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Improved Test Methods & Practices for Characterizing Steel Corrosion
Potential of Earthen Materials
2019 Midwest Geotechnical
Engineering Conference
Crown Plaza
Columbus, Ohio
September 18, 2019
NCHRP 21-11 Update
PI : Ken Fishman, Earth Reinforcement Testing, Division of
McMahon & Mann Consulting Engineering and
Geology, P.C.
Co-PI : Soheil Nazarian, University or Texas, El Paso
1
NCHRP 21-11 WORKPLAN
• PHASE I (Tasks 1-4) – Collect Existing Information• Identify knowledge gaps
• Develop a detailed work plan to improve methods for sampling and testing and characterization of corrosiveness of earthen materials.
• PHASE II (Tasks 5 & 6) – Implement Work Plan Developed in Phase I• Study Laboratory and field tests for measurement of electrochemical
parameters, and characterizing steel corrosion
• Draft protocol for characterizing corrosiveness of earthen materials
• Formulate a detailed work plan to evaluate practical application of proposed protocol
NCHRP 21-11 WORKPLAN (Continued)
• Phase III (Tasks 7, 8 & 9) – Implement Work Plan Developed in Phase II.
• Conduct trails in active construction projects• Shadow specification to compare with current practice• Demonstrate and evaluate recommendations and protocols
for sampling, testing and characterizing corrosiveness of earthen materials.
• Initiate training with personnel from State DOTs
QUESTIONS
• How do results obtained from different test methods compare?
• How fine does the material need to be before testing the fraction passing the #10 sieve is appropriate?
• How can the test results be combined to characterize corrosion potential?
• How well does the proposed characterization of corrosion potential compare with performance?
• Is testing an aqueous extract (leachate) appropriate for coarse materials?
4
SUMMARY OF RESULTS
• Justify recommendations for draft protocol
• Comparisons between test results and identification of trends
• Comparisons between characterizations of corrosivity and performance
• Identify alternatives for coarse open graded materials
• Identify needs for further study of unconventional materials
5
Site Information/Samples
7
0%
20%
40%
60%
80%
100%
Flo
rid
a
EL
Paso
MS
E
M-U
-D N
Y
So
uth
Caro
lin
a L
WF
PIP
@ 1
5ft
PIP
@ 1
0ft
So
uth
Caro
lin
a G
B
PIP
@ 5
ft
Ph
arr
TX
Lo
usia
na L
WF
Cru
sh
ed
Ro
ch
este
r N
Y
El P
aso
TX
Cala
gary
AB
Pri
nce G
eo
rge B
C
Ash
do
wn
AR
Tem
ple
TX
Sp
rain
Bro
ok N
Y
Rale
igh
NC
Gard
en
Cit
y T
X
Map
le R
d N
Y
Wake F
ore
st
NC
Ro
un
d R
ock T
X
Lo
usia
na L
WF
Un
cru
sh
ed
Waco
TX
El P
aso
Co
ars
e M
SE
San
An
ton
io
Bastr
op
Fine Medium Coarse
Co
mp
osit
ion
, %
Material Source
Gravel Coarse Sand Fine Sand Fines
Material Composition
CONSIDERATIONS FOR SELECTION OF TEST METHODS
1. Precision and repeatability of test methods.
2. Compatibility between parameters – e.g., salt contents and resistivity
3. Correlations between resistivity measurements, corrosivity and corrosion rates
4. Utility of test results
8
Resistivity
Test Method Aggregate Size Preparation Box Size
AASHTO T288 (Standard) Passing #10Mix with 150 ml, let
stand for 12 hrs.Small
ASTM G187 As is, remove
particles greater
than ¼”
Start as is Small
ASTM WK 2461 As isSaturate and wait
24 hrs.
Small medium, or large
(depending on maximum
aggregate size)
TX-129-E (Small Box Method) Passing #8 Start dry Small
TX-129-M (Big Box Method) As is Start dry
Small medium, or large
(depending on maximum
aggregate size)
RESISTIVITY TESTS
TEST STANDARD SEPARATION MOISTURE
CONDITIONS
CURE PERIOD BIAS w.r.t.
AASHTO T-288
PRECISION
µCOV (%)
AASHTO T-288 #10 increments 12 hours for 1st
increment
- 4.6
TEX-129-E #8 increments None 1.07 3.2
ASTM G-187 ¼ inch As-is or
saturated
None 1.41 5.3
TEX-129-M none increments, but
saturated for
coarse materials
None 2.28 4.8
ASTM WK24621 none Drained from a
saturated
condition
Soak for 24
hours before
draining
3.75 7.4
10
PUBLISHED PRECISION & BIAS FOR ASTM G-187
Soil #1 Soil #2 Soil #3
Average Resistivity (Ω-cm) 2296.95 450.10 19577.14
Repeatability Standard Deviation, s, (Ω-cm) 105.78 40.82 1194.95
Repeatability Coefficient of Variation, COV, % 4.6 9.1 6.1
Reproducibility Standard Deviation, s, (Ω-cm) 318.4 40.82 1721.30
Reproducibility Coefficient of Variation, COV, % 13.9 9.1 8.8
From ILS in Tampa Florida on November 18, 2003. Triplicate soil resistivity measurements by seven participants.
11
12
y = 0.9614x
R² = 0.9543
0.0
5000.0
10000.0
15000.0
20000.0
0.0 5000.0 10000.0 15000.0 20000.0
Tex-
12
9-E
(Ω
-cm
)
AASHTO T-288 (Ω−cm)
AASHTO T-288 vs. Tex-129-E
y = 1.1484x
R² = 0.8835
0.0
5000.0
10000.0
15000.0
20000.0
0.0 5000.0 10000.0 15000.0 20000.0
AST
M G
18
7 (
Ω-c
m)
AASHTO T-288 (Ω−cm)
AASHTO T-288 vs. ASTM G 187
0.0
5000.0
10000.0
15000.0
20000.0
25000.0
30000.0
35000.0
40000.0
0.0 10000.0 20000.0 30000.0 40000.0
Tex-
12
9-M
(Ω
-cm
)
AASHTO T-288 (Ω−cm)
AASHTO T-288 vs. Tex-129-M
BIAS OF RESISTIVTY MEASUREMENTS AS A FUNCTION OF TEXTURE
0
1
2
3
4
5
6
7
Fine Sand Coarse Sand Gravel
BIA
S
MATERIALS
Tex-129-E ASTM G187 Tex-129-M ASTM WK24621
13
Effect of Texture on Resistivity
The resistivity measurements vary with respect to coarseness of the sample, especially for the TX-
620-M, TX-129-M and ASTM WK2461 test methods. In general, for the same materials, the
measurements of resistivity vary with respect to test methods, however, results from AASHTO T 288
and TX-129-E method are similar for each material.
0.0
5000.0
10000.0
15000.0
20000.0
25000.0
30000.0
35000.0
40000.0
45000.0
50000.0
AASHTO T-288 Tex-129E G-187 Tex-129M ASTM WK-2461
RE
SIS
TIV
ITY
(Ω
-cm
)
TEST METHOD
Florida
EL Paso MSE
M-U-D NY
South Carolina LWF
PIP @ 15ft
PIP @ 10ft
South Carolina GB
PIP @ 5'
Pharr TX
Rochester NY
El Paso TX
Calagary AB
Raleigh NC
Prince George BC
Temple TX
Sprain Brook NY
Maple Rd NY
Wake Forest NC
Round Rock TX
El Paso Coarse MSE
15
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
0.001 0.010 0.100 1.000
Bia
s Te
x-1
29
-M/A
AS
HTO
T-2
88
d2#10*nT288*100/(n129-M*(wg*d2
g+wcs*d2cs+wfs*d2
fs+wf*d2f))
Fine Sand
Coarse
SandGravel
TRENDING OF BIAS FROM TEX-129-M
16
Sample
Types
Bias < 1.5 1.5 < Bias < 3.0 Bias > 3
GN PP #10 GN PP #10 GN PP #10
Gravel - - 1.99 – 3.00 6- 40 3.00 – 3.56 24 - 40
Coarse
Sand
4.48- 4.83 60 - 70 3.85 - 4.48 50 - 60 - -
Fine Sand 5.00 - 6.65 > 80 - - - -
GN &PP #10 CORRESPONDING TO BIAS TRENDS
CONCLUSIONS
1. IF PP #10 > 60% then BIAS ≈ 1
2. IF GN > 3 and PP #10 < 40% then BIAS > 3
• corresponds to gravels with a coarse sand component ≈ 30%
Tests on Leachate
Test Aggregate Size Soil to Water Ratio Set up
SCDOT T143 Passing 1 ½” ~ 1:4Large plastic
container with lid
TX-620-J Passing #40 1:10Stirring plate and
stirring bar
TX-620-M Passing 1 ¾” 1:10Roller and 2-Liter
plastic bottle
MEASUREMENTS OF SULFATE CONTENT
TEST
STANDARD
SEPARATION DILUTION
RATIO
HEATED MIXING FILTRATION PRECISION
µCOV (%)
AASHTO T-290 #10 1:3 NO SHAKEN CENTRIFUGE
& FILTER
10.1
TEX-620-J #40 1:10 140°F
STIR EVERY
HOUR FOR 12
HOURS
FILTERED 11.8
TEX-620-M NONE 1:10 NO MIXED FOR
60 MINUTES
FILTERED 10.7
18
MEASUREMENTS OF CHLORIDE CONTENT
TEST
STANDARD
SEPARATION DILUTION
RATIO
HEATED MIXING FILTRATION PRECISION
µCOV (%)
AASHTO T-291 #10 1:3 NO
SHAKE
FOR 20 SEC,
STAND FOR 1
HOUR, SHAKE
CENTRIFUGE
& FILTER
7.5
TEX-620-J #40 1:10 140°F
STIR EVERY
HOUR FOR 12
HOURS
FILTERED 3.7
TEX-620-M NONE 1:10 NO MIXED FOR
60 MINUTES
FILTERED 12.9
19
20
620-M (mg/kg) = 0.71(T-290)
R² = 0.79
620-M (mg/kg) = 0.51(T-291)
R² = 0.76
0
100
200
300
400
500
600
700
800
900
1000
0 100 200 300 400 500 600 700 800 900 1000
Tex
-62
0-M
(m
g/k
g)
AASHTO T-290 & 291 (mg/kg)
Sulfate
Chloride
Linear (Sulfate)
Linear (Chloride)
CORRELATIONS BETWEEN SALT CONTENT MEASURMENTS
21
Bias = 0.06(PP#10)0.64
R² = 0.76
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
0 10 20 30 40 50 60 70 80 90 100
62
0-M
cl+
0.6
5*
62
0-M
SO
4/(
0.6
5*
T2
90
+T
29
1)
PP#10 (%)
>60%
CORRELATION BETWEEN BIAS FROM SALT CONTENT MEASUREMENTS AND PP #10
<25%
CONCLUSIONS
1. PP #10 < 25%
= lowest bias
2. PP #10 > 60%
= bias > 1
OBSERVATIONS FROM MEASUREMENTS OF SALT CONTENTS
• Precision/repeatability of test methods evaluated in this study for measurements of salt contents are similar.
• Bias statistics describing how salt contents measured via other test methods compare to those measured from the current the AASHTO tests are dependent upon material characteristics including texture as gravel, coarse sand, or fine sand.
22
23
100
1000
10000
100000
1 10 100 1000 10000
Re
sist
ivit
y (
Ω-c
m)
Equivalent Salt Content (mg/kg)
Wake Forest, NC
Ocala, FL
South Carolina LWF
Prince George, BC
Ashdown, AR
Round Rock, TX
M-U-D, NY
Raleigh, NC
South Carolina GB
Maple Road, NY
Pharr, TX
Sprain Brook NY
Garden City, TX
El Paso MSE Fine
El Paso MSE Coarse
El Paso, TX
Rochester, NY
Calgary, AB
Temple, TX
PIP, NY @ 15 feet
Louisiana LWF Uncrushed
Bastrop, TX
Louisiana LWF Crushed
Waco, TX
Chloride
minus 25 % error
plus 25% error
Equivalent Salt Content vs. Resistivity
with
AASHTO (PP #10 > 22%) or Texas Modified (PP#10 < 22%)
Wake
RR
GCEl Paso – MSE Coarse
24
y = 142105x-1.1
R² = 0.88
100.00
1000.00
10000.00
100000.00
0.01 0.10 1.00 10.00 100.00
Re
sist
ivit
y Te
x-6
20
-M (
Ω-c
m)
Total Salt Content Tex-620-M (mEq)
y = 13488x-0.82
R² = 0.64
100.0
1000.0
10000.0
100000.0
1.00 10.00 100.00R
esi
stiv
ity
AA
SH
TO
T-2
88
(Ω-c
m)
Total Salt Content AASHTO (mEq)
Total Salt (mEq) = ppm ÷ equiv. atomic weight = Cl-(kg/mg) ÷ 35.5 + SO4 (kg/mg) ÷ 48. + HCO3 (kg/mg)÷ 61
CORRELATION BETWEEN TOTAL SALT CONTENT
and RESISTIVITY MEASUREMENTS
pH MEASURMENTS
TEST
STANDARD
AIR
DRY
SEPARATION DILUTION
RATIO
HEATED MIXING STAND
TIME
PRECISION
µCOV (%)
AASHTO T-289 Y #10 1:1 N Stir every 10-15 min
for 1 hour
NONE 1.0
ASTM D 4972 Y #10 1:1 N Mix thoroughly 1 HR 1.1
NCHRP 21-06 N 3/8 IN 1:1 N Stirred 30 MIN 0.7
TEX-129-E Y #40 1:5 Y Stir every 15 min. for
1 hour
NONE 0.9
TEX-620-M Y NONE 1:10 N Agitate for 1 hour NONE 1.2
25
26
21-06 = 0.98 (T-289)
R² = 0.70
5.0
6.0
7.0
8.0
9.0
10.0
5.0 6.0 7.0 8.0 9.0 10.0NC
HR
P 2
1-0
6 (
pH
)
AASHTO T-289 (pH)
D 4972 = 0.99(T-289)
R² = 0.69
5.0
6.0
7.0
8.0
9.0
10.0
5.0 6.0 7.0 8.0 9.0 10.0
AST
M D
49
72
(p
H)
AASHTO T-289 (pH)
128-E = 1.03(T-289)
R² = 0.63
5.0
6.0
7.0
8.0
9.0
10.0
5.0 6.0 7.0 8.0 9.0 10.0
Tex-
12
8-E
(p
H)
AASHTO T-289 (pH)
Tex-620-M = 1.08(T-289)
R² = 0.33
5.0
6.0
7.0
8.0
9.0
10.0
5.0 6.0 7.0 8.0 9.0 10.0
Tex-
62
0-M
(p
H)
AASHTO T-289 (pH)
COMPARISON of pH MEASURMENTS RELATIVE TO AASHTO T-289
27
0
2
4
6
8
10
1.03 1.05 1.07 1.10 1.12 More
Fre
qu
en
cy
Bias - Tex-620-M/AASHTO T-289
CONCLUSIONS• Measurements of pH from Tex-620-M are less repeatable compared to measurements from
other test standards.
• In general, Tex-620-M renders pH that are higher compared to the pH values from the other
test standards included in the study.
• Results from NCHRP 21-06 are more repeatable compared to AASHTO T-289 and do not
have a significant bias with respect to results from AASHTO T-289.
DISTIBUTION of BIAS FROM pH MEASURMENTS
28
CR = 2877ρ-0.73
R² = 0.50
0
5
10
15
20
25
30
35
40
45
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Co
rro
sio
n R
ate
(µ
m/y
r)
Resistivity (Ω-cm)
Ocala, FL
South Carolina LWF
Ashdown, AR
M-U-D, NY
Raleigh, NC
South Carolina GB
El Paso, TX
Rochester, NY
Sprain Brook NY
El Paso MSE Fine
PIP, NY @ 15 feet
Power (Trendline)
CR = 5267ρ-0.84
R² = 0.62
0
5
10
15
20
25
30
35
40
0 10000 20000 30000 40000 50000
Me
asu
red
CR
(µm
/yr)
Resistivity (Ω-cm)
CORROSION RATES & RESISTIVITY MEASUREMENTS FROM
AASHTO T-288 WITH > 22% PASSING #10
Data from NCHRP 21-11
Worldwide Data
PROPOSED PROTOCOL
1. IF GN > 3 or PP #10 > 25%
• AASHTO T-288, T-289, T-290 & T-291
2. IF GN < 3 and PP # 10 < 25%
• Tex-129-M, Tex-620-M
• ??? Considering using NCHRP 21-06 for pH ???
3. Consider alternatives for very coarse, open graded material
29
Summary of Screening Techniques and Characterizations
UNIVARIATE – Binary Systems MULTIVARIATE1. AASHTO (1992) - Galvanized Steel 1. German DVGW GW 9 –Pipelines
2. PTI – Prestressing Steel (High Strength) 2. AWWA (DIP) – 10 Point Method
3. Burec (2009) Resistivity - 10th Percentile – DIP
and CIP
3. Jones (1985) – steel soil reinforcements
4. FHWA (2003) – Solid Bar Soil Nails – Carbon
Steel
4. Clouterre (1993) – Soil Nails
5. European Standard – EN 12501-2 (2003) 5. Brady and McMahon (1994), UK – Galvanized
steel structures/Culverts
6. Beavers and Durr (1998), NACE (2001) – Steel
Piles
7. AGA (1983) – Hot-dipped Galvanized Steel
8. Demisse (2015) - Bayes Network - waterlines 30
Parameter AASHTO Test
Method
Requirement
ρmin T 288 >3000 Ω-cm
pH T 289 5 to 10
Sulfates T 290 <200 ppm
Chlorides T 291 <100 ppm
AASHTO Electrochemical
Requirements for Mechanically
Stabilized Earth Fill Used with
Galvanized Steel
Reinforcements
Criteria Used in
the US for
Assessing Ground
Corrosion
Potential Relative
to SBSN’s (after
FHWA, 2003)
31
German Gas and Water Works Engineers’ Association Standard (DVGW GW9)
32
ITEM MEASURED VALUE MARKS
Soil
Composition
Calcareous, marly limestone, sandy marl,
not stratified sand
+2
Loam, sandy loam (loam content 75% or
less), marly loam, sandy clay soil (silt
content 75% or less)
0
Clay, marly clay, humus -2
Peat, thick loam, marshy soil -4
Ground water
level at buried
position
None 0
Exist -1
Vary -2
Resistivity
> 10,000 Ω-cm 0
5000 Ω-cm – 10,000 Ω-cm -1
2300 Ω-cm – 5000 Ω-cm -2
1000 Ω-cm – 2300 Ω-cm -3
> 10000 Ω-cm -4 33
ITEM MEASURED
VALUE
MARKS
Moisture Content 20% or less 0
20% or more -1
pH 6 or more 0
6 or less -2
Sulfide and
Hydrogen Sulfide
None 0
Trace -2
Exist -4
Carbonate
5% or more +2
1% to 5% +1
< 1% 0
Chloride
< 100 ppm 0
> 100 ppm -1
34
ITEM MEASURED VALUE MARKS
Sulfate
< 200 ppm 0
500 ppm – 200 ppm -1
1000 ppm – 500 ppm -2
> 1000 ppm -3
Cinder
& Coke
None 0
exist -4
SCORE CHARACTERIZATION
> 0 Noncorrosive
0 to -4 Slightly Corrosive
-5 to -10 Corrosive
< -10 Very Corrosive
DVGW GW9 –
Characterization of Corrosivity
35
Total
Score
General
Corrosion
Rate
Range Localized
(Pitting)
Corrosion
Rate
Range
µm/yr µm/yr
≥ 0 Ia 5 2.5 – 10 30 15 – 60
-1 to -4 Ib 10 5 – 20 60 30 – 120
-5 to -10 II 20 10 – 40 200 100 – 400
< -10 III 60 30 - 120 400 200 - 800
Soil Corrosivity/Aggressiveness
(Carbon Steel) DIN 50 929 Part 3
36
37
Sample GN #10 Test
Method
(Proposed
Protocol)
Corros.
RankA
(I)
CR
(µm/yr)
Cluster
Galv. Plain
San Antonio, TX 0.18 2 Tex-129-M 1.0 NAB
No
t Co
rrosiv
e
(I) ≥
0
Wake Forest, NC 2.21 8 Tex-129-M 2 0.3 < 0.1
Bastrop, TX 0.15 2 Tex-129-M 2 0.4 NA
Ashdown, AR 2.88 36 AASHTO T-288 2 1.8C NA
TTC, NC 3.51 24 AASHTO T-288 1 5.8 1.6
Ocala, FL 5.65 91 AASHTO T-288 0 1.8 3.8
LWF, South
Carolina
4.83 68 ASTM
WK 24261
0 1.2 8.4
El Paso
Coarse/MSE
0.22 2 Tex-129-M 0 0.2 NA
Waco, TX 1.26 7 Tex-129-M 0 0.3 NA
M-U-D, NY 5.24 82 AASHTO T-288 -1 4.8 39 Slig
htly
Co
rrosiv
e
-3 ≤
(I) <
0
Garden City, TX 2.52 22 Tex-129-M -1 4.3 NA
GB, South Carolina 4.48 56 AASHTO T-288 -1 3.2D 5.8
Maple Rd., NY 2.50 22 Tex-129-M -2 3.7 16
El Paso Fine/MSE 5.52 87 AASHTO T-288 -2 21E NA
Prince George, BC 2.89 32 AASHTO T-288 -3 NA 20
PIP, NY 4.62 61 AASHTO T-288 -4 37 30
Co
rrosiv
e
-5 ≤
(I) <
-3
Sprain Brook Pkwy,
NY
2.54 27 AASHTO T-288 -4 33 NA
Quarry; El Paso, TX 3.64 41 AASHTO T-288 -4 14.8 NA
Rochester, NY 3.85 49 AASHTO T-288 -5 9.6 20
Data Clustering Relating
Corrosivity Rankings to
Observed Rates of
Corrosion
Corrosivity Clusters Observed Corrosion Rates, CR
Galvanized Plain Steel
(I) ≥ 0 CR < 2 µm/yr CR < 5 µm/yr
-3 ≤ (I) < 0 2 µm/yr < CR < 5 µm/yr 5 µm/yr < CR < 20 µm/yr
-5 ≤ (I) < -3 10 µm/yr < CR < 35 µm/yr 20 µm/yr < CR < 40 µm/yr
NCHRP 21-11 – PHASE III
• Phase III (Tasks 7, 8 & 9) – Implement Work Plan Developed in Phase II.
• Conduct trials in active construction projects• Shadow specification to compare with current practice• Demonstrate and evaluate recommendations and protocols
for sampling, testing and characterizing corrosiveness of earthen materials.
• Initiate training with personnel from State DOTs
38
Conduct Field Tests to Support Recommended Specifications for New
Methodology
• Identify fill source prior to construction
• Relevant activities include:• Sampling the materials before construction
• Sampling the materials during compaction
• Conducting field resistivity for comparison to the lab resistivity
• Conducting moisture-density tests with help of DOT
• Conduct index and electrochemical tests on:• Materials collected before construction
• Materials collected during construction
39
Insitu Soil Testing
Calgary, AB
Marcy – Utica – Deerfield, NY
• Stevens Hydraprobe uses a five-tine probe
that can measure the subsurface moisture
content and conductivity which can be
converted into resistivity
• The Wenner 4-electrode method (ASTM G-57)
measures the resistivity of the subsurface by
inserting 4 equally spaced electrodes into
the ground in a line, applying an electric
current between two outer electrodes, and
measuring the corresponding voltage drop
between the inner electrodes.
COARSE GRAINED SAMPLE AT SATURATION
41
REMARKS
• Consistent trends are observed between results obtained with different test methods and between materials with different textures
• Salt contents are a good check on measured resistivity
• AASHTO Test Methods apply well to materials with more than 25% passing the #200 sieve.
• TX-129-M and TEX-620-M apply well to coarse materials
• Results from TX-129-M and TEX-620-M can be correlated
• Good correlation between observed performance (CR’s) and characterization of corrosion potential based on resistivity measurements.