Michael Thomas University of New Brunswick Chloride Specifications in Concrete Construction: Part 1 Issues & Ideas Anna Maria Workshop XVIII: Chemical Attack on Concrete, November 2017 Can Resistivity/Conductivity Measurements Really Capture Long-Term Chloride Resistance?
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Michael ThomasUniversity of New Brunswick
Chloride Specifications in Concrete Construction: Part 1 Issues & IdeasAnna Maria Workshop XVIII: Chemical Attack on Concrete, November 2017
Can Resistivity/Conductivity Measurements Really
Capture Long-Term Chloride Resistance?
1,000,000
100,000
10,000
1,000
100
10
Electrical Resistivity, 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)
1,000,000
100,000
10,000
1,000
100
10
Electrical Resistivity, 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
1500 coulombs flowing through a 95.25 dia x 50.8 mm disc in 6 hours is equivalent to: a resistivity of 121 ohm‐m, conductivity of 0.008 S/m, or a formation factor of 137/ρo (where ρo is the conductivity of the pore solution). Alternatives:
For tests where Tfinal > 50°C (122°)RCP = 12 x 30‐minute value
Electrical resistance of saturated concrete is primarily dependent on:
Ω
Electrical resistance of saturated concrete is primarily dependent on:
Pore structure• Volume, size & connectivity of
pores
Na+K+
OH-
OH- OH-
OH-Na+
K+
Electrical resistance of saturated concrete is primarily dependent on:
Pore structure• Volume, size & connectivity of
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+
Electrical resistance of saturated concrete is primarily dependent on:
Pore structure• Volume, size & connectivity of
pores
Composition of pore solution• Concentration of ions
Chloride resistance of saturated concrete is primarily dependent on:
Cl-
Cl-
Cl-
Cl-
Cl-
Na+K+
OH-
OH- OH-
OH-Na+
K+
Electrical resistance of saturated concrete is primarily dependent on:
Pore structure• Volume, size & connectivity of
pores
Composition of pore solution• Concentration of ions
Chloride resistance of saturated concrete is primarily dependent on:
Pore structure• Volume, size & connectivity of
pores Cl- Cl-Cl-
Cl- Cl-
Cl-
Cl-
Cl-
Na+K+
OH-
OH- OH-
OH-Na+
K+
Electrical resistance of saturated concrete is primarily dependent on:
Pore structure• Volume, size & connectivity of
pores
Composition of pore solution• Concentration of ions
Chloride resistance of saturated concrete is primarily dependent on:
Pore structure• Volume, size & connectivity of
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+
Electrical resistance of saturated concrete is primarily dependent on:
Pore structure• Volume, size & connectivity of
pores
Composition of pore solution• Concentration of ions
Chloride resistance of saturated concrete is primarily dependent on:
Pore structure• Volume, size & connectivity of
pores
Composition of cement hydrates• Ability of hydrates to bind
chloridesBound Cl-
Na+K+
OH-
OH- OH-
OH-Na+
K+
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
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
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
0
1000
2000
3000
4000
PC PC‐CAC‐C$ C$A‐C2S
Charged Pa
ssed
(Cou
lombs)
Binder
28‐day
91‐day
Chloride Resistance: Rapid-Set Cements
ASTM C 1202“Rapid Chloride Permeability”
PC‐CAC‐C$ 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$A‐C2S
Charged Pa
ssed
(Cou
lombs)
Binder
28‐day
91‐day
ASTM C 1202“Rapid Chloride Permeability”
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 10 20 30 40
Chlorid
e Co
nten
t (%)
Depth (mm)
PC
PC‐CAC‐C$
C$A‐C2S
ASTM C 1567“Chloride Diffusion”
Chloride Resistance: Rapid-Set Cements
F = formation factorρ = resistivity of concreteρ0 = resistivity of concrete pore solutionD = chloride diffusion coefficientDi = self diffusion coefficient for ion (= 2.032 x 10-9 m2/s for Cl-)Φ = Porosityβ = Tortuosity of pore system
Formation Factor
Formation Factor is a fundamental material property
Courtesy Jason Weiss
Resistivity of the pore solution can be
(i) assumed (e.g. ρ0 = 0.1 Ω-m [σ0 = 10 S/m] for PC mixes),
(ii) estimated (e.g. “NIST model”) – mill certs and mix proportions
(iii) measured (by pore-solution extraction)
then:
1. F could be used to specify concrete
(correcting resistivity for pore solution effects)
2. F could be used to determine D from measurement of ρ
Formation Factor
Really?
0.0
0.5
1.0
1.5
2.0
0.00 0.05 0.10 0.15 0.20 0.25 0.30(Na2Oe x CaO)/(SiO2)2 of CM
Comparison of Predicted vs Measured Values• Measurements made on pore solution pressed from hardened paste
samples at 90 days
• Predictions made using NIST ‐ https://ciks.cbt.nist.gov/poresolncalc.html
Comparison of Predicted vs Measured Values• Measurements made on pore solution pressed from hardened paste
samples at 90 days
• Predictions made using NIST ‐ https://ciks.cbt.nist.gov/poresolncalc.html
40 days
1 year
RCPTSF 1202MK 1342
RCPTSF 868MK 901
8% MK
8% SF
PC
Friedel’s Salt
Metakaolin vs. Silica Fume Bulk Diffusion Tests (C 1556)
MixBulk ρ
(KΩ.cm)RCPT
(Coulomb)
100PC 8.4 3050
25FA 23.2 1230
10SF 16.9 1630
50SG 29.7 905
Concrete Blocks (1 x 1 x 3 ft) at Treat Island in Tidal Zone for 25 years
w/cm = 0.40
No binding:
Linear isotherm:
Langmuirisotherm:
Freundlichisotherm:
100
1000
10000
10 100 1000Age (days)
RC
PT
(Cou
lom
bs)
100 PC8 SF25 FA4 SF & 20 FA
W/CM = 0.40
Time‐Dependent Changes in Electrical and Transport Properties
Diffu
sion Co
efficient (m
2 /s)
10‐10
10‐11
10‐12
10‐13
10‐14
OPC
Fly Ash
Lab ConcreteW/CM = 0.50
10 100 1000 10000 100000
Age (days)
Harmon G.S.W/CM ~ 0.58
15X reductionwith fly ash !
Bulk Diffusion (ASTM C 1556) Results for Lab & Field Concretes
M.D.A. Thomas, P.B. Bamforth/Cement and Concrete Research 29 (1999) 487–495
Taywood Blocksnr. Folkestone
Thomas & Bamforth, 1999
6 Months
0
0.1
0.2
0.3
0.4
0.5
0 20 40 60Depth (mm)
Chlo
ride
(%)
1 Year
0
0.1
0.2
0.3
0.4
0.5
0 20 40 60Depth (mm)
Chlo
ride
(%)
2 Years
0
0.1
0.2
0.3
0.4
0.5
0 20 40 60Depth (mm)
Chlo
ride
(%)
3 Years
0
0.1
0.2
0.3
0.4
0.5
0 20 40 60Depth (mm)
Chlo
ride
(%)
6 Years
0
0.1
0.2
0.3
0.4
0.5
0 20 40 60Depth (mm)
Chlo
ride
(%)
8 Years
0
0.1
0.2
0.3
0.4
0.5
0 20 40 60Depth (mm)
Chlo
ride
(%)
OPC70% Slag30% Fly Ash
Thomas & Bamforth, 1999
M.D.A. Thomas, P.B. Bamforth/Cement and Concrete Research 29 (1999) 487–495
D v t for Folkestone Blocks D v t for Lab & Field Concrete
m = 0.1
m = 0.7
m = 1.2
m = 0.12
m = 0.62
Conclusions
• Electrical resistivity/conductivity provides a good indication of the mass‐transport properties of Portland‐cement concrete
• The relationship between electrical and mass‐transport properties of concrete is strongly influenced by a number of parameters including pore‐solution conductivity
• Predicting or measuring the pore‐solution conductivity is nottrivial
• Electrical properties do not account for the interaction between chlorides and the hydrates (binding) and this can be a verysignificant factor for some binders
• Early‐age measurements of either electrical or mass‐transport properties do not capture the substantial changes that may occur with high replacement levels of pozzolans or slag