important aspects of chemical stabilization of fine ... · pdf fileimportant aspects of...
TRANSCRIPT
Important Aspects of Chemical Stabilization of Fine-Grained Soils
Amy B. Cerato, Ph.D., P.E. and
Gerald A. Miller, Ph.D., P.E.School of Civil Engineering and Environmental Science
University of Oklahoma
2014 SPTC Seminar SeriesOklahoma City, OK
April 24, 2014
4/24/2014 1
Acknowledgements
• Steve Sawyer and ODOT Training Center for hosting
• ODOT for supporting research
• Donald Snethen – research partner, mentor, and slide contributor
• SPTC for support, especially Sonya Brindle
4/24/2014 2
Outline
1. The state of the practice relative to selecting a stabilizer and determining the optimum additive content based on soil properties– Chemical additives– Chemical treatment basics– Modification versus stabilization– Improvements in treated soil behavior– Relevant documents and standards
• ODOT 2009 Standard Specifications, Section 307• OHD L-49, OHD L-50, OHD L-51• ASTM D4609, ASTM D6276
4/24/2014 3
Outline
2. Adverse reactions and unexpected outcomes from chemical stabilization
– Sulfate bearing soil
– Post-construction wetting
– Laboratory versus field testing
– Other problems
4/24/2014 4
Outline
3. Determination of the additive content of compacted soils in the field
– Qualitative methods – pH based
– Quantitative lab methods
– X-ray fluorescence (XRF)
4/24/2014 5
1. The state of the practice relative to selecting a stabilizer and determining the optimum additive content based on soil properties– Chemical additives– Chemical treatment basics– Modification versus stabilization– Improvements in treated soil behavior– Relevant documents and standards
• ODOT 2009 Standard Specifications, Sections 307 and 700• OHD L-49, OHD L-50, OHD L-51• ASTM D4609, ASTM D6276
4/24/2014 6
• Common Chemical Additives
– Cementitious
• Cement
• Fly Ash
• Cement Kiln Dust (CKD)
– Non-cementitious
• Lime
*Lime can promote cementation via pozzolanic reactions under the right conditions
4/24/2014 7Chemical Additives
• Chemical Compositions (most components)
– Sources
• Lime – National Lime Association
• Flyash and Portland Cement – FHWA-IF-03-019
• CKD – Miller et al. 2000 (via manufacturers)
Item(%)
LimeClass C Fly Ash
Class F Fly Ash
Portland Cement
CKD 1 CKD 2 CKD 3
SiO2 <1 40 55 23 12 15 16
Al2O3 <1 17 26 4 5 4 4
FE2O3 <1 6 7 2 2 2 2
CaO 95 24 9 64 42 45 53
MgO 2 5 2 2 1 1 2
SO3 --- 3 1 2 7 3 6
K2O 2 2 4
LOI --- <5 <5 --- 24 28 18
Chemical Additives4/24/2014 8
1. The state of the practice relative to selecting a stabilizer and determining the optimum additive content based on soil properties– Chemical treatment basics– Chemical additives– Modification versus stabilization– Improvements in treated soil behavior– Relevant documents and standards
• ODOT 2009 Standard Specifications, Sections 307 and 700• OHD L-49, OHD L-50, OHD L-51• ASTM D4609, ASTM D6276
4/24/2014 9
Chemical Treatment Basics
• Basic Soil-Additive Chemical Interactions– Cation exchange
– Flocculation/agglomeration
– Pozzolanic reactions
– Cementation
– Carbonation
*Extent of these interactions depends on additive and soil composition
*Important to match additive to soil type!
4/24/2014 10
• Cation exchange
– Ca2+ released from additive in presence of H2O
– Ca2+ adsorbed by soil particle diffuse double layer
• Exchanges with lower valence cations (e.g. Na+)
• Reduce soil particle electrical potential
Chemical Treatment Basics4/24/2014 11
• Flocculation/Agglomeration
– Caused by change in pH, cation exchange and increased electrolyte concentration in pore water
Results:• Contraction of diffuse double layer• Soil particles flocculate and “clump” together (increased
edge to face associations)• Plasticity decreases• Workability increases
Reactions occur rapidly
C.E. and F/A are basis for chemical modification.
Chemical Treatment Basics4/24/2014 12
Dispersed Structure
Add chemical
Add water
Mix
Flocculated/Agglomerated
Structure
Chemical Treatment Basics4/24/2014 13
• Pozzolanic Reaction Products (PRPs)– Water added and calcium provided by chemical
additive
– Increase in pH soil releases silica and alumina
– Combine to form cementing-type materials• Calcium-silicate-hydrates, CSHs• Calcium-aluminate-hydrates, CAHs
– Extent depends on Time, Temperature, pH– PRPs increase strength and basis for chemical
stabilization.
Chemical Treatment Basics4/24/2014 14
Pozzolanic Reaction Products
4/24/2014 15Chemical Treatment Basics
Untreated shale Shale w/llime – 28 days
• Cementation
– Occurs with intrinsically cementitious additives
– Soil does not need to contribute to formation of CSHs and CAHs, as with lime
• i.e., reason lime does not work with sand, while CKD, Fly Ash and Cement will
Chemical Treatment Basics4/24/2014 16
4/24/2014 17Chemical Treatment Basics
Untreated shale Shale w/llime – 28 days
Shale w/CKD – 28 daysCuring Time (days)
0 10 20 30 40 50 60 70 80 90 100
UC
S (
psi)
0
50
100
150
200
250
300
350
Untreated
Lime
CKD
• Carbonation
– Reaction of calcium-based products with carbon dioxide in atmosphere producing calcium carbonate.
– Undesirable reaction that retards development of CSHs and CAHs.
* Proper storage and handling important!
Chemical Treatment Basics4/24/2014 18
• Factors that adversely influence soil-chemical reactions:
– Organic carbon content of soil
– Excessive quantities of exchangeable sodium
– Presence of carbonates and phosphates in soil
– Presence of sulfates in soil
Chemical Treatment Basics4/24/2014 19
1. The state of the practice relative to selecting a stabilizer and determining the optimum additive content based on soil properties– Chemical treatment basics– Chemical stabilizers– Modification versus stabilization– Improvements in treated soil behavior– Relevant documents and standards
• ODOT 2009 Standard Specifications, Sections 307 and 700• OHD L-49, OHD L-50, OHD L-51• ASTM D4609, ASTM D6276
4/24/2014 20
1. Modification
Addition of “lower” percentages of chemical additive to react with the soil, resulting in improved physical properties.
– Reduced plasticity
– Reduced moisture-holding capacity
– Reduced shrink-swell characteristics
– Improved workability
• Modification relies primarily on short term reactions
– Cation exchange and flocculation/agglomeration
Modification versus Stabilization4/24/2014 21
2. Stabilization
Addition of “higher” percentages of chemical additive to react with the soil, resulting in improved mechanical properties.
– Increased shear strength
– Increased modulus/stiffness
– Increased durability (i.e. resistance to mechanical degradation with repeated loading, wet-dry and freeze thaw cycles)
• Stabilization relies primarily on longer term reactions– Cementation and pozzalanic reactions
Modification versus Stabilization4/24/2014 22
ODOT Definitions (2009 Standard Specifications)Chapter 300 Subgrade Treatment, Section 307.01
A. Subgrade Stabilization
Incorporate chemical additives into the subgrade to increase the strength of the subgrade soils and to provide structural value for the pavement structure.
B. Subgrade Modification
Incorporate chemical additives into the subgrade to change the PI of the subgrade soils and improve its workability as a platform to support construction equipment.
Modification versus Stabilization4/24/2014 23
1. The state of the practice relative to selecting a stabilizer and determining the optimum additive content based on soil properties– Chemical treatment basics– Chemical stabilizers– Modification versus stabilization– Improvements in treated soil behavior– Relevant documents and standards
• ODOT 2009 Standard Specifications, Sections 307 and 700• OHD L-49, OHD L-50, OHD L-51• ASTM D4609, ASTM D6276
4/24/2014 24
• Atterberg limits (LL, PL, PI) (ASTM D 4318, AASHTO T89, T90)
LL
PL
W
(%)
PI
General Comment: Additives decrease LL, increase PL and reduce PI. Amount and rate depends on soil and additive type.
Improvements in Treated Soil Behavior4/24/2014 25
Typical Data for Beto (Brown, CH) Clay
Milburn & Parsons 2004, Parsons & Kneebone 2004
Additive Amount (%)
0 2 4 6 8 10 12 14 16 18
Wate
r C
on
ten
t (%
)
10
20
30
40
50
60
70
Lime
Flyash
CKD
Cement
LL
PL
Additive Amount (%)
0 2 4 6 8 10 12 14 16 18
Wa
ter
Co
nte
nt (%
)
10
20
30
40
50
60
70
PI
Lime
Flyash
CKD
Cement
Improvements in Treated Soil Behavior4/24/2014 26
Typical Data for Hugoton (CL) Clay
Milburn & Parsons 2004, Parsons & Kneebone 2004
Additive Amount (%)
0 2 4 6 8 10 12 14 16 18
Wa
ter
Co
nte
nt
(%)
10
20
30
40
50
Lime
Flyash
CKD
CementLL
PL
Additive Amount (%)
0 2 4 6 8 10 12 14 16 18
Wa
ter
Co
nte
nt (%
)
0
10
20
30
40
50
60
PI
Lime
Flyash
CKD
Cement
Improvements in Treated Soil Behavior4/24/2014 27
• Compaction Properties
– (ASTM D 698, AASHTO T99)
General Comment: Additivesresult in lower gdry-max and higher wopt. Amount of difference depends on soil and additive type, and additive amount.
gd
w
Zero air void lines
Treated
Untreated
Improvements in Treated Soil Behavior4/24/2014 28
Miller et al. 2011
Curing Time (days)
0 5 10 15 20 25 30
UC
S (
psi)
0
50
100
150
200
250
UC
S (
psi)
0
50
100
150
200
250
UC
S (
psi)
0
50
100
150
200
250
UC
S (
psi)
0
50
100
150
200
250
UC
S (
psi)
0
50
100
150
200
250
300
US 281: UCS=56 t0.23
, r2=0.89
Treated
Untreated
Error bars indicate plus and
minus one standard deviation
Penn Ave: UCS=118 t0.18
, r2=0.83
US 177: UCS=112 t0.15
, r2=0.37
SH 7: UCS=131 t0.14
, r2=0.64
US 81: UCS=77 t0.09
, r2=0.76
• Unconfined Compressive Strength (UCS) versus curing time
• UCS=UCS1tRtu
Improvements in Treated Soil Behavior4/24/2014 29
Curing Time (days)
0 5 10 15 20 25 30
UC
S (
psi)
0
50
100
150
200
250
UC
S (
psi)
0
50
100
150
200
250
UC
S (
psi)
0
50
100
150
200
250
UC
S (
psi)
0
50
100
150
200
250
UC
S (
psi)
0
50
100
150
200
250
300
Enid North: UCS=100 t0.35
, r2=0.97
Treated Avg. UCS
Untreated Avg. UCS
Enid South: UCS=20 t0.63
, r2=0.99
US 62: UCS=41 t0.07
, r2=0.71
Perry: UCS=65 t0.17
, r2=0.95
Payne: UCS=59 t0.20
, r2=0.76
Miller et al. 2011, Data from Snethen et al. 2008
• Unconfined Compressive Strength (UCS) versus curing time
• UCS=UCS1tRtu
Improvements in Treated Soil Behavior4/24/2014 30
Curing Time (days)
0 5 10 15 20 25 30
MR (
psi)
0
10000
20000
30000
40000
50000
60000
70000
80000
g d (p
cf)
100
105
110
115
w (
%)
9
10
11
12
13
Individual Test Data
Average of Two Tests
MR=53136 t0.12
, r2=0.81
Untreated
Improvements in Treated Soil Behavior
• Resilient Modulus (MR) versus curing time
• MR=MR1tRt
4/24/2014 31
Miller et al. 2011, and data from Snethen et al. 2008
• A correlation appears to exist between the rate exponents (i.e. Rtu, Rt) and percent of fines for the data from the ten sites mentioned above.
Percent of Fines, F
0 20 40 60 80 100
Rtu
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
CFA
Lime
Lime/CFA
CKD
Rtu=1.27e-0.03F, r
2=0.81
Improvements in Treated Soil Behavior4/24/2014 32
Miller et al. 2011
• A stabilization factor (SF) was developed as an attempt to capture the influence of the fines content, nature of fines, additive content, and additive effectiveness.
• SF = F/100 + LS/20 + AC/20 + UCS1d/120– F=%fines
– LS=untreated linear shrinkage (%)
– AC=additive content (%)
– UCS1d=1-day UCS (psi)
• This parameter was found to provide good correlations to Rtu
and Rt.
Improvements in Treated Soil Behavior4/24/2014 33
Miller et al. 2011, and data from Snethen et al. 2008
0 1 2 3 4
Rtu
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Rtu
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
CFA
Lime
Lime/CFA
CKD
outliers
Rtu=1.25e-0.72SF, r
2=0.91
b)
SF
Rtu=1.26e-0.85SF, r
2=0.53
a)
Improvements in Treated Soil Behavior4/24/2014 34
• A linear relationship (MR=b+m*UCS) was found to provide a good fit of the data in a plot of MR versus UCS for most sites.
• Coefficient of determination, r2, ranged from 0.09 to 0.96 with a median value of 0.74.
• It was found that m and b were correlated reasonably well with percent fines and stabilization factor (SF)
UCS (psi)
0 50 100 150 200 250 300 350
MR (
psi)
0
20000
40000
60000
80000
MR (
psi)
0
100000
200000
300000
400000
500000
600000
700000
US 281: CFA/15.4%
Penn Ave: CFA/13.4%
SH 7: CFA-Lime/12%-4%
SH 177: Lime/2.3%
US 81: CFA/12.2%
Enid North: CKD/14%
Enid South: CKD/12%
US 62: CFA/15%
Perry: CFA/15%
Payne: CFA/16%
MR (
psi)
0
100000
200000
300000
400000
500000
600000
700000
a) all sites
b) previous sites
c) current sites
Miller et al. 2011, and data from Snethen et al. 2008
Improvements in Treated Soil Behavior
4/24/2014 35
Miller et al. 2011, and data from Snethen et al. 2008
Percent of Fines, F
0 20 40 60 80 100
Slo
pe
, m
0
1000
2000
3000
4000
Inte
rce
pt,
b (
psi)
-120000
-100000
-80000
-60000
-40000
-20000
0
20000
40000
60000
80000
CFA
Lime
Lime/CFA
CKD
m=10156e-0.046F, r
2=0.68
a)
b)
b= -94739+1660F, r2=0.51
Improvements in Treated Soil Behavior
MR=b+m*UCS
4/24/2014 36
Miller et al. 2011, and data from Snethen et al. 2008
SF
0 1 2 3 4
Slo
pe
, m
0
1000
2000
3000
4000
Inte
rce
pt,
b (
psi)
-100000
-80000
-60000
-40000
-20000
0
20000
40000
60000
80000
CFA
Lime
Lime/CFA
CKD
m=14201e-1.35SF, r
2=0.70
a)
b)
b= -136208+61526SF, r2=0.76
Improvements in Treated Soil Behavior
MR=b+m*UCS
4/24/2014 37
• Compressibility of Stabilized Soils
– Limited data (e.g. Miller et al. 1996)
– Generally, as strength increases compressibility decreases.
Vertical Stress (kPa)
1 10 100 1000 10000
Ver
tica
l S
trai
n (
%)
-5
0
5
10
15
20
Wetting-Induced Compression Test on
Compacted Shale With and
Without CKD Treatment
ShaleShale with CKD
Water Added
Vertical Stress (kPa)
1 10 100 1000 10000
Ver
tica
l S
trai
n (
%)
-5
0
5
10
15
20
untreated
treated with CKD
Hennessey Shale
Improvements in Treated Soil Behavior4/24/2014 38
• Shrink/Swell of Stabilized Soils– Generally, chemical additives reduce or eliminate shrink/swell
potential.
– As PI increases so does shrink/swell potential
– Typically a “small” amount of additive minimizes shrink/swell potential.
Time (minutes)
0.01 0.1 1 10 100 1000 10000
Fre
e S
wel
l (%
)
0
1
2
3
4
5
Shale
Shale + CKD
Oedometer Free Swell Test on Plastic Shale
Improvements in Treated Soil Behavior4/24/2014 39
1. The state of the practice relative to selecting a stabilizer and determining the optimum additive content based on soil properties– Chemical treatment basics– Chemical stabilizers– Modification versus stabilization– Improvements in treated soil behavior– Relevant documents and standards
• ODOT 2009 Standard Specifications, Sections 307 and 700• OHD L-49, OHD L-50, OHD L-51• ASTM D4609, ASTM D6276
4/24/2014 40
• ODOT 2009 Standard Specifications
– Section 307 Subgrade Treatment
• General construction requirements
• Material requirements found in Section 700
• Application requirements
• Temperature restrictions
• Mixing requirements
• Compaction requirements
4/24/2014 41Relevant Documents and Standards
• ODOT OHD L-49, L-50 and L-51
– OHD L-49 Method of Test for Determining Soluble Sulfate Content in Soil
– OHD L-50 Soil Stabilization Mix Design Procedure
– OHD L-51 Soil Modification Mix Design Procedure
4/24/2014 42Relevant Documents and Standards
• ODOT OHD L-50 Soil Stabilization Mix Design Procedure– Abbreviated procedure: uses basic soil tests and Soil
Stabilization Table– Complete laboratory procedure:
• ASTM D 6276 Standard Test Method for Using pH to Estimate the Soil-Lime Proportion Requirement for Soil Stabilization– Additive content for stabilization is the lowest lime percentage that gives
pH=12.4
• ASTM D 4609 Standard Guide for Evaluating Effectiveness of Admixtures for Soil Stabilization– Test treated samples with different additive contents to determine UCS– Uses Harvard Miniature Samples– Test UCS samples immersed in water for 2 days– Effective stabilization increases UCS by 50 psi or more– Other indicators – PI reduction, swell reduction, etc.
– Other required tests• Soluble sulfate (OHD L-49) for all soils – thresholds 500, 1000,
8000 ppm• Crumb test (ASTM D 6572) for dispersive soil – Divisions 2, 5, 7 or
if dispersive soils suspected
4/24/2014 43Relevant Documents and Standards
• ODOT OHD L-50
4/24/2014 44Relevant Documents and Standards
Soil-additive pH Tests (ASTM D 6276)
Snethen et al. 2008
Additive Amount (%)
0 5 10 15 20 95 100
pH
8
9
10
11
12
13
Lime
Flyash
CKD
Cement
12.5, CKD12.3, Lime, Cement
11.7, Flyash
Lime, 6%
CKD, 8%Cement, 8%
Flyash, 14%
Relevant Documents and Standards4/24/2014 45
Unconfined Compression Test Results
Snethen et al. 2008
UC
S (
psi)
0
20
40
60
80
100
120
140
160
6% Lime
12% Lime
7-Day 28-Day
UC
S (
psi)
0
20
40
60
80
100
120
140
160
6% Flyash
10% Flyash
14% Flyash
7-Day 28-Day
UC
S (
psi)
0
20
40
60
80
100
120
140
160
4% CKD
8% CKD
12% CKD
7-Day 28-Day
Untreated Soil
Relevant Documents and Standards4/24/2014 46
• ODOT OHD L-51
4/24/2014 47Relevant Documents and Standards
2. Adverse reactions and unexpected outcomes from chemical stabilization
– Sulfate bearing soil
– Post-construction wetting
– Laboratory versus field testing
– Other problems
4/24/2014 48
• Sulfate Rich Soils– Soils containing soluble sulfate that reacts with chemical soil additives
containing calcium (i.e. lime, flyash, CKD) resulting in precipitation of calcium sulfate crystals (e.g. Ettringite, Thaumasite).
◦ Major problem is volume increase (and heave) associated with growth of calcium sulfate crystals.
Gypsum
crystals
*
Sulfate Bearing Soils4/24/2014 49
• Adversely Affected by chemical treatment– Sulfate-Rich Soils
Stress (kPa)1 10 100 1000
Ver
tica
l S
trai
n (
%) -6
-4
-2
0
Soil #2
Swelling after
addition of H20Compression
following free
swelling
Oedometer Results for Clayey Soil
Containing 9,000 ppm Sulfate Showing
Moderate Swell Potential
Swell Pressure
Stress (kPa)1 10 100 1000
Ver
tica
l S
trai
n (
%) -6
-4
-2
0
Now with LIME ADDED
Swell Pressure
Soil #2Soil #2 with lime
Change in Free Swell
Sulfate Bearing Soils4/24/2014 50
Sulfate Bearing Soils4/24/2014 51
Sulfate Bearing Soils4/24/2014 52
Sulfate Bearing Soils4/24/2014 53
Sulfate Bearing Soils4/24/2014 54
Sulfate Bearing Soils4/24/2014 55
Sulfate Bearing Soils4/24/2014 56
Sulfate Bearing Soils4/24/2014 57
• Sulfate-Rich Soils – (continued)– Occurrence – Soils/formations containing soluble
sulfate minerals (e.g. gypsum).
– Identification –• Visual inspection and geologic investigation
• Chemical analysis for soluble sulfates (e.g. ODOT OHD L-49, National Lime Association).
– Treatment – Don’t use lime if soil contains appreciable soluble sulfate content (threshold is uncertain – typcially 1,000 to 3,000 ppm). Conduct compatibility tests if in doubt.
Sulfate Bearing Soils4/24/2014 58
2. Adverse reactions and unexpected outcomes from chemical stabilization
– Sulfate bearing soil
– Post-construction wetting
– Laboratory versus field testing
– Other problems
4/24/2014 59
Snethen et al. 2008, Miller et al. 2011
• The DCP and PANDA penetration tests, and the PFWD test showed similar trends at most field test sites and captured the increase in strength and stiffness of stabilized subgrade soils with increasing curing time.
• The test results also reflected a decrease in strength and stiffness at some sites due to significant rain events during curing.
• Field test results also reflected the variability of strength and stiffness at test sites. Thus, the field tests in question show significant promise as tools for monitoring quality and improvement of stabilized subgrades during construction.
Post-Construction Wetting4/24/2014 60
Miller et al. 2011 and Snethen et al. 2008
• Example of Curing with Fair Weather
• Results of Field Testing at Site #5, US 81
Curing Time (days)
0 5 10 15 20 25 30
PF
WD
Evd (
psi)
0
5000
10000
15000
20000
DC
P 1
/DC
I (b
low
s/m
m)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
PA
ND
A q
d (
psi)
0
500
1000
1500
2000
2500
3000
Average
Untreated
Post-Construction Wetting4/24/2014 61
Miller et al. 2011 and Snethen et al. 2008
• Example of Curing with Rainfall Events
• Results of Field Testing at Site #3, US 177
• Approximately 0.6 inches of rainfall between 6 and 15 days.
Curing Time (days)
0 5 10 15 20 25 30
PF
WD
Evd (
psi)
0
5000
10000
15000
20000
DC
P 1
/DC
I (b
low
s/m
m)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
PA
ND
A q
d (
psi)
0
500
1000
1500
2000
2500
3000
Average
Untreated
Post-Construction Wetting4/24/2014 62
2. Adverse reactions and unexpected outcomes from chemical stabilization
– Sulfate bearing soil
– Post-construction wetting
– Laboratory versus field testing
– Other problems
4/24/2014 63
Snethen et al. 2008, Miller et al. 2011
• The UCS and MR values obtained from the laboratory mixed and cured samples were compared to results of DCP, PANDA, and PFWD field tests for ten sites (five previous, five current).
• It was found that there was little or no correlation between the field and laboratory strength and stiffness.
• This was attributed to the significant differences in the curing conditions (i.e. weather) that played a significant role in the results of field tests.
• When data from two sites, that were significantly different, were removed from the data set, a weak correlation was observed between MR and field test results for the remaining eight sites.
Laboratory versus Field Testing4/24/2014 64
Miller et al. 2011 and data from Snethen et al. 2008
1/DCI (blows/mm)
0.0 0.1 0.2 0.3 0.4
UC
S (
psi)
0
50
100
150
200
MR
(psi)
0
20000
40000
60000
80000
100000
120000
140000
160000
a)
b)
US 281
Penn Ave.
SH 7
US 81
US 177
Enid S
US 62
Payne
Mr=28431+161460(1/DCI),
r2=0.22
Laboratory versus Field Testing
• Dynamic Cone Penetration Results versus MR and UCS
4/24/2014 65
Miller et al. 2011 and data from Snethen et al. 2008
qd (psi)
0 1000 2000 3000
UC
S (
psi)
0
50
100
150
200
MR
(psi)
0
20000
40000
60000
80000
100000
120000
140000
160000
a)
b)
US 281
Penn Ave.
SH 7
US 81
US 177
Enid S
US 62
Payne
Mr=23767+16.8qd,
r2=0.23
• PANDA Penetration Test Results versus MR and UCS
Laboratory versus Field Testing
4/24/2014 66
Miller et al. 2011 and data from Snethen et al. 2008
Evd
(psi)
0 5000 10000 15000 20000 25000
UC
S (
psi)
0
50
100
150
200
MR
(psi)
0
20000
40000
60000
80000
100000
120000
140000
160000
a)
b)
US 281
Penn Ave.
SH 7
US 81
US 177
Enid S
US 62
Payne
Mr=10471+4.3Evd,
r2=0.48
Laboratory versus Field Testing
• Portable Falling Weight DeflectometerResults versus MR
and UCS
4/24/2014 67
2. Adverse reactions and unexpected outcomes from chemical stabilization
– Sulfate bearing soil
– Post-construction wetting
– Laboratory versus field testing
– Other problems
4/24/2014 68
• Carbonation
– Reaction of calcium-based products with carbon dioxide in atmosphere producing calcium carbonate.
– Undesirable reaction that retards development of CSHs and CAHs.
Other Problems4/24/2014 69
• Factors that adversely influence soil-chemical reactions:
– Organic carbon content of soil
– Excessive quantities of exchangeable sodium
– Presence of carbonates in soil
If additive performance in doubt, mix design is recommended
Other Problems4/24/2014 70
Bosville + 10% CKD
Compaction Delay (hours)
0 5 10 15 20 25 30 35 40 45 50
UC
S (
kP
a)
200
300
400
500
600
700
800
Average
Sample 1
Sample 2
Sample 3
Other Problems
• Delayed compaction: very important to compact soils containing cementitious additives (Cement, Fly Ash, CKD) in a timely manner after mixing with water
4/24/2014 71
3. Determination of the additive content of compacted soils in the field
– Qualitative methods – pH based
– Quantitative lab methods
– X-ray fluorescence (XRF)
4/24/2014 72
• ODOT 2009 Standard Specifications, 307.04 I
• After completing the final grade, use a color-sensitive indicator solution, such as phenolphthalein or thymol blue, to measure the thickness and uniformity of the compacted soil and chemical mixture in accordance with Subsection 301.04.A(2), “Width and Thickness.” Apply the indicator solution along the side of a small hole excavated to the required depth of chemical treatment and note the depth and uniformity of the color change.
4/24/2014 73Qualitative Methods – pH Based
3. Determination of the additive content of compacted soils in the field
– Qualitative methods – pH based
– Quantitative lab methods
– X-ray fluorescence (XRF)
4/24/2014 74
• ASTM D 3155 – Standard Test Method for Lime Content of Uncured Soil – Lime Mixtures
• Must be uncured specimens – not applicable for forensic investigations
• Titration process, cumbersome, lots of chemicals, operator dependent
• Only for Lime
4/24/2014 75Quantitative Lab Methods
3. Determination of the additive content of compacted soils in the field
– Qualitative methods – pH based
– Quantitative lab methods
– X-ray fluorescence (XRF)
4/24/2014 76
Motivation• We need a versatile and reliable method for measuring
stabilizer content in the field for any additive type and at any time after mixing!
• Construction Quality Control • Can inspect stabilized subgrade and make a determination if enough
stabilizer has been used and have any issues fixed before the pavement is laid.
• Forensic Geotechnical Investigations• Inspectors can collect samples during construction and keep them in
case a roadway performs poorly in the future.
• Samples can be obtained during failure investigations – less accurate than banking samples during construction.
X-Ray Fluorescence (XRF)4/24/2014 77
X-Ray Fluorescence (xrf) Used extensively in environmental applications to measure elemental content in
soils, sediments, water sources, and even foods; however has not been used in soil stabilization applications.
Test measures elemental content as accurately as 0.01 – 100%.
The Whole Rock Analysis Method using XRF was performed by ALS Laboratory Group in Reno, NV.
Used to measure Calcium Oxide (CaO) content of natural soils (CaO0), chemical additives (CaOC.A.), and treated soils (CaOf).
100..0..
0
CaOCaO
CaOCaOCS
AC
f
X-Ray Fluorescence (XRF)4/24/2014 78
How does XRF work?
X-rays are shot from an x-ray tube onto a sample. The x-rays knock individual electrons out of their orbit around an atom. Electrons in the outer orbits then jump down to fill the vacancies. When these electrons “jump”, they emit x-ray fluorescence radiation in amounts specific to the element they are a part of. The XRF radiation is then identified by an XRF detector. The intensity of the radiation is proportional to the concentration of the element in the sample.
X-Ray Fluorescence (XRF)4/24/2014 79
Important Note
• XRF identifies individual elements in samples only. The results of each element are given in parts per million (ppm) or parts per billion (ppb). XRF does not measure compounds. It is standard industry convention to assume that all elements bond with oxygen (O2) to become an oxide. The calculation for this assumption is as follows:
%𝑂𝑥𝑖𝑑𝑒 𝐶𝑜𝑚𝑝𝑜𝑢𝑛𝑑 =𝑒𝑙𝑒𝑚𝑒𝑛𝑡 𝑖𝑛 𝑝𝑝𝑚
10000 ∗ 𝐾
Where K = Conversion Factor that can be found here
X-Ray Fluorescence (XRF)4/24/2014 80
Sample Preparation
• Measure out 9 g of of Lithium Borate Flux then place it in the same platinum crucible. Mix thoroughly.
X-Ray Fluorescence (XRF)4/24/2014 81
Sample Preparation
• Place crucible in Katanax K1 Prime fusion machine then press start.
X-Ray Fluorescence (XRF)4/24/2014 82
Sample Preparation
• Wait 10 minutes and disk will be fused.
X-Ray Fluorescence (XRF)4/24/2014 83
XRF Benchtop Units
• Bruker S2 Ranger
X-Ray Fluorescence (XRF)4/24/2014 84
XRF Portable Units• Olympus X-5000
X-Ray Fluorescence (XRF)4/24/2014 85
Test Soil
Site # Soil NameAASHTO
Group
USCS
Group
Percent
Clay (%)
Liquid
Limit
(%)
Plastic
Limit
(%)
Plasticity
Index
(%)
Shrinkage
Limit (%)
Linear
Shrinkage
(%)
1 and
V1^US 281 A-4 ML 10.3 18 NP* NP 2.2 2.7
2^Penn
Ave.A-6 CL 34.9 40 18 22 14.3 6.2
3 ^US 177 A-7-6 CH 36.5 54 20 34 16.8 7.1
5 ^US 81 A-4 ML 14.0 16 NP NP 1.4 2.6
V2 ^SH7 A-6 CL 22.3 35 14 21 11.7 3.8
V3$Kirkland
PawhuskaA-6 CL 28.6 39 17 22 10 12
V4+Hickory
ClayA-7-6 CH 63.6 71 32 39 19.5 11.5
^ Data from Holderby 2010
$ Data from Hussey 2010 and Tabet 2012
+ Data from Adams 2008 and Campbell 2010
*NP – Non PlasticX-Ray Fluorescence (XRF)4/24/2014 86
Mixed Amount of Stabilizer
0 2 4 6 8 10 12 14 16 18 20
Measure
d S
tabili
zer
Am
ount by X
RF
(%
)
0
2
4
6
8
10
12
14
16
18
20
OHC (White = Lime; Black = CKD; Grey = FA)
Kirkland-Pawhuska
US 281
US SH7
y = .96x+.15; r2 = .99
95% Confidence Band
95% Prediction Band
X-Ray Fluorescence (XRF)4/24/2014 87
Stabilizer Regression r2
Combined y=0.96x+0.15 0.99
Lime y=1x+0.05 0.98
CKD y=0.96x 0.99
Fly Ash y=0.96x+0.16 0.98
Validation Results
X-Ray Fluorescence (XRF)4/24/2014 88
Site #1 Site #2 Site #3 Site #4 Site #5
Class C Fly Ash Quick Lime
X-Ray Fluorescence (XRF)4/24/2014 89
Application to Field Sites
Site
NumberSoil Name
Type of
Stabilizer
Design
Specified
Content (%)
XRF
Determined
Content (%)
Predicted
XRF
Content
from
Validation
Study (%)
#1 US 281 CFA 14 15.415.7-16.3
#2 Penn Ave. CFA 12 13.413.6-14.1
#3 US 177 Quicklime 2.7 2.32.0-2.4
#5 US 81 CFA 14 12.212.4-12.8
X-Ray Fluorescence (XRF)4/24/2014 90
Conclusions
• The “Whole Rock Analysis” Method using XRF technique could be an extremely useful tool to use for quality control applications or during forensic investigations, where the presence or lack of additive in a stabilized layer is in question.
X-Ray Fluorescence (XRF)4/24/2014 91
Conclusions
• Portable field XRF units seem like a promising method to get a fast and accurate measurement, as well as spatial heterogeneity assessment, of the stabilization of a subgrade before the pavement is laid.
• If problem areas are identified, the subgrade can be remixed and compacted in a timely manner.
X-Ray Fluorescence (XRF)4/24/2014 92
XRF Handheld Units
• Olympus Delta Professional • Bruker Tracer III
4/24/2014 93
Recommendations
• For projects involving chemical stabilization, samples of additives, untreated soil, and treated soil (after compaction and final grading) should be obtained at three or more representative locations and representing the full design depth of the stabilized layer.
– The samples are small and can be retained for future testing should disputes arise, or they can be incorporated into the quality control program –recognizing the testing times and limitations involved.
X-Ray Fluorescence (XRF)4/24/2014 94
THANKS!
• QUESTIONS?
• Be sure you have signed in and provided contact information if you want your PDH form mailed to you!
4/24/2014 95