Important Aspects of Chemical Stabilization of Fine ... · PDF fileImportant Aspects of...

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


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.


Dispersed Structure

Add chemical

Add water

Mix

Flocculated/Agglomerated

Structure


• 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.


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


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!


• 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


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


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


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.




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


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


• 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


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


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


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


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.



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)


• 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



4/24/2014 35


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


MR=b+m*UCS

4/24/2014 36


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


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


• 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




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


• 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


• ODOT OHD L-50


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






– 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-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.






– 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


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






– 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


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


4/24/2014 66


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


• Portable Falling Weight DeflectometerResults versus MR

and UCS

4/24/2014 67





– 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





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





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





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


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.


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


http://www.geol.umd.edu/~piccoli/probe/molweight.html

Sample Preparation

• Measure out 9 g of of Lithium Borate Flux then place it in the same platinum crucible. Mix thoroughly.


Sample Preparation

• Place crucible in Katanax K1 Prime fusion machine then press start.


Sample Preparation

• Wait 10 minutes and disk will be fused.


XRF Benchtop Units

• Bruker S2 Ranger


XRF Portable Units• Olympus X-5000


Test Soil

Site # Soil NameAASHTO

Group

USCS

Group

Percent

Clay (%)

Liquid

Limit

(%)

Plastic

Limit

(%)

Plasticity

Index

(%)

Shrinkage

Limit (%)

Linear

Shrinkage

(%)

1 and

V1ÛS 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 ÛS 177 A-7-6 CH 36.5 54 20 34 16.8 7.1

5 ÛS 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


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


Site #1 Site #2 Site #3 Site #4 Site #5

Class C Fly Ash Quick Lime


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


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.


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.


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.


THANKS!

• QUESTIONS?

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