) Insitu surface

measurements

Tests on cores



• Leaching


• Carbonation

• Rebar


0.0

2.0

4.0

6.0

0

100

200

300

50 60 70 80 90

Diffusion Coefficient (x 10-12m

2/s)Re

sistiv

ity, ρ

(Ω-m

)

Aggregate Volume, Va (%)

= resistivity of matrix= resistivity of composite= resistivity of aggregate= volume fraction

of aggregate

Maxwell’s Eqn:

Resistivity

Diffusion

Effect of Paste ContentPCA R&D Serial No. 2821a

0

1000

2000

3000

4000

PC PC-CAC-C$ C$A-C2S

Char

ged

Pass

ed (C

oulo

mbs

)

Binder

28-day

91-day

Chloride Resistance: Rapid-Set Cements

ASTM C 1202“Rapid Chloride Permeability”

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


0

1000

2000

3000

4000

PC PC-CAC-C$ C$A-C2S

Char

ged

Pass

ed (C

oulo

mbs

)

Binder

28-day

91-day

ASTM C 1202“Rapid Chloride Permeability”

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 10 20 30 40

Chlo

ride

Cont

ent (

%)

Depth (mm)

PC

PC-CAC-C$

C$A-C2S

ASTM C 1567“Chloride Diffusion”

Chloride Resistance: Rapid-Set CementsPCA 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


Documents

PCA R&D Serial No. 2821a Electrical Methods for Estimating the … · 2014. 4. 14. · 91-day Chloride Resistance: Rapid-Set Cements. ASTM C 1202 “Rapid Chloride Permeability”