Chat Stabilization Report 2005

CEMENTITIOUS STABILIZATION OF RAW CHAT FOR ROADWAY BASE APPLICATION

______________________________________________________

________________________________________________________________________

Prepared by:

Rajul Teredesai Musharraf Zaman Gerald A. Miller

Robert Nairn School of Civil Engineering and Environmental Science

University of Oklahoma Norman, Oklahoma 73019

Submitted to:

Oklahoma Department of Environmental Quality

Oklahoma City, OK 73101-1677

JULY 13, 2005 (Revised: October 5, 2005)

University of Oklahoma, School of Civil Engineering and Environmental Science

Cementitious Stabilization of Raw Chat for Roadway Base Application

ACKNOWLEDGEMENT

We would first like to express our sincere appreciation to the Oklahoma

Department of Environmental Quality (ODEQ) for providing funding for this project.

Specifically, we would like to thank Dr. Mary Jane Calvey, Tar Creek Supervisor,

ODEQ, and Mr. Dennis Datin and Mr. David Cates, Land Protection Division, ODEQ for

their valuable comments and suggestions during the course of this study.

We would like to express our sincere appreciation to Mr. Naji Khoury, Doctoral

Candidate and Professor Joakim G. Laguros, both from the school of Civil Engineering

and Environmental Science (CEES), University of Oklahoma, for their guidance, advice,

and suggestions throughout the course of this study. Finally, we would like to extend our

thanks to Dr. Thomas Landers, Interim Dean, College of Engineering and Dr. Robert

Knox, Director of CEES for their roles on the Tar Creek projects.



ABSTRACT

This study demonstrated utilization of raw chat from the Kenoyer North Pile in

roadway base applications by stabilizing it with class C fly ash (CFA) or cement kiln dust

(CKD). Raw chat was stabilized with 5%, 10% and 15% CFA or CKD and tested for

unconfined compressive strength (UCS). The results showed a significant gain in strength

(UCS) of raw chat due to stabilization. The UCS of raw chat, stabilized with 10% and

15% CFA was in the range of 500 psi to 700 psi. The corresponding strength of CKD-

stabilized chat was much lower, in the range of 100 psi to 300 psi. Since raw chat does

not have any particles greater than 3/8 inch, it does not satisfy the gradation requirements

for an aggregate base, as specified by the Oklahoma Department of Transportation

(ODOT). Thus, a second batch of tests was performed in which limestone (40%) was

blended with raw chat (60%) and the blend was stabilized with either CFA or CKD. The

UCS of the stabilized chat-limestone blend was higher than stabilized chat without any

limestone. Scanning electron microscopy tests were conducted to examine the reaction

products due to stabilization. Effect of curing time on the strength gain was also

examined. Overall, it was observed that raw chat, can be stabilized with either CFA or

CKD and used as a roadway base. This study was exploratory in nature; a more

systematic study is currently underway as part of the Oklahoma Plan for Tar Creek.

Results of that study will be presented in a future report.



TABLE OF CONTENTS

1.0 Introduction.............................................................................................................................3

1.1 Background .......................................................................................................................... 3 1.2 Scope.................................................................................................................................... 4 1.3 Report Format ...................................................................................................................... 5

2.0 Literature Review ...................................................................................................................6

3.0 Materials and Sources ............................................................................................................8

3.1 Chat ....................................................................................................................................... 8 3.2 Limestone.............................................................................................................................. 9 3.3 Cement Kiln Dust (CKD) ..................................................................................................... 9 3.4 Class C Fly Ash .................................................................................................................. 10

4.0 Experimental Methods ..........................................................................................................14

4.1 Moisture-Density Relationship ........................................................................................... 14 4.2 Sample Preparation............................................................................................................. 14 4.3 Field Testing (Dynamic Cone Penetration Test) ................................................................ 14 4.4 Unconfined Compressive Strength Test ............................................................................. 15 4.5 Scanning Electron Microscopy........................................................................................... 15

5.0 Discussion of Results ..............................................................................................................20

5.1 Dynamic Cone Penetration (DCP) Test.............................................................................. 20 5.3 Unconfined Compressive Strength (UCS) Test.................................................................. 20

6.0 Flexible Pavement Design......................................................................................................29

6.1 Design Parameters............................................................................................................... 29 6.2 Design Procedure ................................................................................................................ 29

7.0 Conclusions and Recommendations .....................................................................................33

7.1 Concluding Remarks........................................................................................................... 33 7.2 Recommendations ............................................................................................................... 34

8.0 References...............................................................................................................................36

Appendix .......................................................................................................................................38



1

LIST OF EQUATIONS

log (CBR) = 2.81 - 1.321 log (DCP) (Equation 5.1)…………………………………(18)

SN = a1D1 + a2D2 (Equation 6.1)…………………………………(29)



2

LIST OF SYMBOLS

CBR – California Bearing Ratio

CFA – Class C Fly Ash

CKD – Cement Kiln Dust

DCP – Dynamic Cone Penetration

ESAL – Equivalent Single Axle Load

ICI – Incremental Cone Index

LOI – Loss On Ignition

SEM – Scanning Electron Microscopy

UCS – Unconfined Compressive Strength

?PSI – Change in the Serviceability Index



3

1.0 INTRODUCTION

1.1 Background

The Tri-State Mining District in northeast Oklahoma, southeast Kansas and southwest

Missouri was the site of substantial zinc and lead ore extraction starting in the late 19th century.

The ore deposits were found at depths between 100 to 400 feet in the Boone Formation, a near-

surface aquifer (Fowler, 1943). Peak production occurred in the early 1920s when the mines

accounted for over 55% of the total zinc production in the country. About 70% of the mill feed

was discarded as coarse chat, while the remaining finer chat was discarded into mine tailings

ponds during the years of active mining (Gray and Stroup, 1943). Approximately 500 million

tons of mine tailings were created during active mining and milling. More than 75% of the mine

tailings have been removed, while about 100 million tons remain (USEPA, 1995). Thus, about

100 million tons of chat is presently stockpiled on the surface of the Tar Creek Superfund Site in

large piles. In its bulk form, chat contains elevated levels of lead, zinc and cadmium which raises

raising potentially serious human health and ecological concerns.

Cementitious stabilization has been widely used in pavement construction. It mainly consists

of mixing stabilizing agents such as fly ash, cement, and kiln dust with aggregates or soil. In the

presence of water, these materials react to form cementitious products that are responsible for the

enhancement of engineering properties pertaining to strength and stiffness. The degree of

enhancement in properties and the mechanisms associated with stabilization can differ from one

stabilizing agent to another (Zaman et al., 1998). For example, cement kiln dust (CKD)

generated during the Portland cement manufacturing process and class C fly ash (CFA) produced



4

in coal- fired thermal power plants exhibit different performances when used in stabilizing

aggregate bases. Several studies have been conducted to investigate the effects of CKD, and/or

CFA on the performance of stabilized soils and aggregates (Laguros and Zenieris, 1987;

Baghdadi et al., 1995; Pandey, 1996; Zhu, 1998; Miller et al., 1999; Hughes, 2002; Khoury and

Zaman, 2002; Khoury et al., 2004).

Limited studies have addressed the influence of such stabilizing agents on the engineering

properties of raw chat. Thus, this study was undertaken to evaluate the performance of raw chat

stabilized with CKD and CFA with the objective of using the product as a base course of a test

road in Miami, Oklahoma. The preliminary results of this exploratory study are presented in this

report. A more systematic laboratory study on chat stabilization is currently underway as part of

the Oklahoma Plan for Tar Creek; results of that study will be presented in a future report.

1.2 Scope

This exploratory study was pursued to examine the potential of using a stabilized chat base

for paving projects in the Tar Creek region. In view of the limited time schedule and budget,

only bench-scale tests were performed to generate data pertaining to pavement design.

This study was divided in two cases: Case I, and Case II. Case I involved the evaluation of

unconfined compressive strength (UCS) of chat stabilized with 5%, 10%, and 15% of either CFA

or CKD. In the second phase, Case II, the UCS of a chat- limestone blend stabilized with 5%,

10%, and 15% of CFA or CKD was evaluated. In both cases, a number of specimens were

prepared at near optimum moisture content and maximum dry density. After compaction,

specimens were cured in a moist room for a specific period, namely 14 and 28 days prior to



5

testing for UCS. It is important to note that in Case II, the addition of limestone aggregate with

raw chat helped satisfy the gradation requirements for a Type A aggregate base, as recommended

by the Oklahoma Department of Transportation (ODOT) specifications (ODOT 1999). No such

gradation requirements were met in the first case (Case I) because the goal was to maximize the

use of raw chat in the stabilized base.

1.3 Report Format

Following the background and scope of this study discussed in Section 1, Section 2 presents

a short literature review. An overview of aggregate sources and their engineering properties is

given in Section 3. Section 4 includes the experimental methods, including moisture-density

tests, sample preparation procedure; UCS tests, and Scanning Electron Microscopy (SEM)

techniques. A discussion of the results of the dynamic cone penetration (DCP) tests, unconfined

compressive strength (UCS) tests and SEM micrographs are presented in Section 5. Section 6

includes the design of a typical flexible pavement based on the data obtained from this study,

followed by the conclusions and recommendations for further studies in Section 7.



6

2.0 LITERATURE REVIEW

Cementitious stabilization is widely used to transform a weak or unstable road base into a

structurally sound foundation. Previous studies (Laguros and Zenieris, 1987; Baghdadi et al.,

1995; Pandey, 1996; Zhu, 1998; Miller et al., 1999; Khoury and Zaman, 2002; Khoury et. al.,

2004) have shown that cementitious stabilization can significantly improve the engineering

properties such as strength and modulus of an aggregate base. It also has been found to improve

resistance to fracture, fatigue, permanent deformation and the damaging effects of moisture. For

example, Laguros and Zenieris (1987) and MRS (1989) examined the strength characteristics of

five different types of aggregate bases stabilized with fly ash. The UCS of specimens with 35%

fly ash increased from 308 psi (for 28-day cured samples) to 955 psi (for 90-day cured samples).

In a related study, Pandey (1996) reported that unconfined compressive strengths (UCS) of

the aggregate specimens cured for 7 days were approximately three to seven times higher than

those of the raw aggregate specimens; modulus of elasticity values also exhibited increases due

to stabilization. In a recent study, Khoury (2001) reported that a significant increase in resilient

modulus (Mr) can be achieved with CFA stabilization. According to Khoury (2001) ten percent

CFA could be considered the optimum amount of stabilizing agent for a limestone aggregate in

Oklahoma.

According to Zhu (1998), stabilization of aggregates with 15% CKD can yield an increase in

resilient modulus of 120%, over that of raw aggregate. CKD stabilization, however, has little

effect on the flexural strength. As per Zhu (1998), crystals formed during the hydration process

of CKD stabilization contribute to the formation of cementing particles as an integral body,



7

while filling up the intracluster voids of fine particles and minimizing possible elastic

deformation of the aggregate. Also according to Zhu (1998), the layer coefficient, an important

pavement design parameter, the 28-day cured aggregate samples stabilized with 15% CKD was

found to be at least two times higher than the layer coefficient of raw aggregate samples.

Hughes (2002) conducted a laboratory study to evaluate the feasibility of integrating chat and

fly ash into a roadway subgrade. A number of laboratory tests were performed on stabilized

specimens. Among these tests was the UCS test. Aggregates passing the US Std. No. 4 sieve

were used to determine the moisture-density relationship and to prepare Harvard Miniature

specimens developed by Wilson (1950). The apparatus consists of a small cylindrical mold and a

tamper employing a spring- loaded plunger. Results showed that the UCS increased with the

percentages of fly ash. At 14% CFA, the UCS value was approximately 28 psi compared to

approximately 8 psi for raw specimens. It was also found that soaked specimens had lower UCS

values compared to specimens without soaking.

Another study by Khoury et al. (2004) showed that CFA stabilization enhances the flexural

properties of a stabilized aggregate base. It was reported that the flexural strength values of 10%

CFA stabilized specimens cured for 1 hour, 3 days, and 28 days were higher compared to

unbound raw specimens; raw specimens failed under their self weight, and the flexural strength

was considered negligible for these specimens.



8

3.0 MATERIALS AND SOURCES

3.1 Chat

Raw chat from the Kenoyer North Pile, located north of Miami, Ottawa County, Oklahoma

was used in this study. Figure 3.1 shows a photographic view of the Kenoyer raw chat pile. The

physical properties are summarized in Table 3.1. The L.A. abrasion value is approximately 18%.

According to Oklahoma Department of Transportation (ODOT), an aggregate base with an L.A.

abrasion value less than 40 is considered a good aggregate and can be used in a pavement

applications. In addition, the aggregate durability of chat is approximately 78% compared to the

minimum value of 40% recommended by ODOT.

The gradation of the raw chat used in this project is shown in Figure 3.2, along with the

gradation curves for a Type A aggregate base in accordance with the ODOT specifications. The

maximum aggregate size of chat from this source is approximately 3/8 inch. The maximum

aggregate size according to ODOT specifications is 1.5 inches. Thus, raw chat does not meet the

gradation requirements for a Type A aggregate base on the coarse end. Also, the chat does not

have a sufficient percentage of particles passing the US No. 200 sieve to satisfy the ODOT

requirements for a type A aggregate base.

The mineralogical properties are summarized in Table 3.2. From Table 3.2, one can

conclude that chat (retained on the US No. 50 sieve) contains about 73% silica, 11% dolomite,

17% calcium carbonate (CaCO3), and 1% hemimorphite. On the other hand, chat passing the US

No. 200 sieve has a lower amount of SiO2 (approximately 65%) and CaCO3 (7%), and a higher

amount of dolomite (18%), and hemimorphite (10%).



9

3.2 Limestone

Limestone is one of the most abundantly available sedimentary rocks for road construction in

Oklahoma. It is primarily composed of calcium carbonate or a combination of calcium and

magnesium carbonates with varying amounts of impurities, the most common of which are silica

and alumina (Boynton, 1980). Vinita, a limestone-type aggregate, was used in this study to

modify the gradation of raw chat so that the final blend met the ODOT requirement for a Type A

aggregate base gradation. Bulk samples were collected from the Vinita Rock Company, near

Vinita, Oklahoma. A summary of the most important aggregate properties is presented in Table

3.3. The L.A. abrasion value for limestone is 23% , which is higher than that of chat. The

aggregate durability, on the other hand, is slightly lower (71%) than that of raw chat (78%).

Additional physical properties for the Vinita aggregate are presented in Wasiuddin et al. (2005).

3.3 Cement Kiln Dust (CKD)

CKD produced by Lafarge Corporation, Tulsa, Oklahoma was used in this study. CKD is a

by-product material generated while manufacturing Portland cement. The silica, alumina, and

ferric oxide, (SAF) amount is approximately 20%. The total calcium oxide for this CKD is 48%,

of which approximately 7% is in free form. The loss on ignition (LOI) value is 26. These

properties were provided by the manufacturer. Additional chemical and physical properties are

presented in Table 3.4.



10

3.4 Class C Fly Ash

CFA was also provided by Lafarge Corporation, Tulsa, Oklahoma. CFA is produced from

the combustion of coal in an electric utility plant. CFA used in this study has an SAF content of

approximately 65% and a calcium oxide (lime, CaO) content of approximately 24%; the free

amount of lime in CFA was not provided and no attempts were made to determine the free lime

amount. Loss of ignition (LOI) is approximately 0.16. Table 3.4 presents a summary of

additional physical and chemical properties.



11

Figure 3.1 Photographic View of the Kenoyer Chat Pile Near, Miami, Oklahoma

0102030405060708090

100

0.01 0.1 1 10 100

Sieve Size in mm

% P

assi

ng

Type A Lower Type A Upper Raw Chat

Figure 3.2 Gradation of Raw Chat and Type A Aggregate Base



12

Table 3.1 Physical Properties of Chat (Wasiuddin et al., 2005)

TESTS VALUE REQUIREMENT Coarse Aggregate Angularity 100% Min. 95% for Surface and

Min. 80% for Base Fine Aggregate Angularity 46% Min. 45% for Surface and

Min. 40% for Base Flat or Elongated Particles <5% Max. 10%

Sand Equivalent 86% Min. 45% L.A. Abrasion 18% Max. 40%

Aggregate Durability Index 78% Min. 40% Insoluble Residue 98.33% Min. 40%

Table 3.2 Mineralogical Properties of Chat (Wasiuddin et al., 2005)

COMPOUNDS Retained on No. 50 Sieve Passing No. 200 Sieve % Quartz (SiO 2) 73 65

% Dolomite [CaMg(CO3)2]

11 18

% Calcite (CaCO3)

15 7

% Hemimorphite Zn4Si2O7(OH)2.H2O 1 10

Table 3.3 Chat and Limestone Properties (Wasiuddin et al. 2005)

PROPERTIES Limestone Chat L.A. abrasion value 23 18 Aggregate durability 71 78 Insoluble residue (%) 25 25



13

Table 3.4 Chemical and Physical Properties of CKD and CFA

Chemical Composition (%) CKD CFA SiO2 14.66 36.55 Al2O3 3.34 21.45 Fe2O3 1.38 6.19 CaO 47.98 24.23 MgO 1.83 5.37 SO3 2.78 1.17

Na2O 0.22 1.42 K2O 1.26 --

Na2O eq 1.04 -- LOI 26.03 0.16

Free Lime 7.60 -



14

4.0 EXPERIMENTAL METHODS

4.1 Moisture-Density Relationship

The optimum moisture content (OMC) and maximum dry density (MDD) of raw chat and

chat-limestone blend (with or without stabilizing agent) were determined in accordance with the

ASTM D 1557 test method. A mechanical rammer was used for compaction. A summary of the

OMC and MDD values is presented in Table 4.1. Results from Table 4.1 were used to prepare

the specimens for unconfined compressive strength test at near OMC and MDD. An increase in

both dry density and OMC, have been noticed compared to the corresponding value of the raw

chat, except for 15% CFA. The OMC for 15% CFA decreased approximately 0.5% compared to

the corresponding OMC of raw chat.

4.2 Sample Preparation

A total of 36 specimens were molded at near OMC and MDD. The test matrix for this study

is given in Tables 4.2 and 4.3. Specimens were prepared in accordance with a laboratory method

recommended by Chen (1994) and modified by Khoury (2001). Specimens were molded in a

cylindrical (6 in x 12 in) mold. After compaction, specimens were cured in a moist chamber

having a controlled temperature of 70oF and a relative humidity of 95% (± 2.5%). It is important

to note that stabilized raw chat specimens were cured for 14 and 28 days, while the stabilized

chat–limestone specimens were only cured for 28 days.

4.3 Field Testing (Dynamic Cone Penetration Test)

Dynamic cone penetration (DCP) tests were performed at the proposed test road site shown



15

in Figure 4.1 to estimate California Bearing Ratio (CBR) of the existing subgrade soil. The DCP

test was performed at 12 selected locations, at approximately 1000 foot intervals along the length

of the test road. The CBR values obtained from the DCP tests were used in pavement design

discussed in Section 6. Test borings were done at eight selected locations where DCP tests were

conducted to analyze the existing soil strata. Subgrade soils from these borings were collected

for determination of moisture content, moisture-density relationship and index properties. Figure

4.2 shows a photographic view of the dynamic cone penetration test. The DCP data from this

field testing are summarized in graphical form in the Appendix. A discussion of these results is

included in Section 5.

4.4 Unconfined Compressive Strength Test

The UCS tests were performed in accordance with the ASTM D 5102 test method. Tests

were performed on specimens stabilized with different percentages of CKD or CFA and cured

for specific periods of time, as shown in Table 4.2 and 4.3. Attempts were made to perform the

UCS test on raw chat specimens molded at near OMC and MDD. However, due to lackof

cohesion, these specimens failed under their self weights and the UCS values were considered

negligible.

4.5 Scanning Electron Microscopy

Scanning electron microscopy (SEM) tests were employed in this study to visually observe

the microstructural development in the matrix of chat-CFA or chat-CKD mix, with or without

limestone. The SEM results were useful in identifying the reaction products in the mix due to

different additive types (CFA or CKD). Broken samples from UCS were used to collect a small



16

but representative amount of material for SEM testing. The collected materials were mounted on

the copper stub (sample holder) with the help of carbon paint. The specimens were then coated

with a thin layer of gold palladium to provide surface conductivity. A Tecnic’s sputter coater

operating under 40 millitor vacuum and 5 milliampere current was used for this purpose. Argon

was used as the ionizing gas. The coated specimens were then placed in a JEOL JSM 880

Scanning Electron Microscope operating at 15 kV. Digital images, called micrographs, were

taken and used to identify the reaction products.



17

Table 4.1 A Summary for Optimum Moisture Content and Maximum Dry Density

MATERIALS OMC (%) MDD (pcf) Raw Chat

Raw Chat 6.0 128 Chat with CKD

Raw Chat + 5% CKD 7.2 133 Raw Chat + 10% CKD 7.7 137 Raw Chat + 15% CKD 8.1 136

Chat with CFA Raw Chat + 5% CFA 6.2 136 Raw Chat + 10% CFA 6.6 138 Raw Chat + 15% CFA 5.5 137

Chat-Limestone Raw Chat + Limestone 5.7 129

Table 4.2 Test Matrix for Raw Chat Stabilized with CFA and CKD

Additive

Type

% Chat

% Additive

by weight

Curing period (days)

No. of Samples

14 2 95 5 28 2 14 2

90 10 28 2 14 2

CFA

85 15 28 2 14 2 95 5 28 2 14 2

90 10 28 2 14 2

CKD

85 15 28 2



18

Table 4.3 Test Matrix for Chat-Limestone Blend Stabilized CKD and CFA

Additive Type % Chat

% Additive

by weight

Curing period (days)

No. of Samples

60 5 2 55 10 2 CFA

40 15 2 60 5 2 55 10 2 CKD

40 15

28

2



19

Figure 4.1 Location of The Test Road Site Near Miami, Oklahoma

DCP Test in Progress

Proposed Test Road Section

Figure 4.2 Dynamic Cone Penetration Test at The Test Road Site

Road E030 Test Road



20

5.0 DISCUSSION OF RESULTS

5.1 Dynamic Cone Penetration (DCP) Test

Limited field testing was done at the test road site on May 23, 2004, which included DCP

testing at twelve selected locations. Also, eight boring logs were performed for soil classification

purposes. The locations of the eight boring logs are listed in Table 5.1. A description of soil

types from the boring logs is presented in Table 5.2. The incremental cone index (ICI) is the

amount of penetration in mm per blow and is usually plotted along the depth. The ICI results are

summarized graphically in Appendix I. It should be noted that a higher value of ICI indicates a

softer soil stratum. The ICI values were used to calculate the California Bearing Ratio (CBR)

using the relationship

log (CBR) = 2.81 - 1.321 log (DCP)………….Equation 5. 1

as suggested by the ODOT specifications. The CBR is plotted as a percentage versus depth in

Appendix I. The average CBR was found to be 21%. The subgrade stability is generally related

to the CBR value. This CBR value and the results of the UCS tests were used to estimate

parameters required for the pavement design as described in Section 6.

5.3 Unconfined Compressive Strength (UCS) Test

The UCS values for chat stabilized with CFA are graphically illustrated in Figure 5.1.

Overall, the UCS increased as the percentages of CFA increased from 5% to 15%. The degree of

increase varied with the amount of CFA. For example, the average UCS value for 15% CFA

specimens is significantly (four to seven times) higher than the specimens with 5% CFA and



21

cured for 28 days. This observation is consistent with previous studies (Zaman et al., 1998). In

Zaman et al. (1998), however, the magnitude of increase was much lower and the aggregate type

was different. From Figure 5.1, one can also see that 28-day cured specimens have higher

strengths than 14-day cured specimens. For instance, specimens stabilized with 15% CFA and

cured for 28 days have an average UCS value of 758 psi compared to 296 psi for specimens

cured for 14 days. This observation is also consistent with the results reported by Zaman et al.

(1999) for different type of aggregates.

Figure 5.2 shows the variation of UCS values with the percentage of CKD. The UCS

increased approximately 500% as the percentage of CKD increased from 5% to 15%, for

specimens cured for 28 days. The effect of curing time on CKD specimens is also presented in

Figure 5.2. The UCS values increased with curing time, as expected. For example, the UCS

values for 15%-CKD specimens cured for 28 days is approximately 284 psi compared to 171 psi

for specimens cured for 14 days.

From Figures 5.1 and 5.2 one can conclude that although both the CKD and CFA stabilized

specimens exhibited the same trends; the CFA-stabilized specimens have higher strengths. From

the SEM micrographs, it is believed that more cementitious products were formed in the CFA-

stabilized specimens than the CKD-stabilized specimens. Since raw chat specimens without any

stabilizing agents could not be tested because of lack of cohesion and sample integrity, no UCS

results are available for raw chat.

The results of the UCS tests on chat- limestone specimens, in the presence of stabilizing

agents (CFA or CKD), are graphically illustrated in Figure 5.3. The UCS values exhibited an

increase with the increase in CFA percentage. The average UCS values are approximately 150



22

psi, 275 psi, and 760 psi, for 5% CFA, 10% CFA, and 15% CFA specimens, respectively. As for

CKD specimens, an increase in UCS values was observed when the CKD amount was increased

from 5 % to 10%, beyond which a reduction occurred. No attempts were made to mold

additional specimens to justify such behavior.

5.4 Scanning Electron Microscopy

SEM tests were performed to evaluate the changes in microstructure and to visually examine

the hydration products due to CFA and CKD stabilization. Tests were performed on selective

specimens. Figure 5.4 shows a micrograph of raw chat. These materials do not have any definite

shape but they are generally very angular. The effect of 5% and 15% CKD on the micro-

structural development is illustrated in Figures 5.5 and 5.6. Figures 5.5 and 5.6 show the crystal

formation around the chat and limestone particles as a result of the hydration of CKD. Images of

samples containing chat, limestone and CFA are presented in Figures 5.7 and 5.8. These figures

show the cementing mastic formation in the mix having 5% and 15% CFA. Partially reacted fly

ash can be seen in each figure. The figures show the spherical shape of the fly ash particles.

Needle like crystal structures are also shown in these figures. The crystals create an intricate

structure which binds and envelops the chat particles and partially reacted fly ash particles,

resulting in strength development.

The SEM confirms hydration of CFA and CKD in the chat matrix, which help explain the

results obtained from the UCS test and reinforce the assumption that increase in strength was the

result of hydration of CKD and CFA.



23

Table 5.1 Locations of DCP Tests and Boring Logs at The Test Road Site

Location DCP Borings Chainage(ft) 1 1 B1 150

2 B2 1150 2

3 - 1150 3 4 B3 2150 4 5 B4 3150 5 6 B5 4150 6 7 B6 5150 7 8 - 6150 8 9 B7 7150 9 10 - 8150 10 11 B8 9150 11 12 - 10140

Note: All the distances were measured from the west end of the road.



24

Table 5.2 Description of Soil Profiles from Boring Logs

Soil Profiles in Depth (in)

B1 B2 B3 B4 B5 B6 B7 B8 0 1 2 3

Silty coarse gravel

4

Silty fine to coarse sand (moist),chat (SM)

"Chat" silty sand, traces of fine gravel, damp, brown

5 6

Silty sand

7

Grey Brown moist silty clay (CL)

8

Brown and silty clay (CL) damp

Brown clayey silt

Brown grey clayey silt, damp (CL-ML)

Brown grey clayey silt, damp (CL-ML)

9 10 11

12

Reddish brown mottles of clay (CH) moist and plastic

Brown to brown grey sandy silt (SM), traces of clay " weathered chat"

13 14

Dark Brown clayey silt

15

Grey Clayey Silt (CL-ML)

16

Brown mottles (CH) moist and plastic

Reddish Brown Clay

17

Grey brown mottle of clay , moist

18 19 20 21 22 23 24

Brown mottle of clay (CH) moist and plastic

Moist Fat Clay

Grey Clayey Silt (more clayey)(CL-ML)

Red- brown mottled clay (CH fat clay) damp

Orange- brown mottled clay (CH fat clay) damp

Grey brown fat clay, damp to moist

Brown silty clay (CL), moist, more clayey at 19" , mottled red at 23"

light brown clayey silt, traces of gravel

Chainage (ft) 150 1150 2150 3150 4150 5150 7150 9150 Notes: • Distance is measured from the west end of the test road • The soil classification was performed in accordance with Unified Classification System

explained by ASTM D2487. • CL- Low plasticity clay CH- High plasticity clay ML-Low plasticity silt SM- Silty Sand



25

0

100

200

300

400

500

600

700

800

0 5 10 15 20

% CFA

UC

S, p

si

14 days 28 days

Figure 5.1 Variation of UCS Values with Time and Percentages of CFA

0

50

100

150

200

250

300

0 5 10 15 20

% CKD

UC

S, p

si

14 days 28 days

Figure 5.2 Variation of UCS Values with Time and Percentages of CKD



26

0

100

200

300

400

500

600

700

800

0 5 10 15 20

Percentage

UC

S, p

si

CFA CKD

Figure 5.3 Variation of UCS of Chat-Limestone Blend with CFA and CKD Percentages

3000x Magnification 10000x Magnification

Figure 5.4 Chat Pan at 3,000x Magnification and 10,000x Magnification



27


Figure 5.5 Chat-Limestone Matrix stabilized with 5% CKD


Figure 5.6 Chat-Limestone Matrix Stabilized with 15% CKD



28


Figure 5.7 Chat-Limestone Matrix Stabilized with 5% CFA


Figure 5.8 Chat-Limestone Matrix Stabilized with 15% CFA



29

6.0 FLEXIBLE PAVEMENT DESIGN

The data obtained from the UCS and DCP tests were used to design a flexible

pavement. The AASHTO method of pavement design was used. The design steps are

given by Huang (1993).

6.1 Design Parameters

The proposed test road is a county road. On the basis of existing traffic on the road

and estimated growth in traffic in coming years, the equivalent single axle load (ESAL)

value was assumed as 0.3 million. This is probably a highly conservative estimate,

meaning that the actual ESAL value will probably be much lower. ESAL is a means of

equating various axle loads and configurations to the damage done by a number of

18,000 pound single axles with dual tires on pavements of specified strength over the

design life of the pavement. As recommended by Huang (1993), the “Reliability” was

considered to be 95% and the “Standard Deviation” was assumed as 0.35. Change in the

“Serviceability Index” (?PSI) was assumed to be 2.5. From the DCP test data, the

average value of the CBR was estimated to be 21 using Equation 5.1.

6.2 Design Procedure

Figure 6.1 (Huang 1993) shows a nomograph, also called a design chart, for flexible

pavements, based on the mean value of each input. Using the aforementioned design

input parameters for reliability and overall standard deviation in Figure 6.1, the design

structural number (SN) for the proposed pavement was estimated. Figure 6.2 shows a

correlation chart for estimating the resilient modulus of subbases. For a CBR value of 21,

the modulus of the existing subgrade was estimated to be 13,000 psi. The combined SN



30

was estimated to be 2.4, using Figure 6.1. The modulus of elasticity for asphalt was

assumed to be 350,000 psi, which is a reasonable value in the absence of actual

laboratory/field data. Using the graphical relationship in Figure 6.3, for a modulus value

of 350,000 psi for hot mix asphalt (HMA), the structural coefficient a1 was estimated to

be 0.4. The nomograph in Figure 6.4 for a cement treated base was used for CFA/CKD

stabilized chat because there is no nomograph available for CFA/CKD stabilized bases.

The layer coefficient for the stabilized base was determined to be 0.14. The (SN) of the

overall pavement was established from the following equation:

SN = a1D1 + a2D2………..Equation 6. 1

where D1 and D2 are thicknesses of surface course and base course, respectively, and a1

and a2 are the corresponding layer coefficients. Using a 4- in thick surface course (chat-

asphalt) and a 6- in thick base course (stabilized chat), and the layer coefficients

mentioned above, the SN of the overall pavement was found to be 2.44. This number is

adequate in view of 2.4 which is for a pavement with an estimated ESAL value of 0.3

million.



31

Figure 6.1 Design Chart for Flexible Pavements Based on Mean Values of Each Input (Huang, 1993)

Figure 6.2 Correlation Chart for Estimating Resilient Modulus of Sub-bases

(Huang, 1993)



32

Figure 6.3 Chart for Estimating Layer Coefficient of Dense-graded Asphalt Concrete Based on Elastic Modulus (Huang, 1993)

Figure 6.4 Correlation Chart for Estimating Resilient Modulus of Cement Treated

Base Courses (Huang, 1993)



33

7.0 CONCLUSIONS AND RECOMMENDATIONS

7.1 Concluding Remarks

This study was undertaken to evaluate the performance of chat stabilized with fly ash

and cement kiln dust. Specimens were prepared by compaction at near optimum moisture

content and maximum dry density. The moisture-density relationship for raw, and

stabilized chat was established in accordance with the ASTM 1557 test method. After

compaction specimens were cured for 14 and 28 days in a moist room having a controlled

temperature of 71oF and a relative humidity of approximately 95%. The unconfined

compressive strength of cylindrical specimens prepared using pile-run chat mixed with

three different percentages (5%, 10%, and 15%) of additives (CFA or CKD) was

determined. Tests were performed in accordance with the ASTM D 5102 test method.

Additional specimens were prepared with chat- limestone blend to meet the gradation

requirements for a roadway base, as recommended by ODOT.

Results from this study showed that the UCS depends on the stabilizing agent,

amount of stabilizing agents, and curing time. The UCS values of CFA specimens

exhibited higher values than the corresponding values of CKD specimens. This is an

indication that more cementitious products were formed in CFA specimens compared to

CKD specimens. Raw chat specimens failed under self weight so no UCS tests could be

conducted.

The effect of curing time on the UCS of stabilized chat was observed on both CKD

and CFA-stabilized specimens. Results showed that the UCS values increased with

curing time.



34

The chat- limestone blend stabilized with CFA exhibited an increase in strength as the

percentages of CFA increased up to 15%. As for CKD, the strength increased with the

increase in CKD amount up to 10%, beyond which a reduction is observed; no attempts

were made to mold up additional specimens to justify such behavior. Also, no efforts

were made to observe the effect of curing time on specimens prepared from chat-

limestone blend stabilized with CFA or CKD.

SEM was used on selective specimens to visually observe the micro-structure

development of cementitious compounds with time and stabilizing agents. The

micrographs showed the presence of crystal formation for chat- limestone specimens

stabilized with with CKD or CFA. The formation of hydration coating and crystal

formation in the specimens is believed to be responsible for the strength gain.

7.2 Recommendations

The preliminary results of this exploratory study are presented in this report. A

more systematic laboratory study on chat stabilization is currently underway as part of

the Oklahoma Plan for Tar Creek; results of that study will be presented in a future

report.

Based on findings from the present study, it is recommended that additional

laboratory tests be performed to determine the resilient modulus of stabilized chat, since,

resilient modulus is a critical parameter for pavement design and better simulates the

field conditions. Permeability of stabilized aggregate base that controls the drainage

should also be addressed in future studies.

It is also recommended that analytical techniques such as X-ray diffraction (XRD),

electron dispersive energy (EDS), among others, be used to identify the cementitious



35

compounds in stabilized chat. Field testing, namely, falling weight deflectometer (FWD),

impulse response (IR), and spectral analysis of surface waves (SASW) to identify the

engineering properties for different layers will help examine the performance of the

pavement with stabilized chat base. Correlation between the laboratory and field results

would be beneficial to establish specifications for designing a pavement with stabilized

chat base.



36

8.0 REFERENCES

Baghdadi, Z.A., Fatani, M.N., Sabban, N.A., Soil Modification by Cement Kiln Dust, Journal of Materials in Civil Engineering, Vol. 7, No. 4, November 1995, pp. 218-222.

Boynton, R.S. (1980), Chemistry and Technology of Lime and Limestone, 2nd Edition,

Wiley-Interscience Publication, New York. Chen, D.H. (1994), Resilient Modulus of Aggregate Bases and a Mechanistic-Empirical

Methodology for Flexible Pavement, Ph.D. Dissertation, University of Oklahoma, Norman, Oklahoma.

Fowler, G.M. (1943), Tri-State Geology, Engineering and Mining Journal, Vol. 144, No.

11, pp. 73-79 Prairieville, Los Angeles., California. Gray, H.A. and Stroup, R.J. (1943), Transportation, Engineering and Mining Journal,

Vol. 144. Huang, Y. (1993), Pavement Analysis and Design, Prentice Hall, Inc., Englewood Cliffs,

N.J. Hughes, M. (2002), Sub-grade Stabilization Using Unwashed Mine Tailings From The

Tar Creek Superfund Site, A Report Submitted to Oklahoma Department of Transportation.

Khoury N. (2001), The effect of Freez-Thaw And Wet-Dry Cycles on Resilient Modulus

of Class C Fly Ash Stabilized Aggregate Base, M.S. Thesis, University of Oklahoma, Norman, Oklahoma.

Khoury, N. N. and Zaman, M. M. (2002), Effect of Wet-Dry Cycles on Class C Fly Ash

Aggregate Base, Transportation Research Record, Journal of the Transportation Research Board, Geomaterials, No. 1787, pp.13-21, Washington D.C., 2002.

Khoury, N.N., Srour, C, and Zaman, M. (2004), Performance of Stabilized Aggregate

Base Under Flexural and Compressive Cyclic Load, accepted for publication in the Geo-Trans 2004 Conference proceedings, July 27-31, 2004, UCLA campus, Los Angeles, CA, USA.

Laguros, J.G. and Zenieris, P. (1987), Feasibility of Using Fly Ash as a Binder in Coarse

and Fine Aggregates for Bases, Report No. ORA 155-404, University of Oklahoma, Norman, Oklahoma.



37

Miller, A. G., M.M. Zaman, J. Rahman, and K.N. Tan, Laboratory and Field Evaluation of Soil Stabilization using Cement Kiln Dust, Draft Report, Item 2144, ORA 125-5693, submitted to Oklahoma Department of Transportation (ODOT), Feb. 1999.

Materials Research Society (1989), Fly Ash and Coal Conversion By-Products:

Characterization, Utilization and Disposal V, Vol. 136, pp. 185. Oklahoma Department of Transportation (1999), Standard Specifications for Highway

Construction, Section 703.02. Pandey, K.K. (1996), Evaluation of Resilient Modului and Layer Coefficients of a Coal

Ash Stabilized Marginal Aggregate Base for AASHTO Flexible Pavement Design, Ph.D. Dissertation, School of Civil Engineering and Environmental Science, University of Oklahoma, Norman, Oklahoma.

US Environmental Protection Agency (EPA) (1995), Fact Sheet on Mine Waste, EPA

Region 7, Texas.

Wasiuddin, N., Zaman, M., Nairn R. (2005), A Laboratory Study to Optimize the Use of Raw Chat in Hot Mix Asphalt for Pavement Application, A Report Prepared for Oklahoma Department of Environment Quality, Oklahoma City, Oklahoma.

Wilson, S.D. (1950), Small Soil Compaction Apparatus Duplicates Field Results Closely,

Engineering New-Record, Vol. 145, No. 18, p.p. 34-36. Zaman M., Laguros J., Tian P., Zhu J., Pandey K., (1998), Resilient Moduli of Raw and

Stabilized Aggregate Bases and evaluations of Layer Coefficients for AASHTO Flexible Pavement Design, Final report, Submitted to ODOT, Item 2199, ORA 125-4262, August 1998.

Zhu J. (1998), Charecterization of Cement Kiln Dust Stabilized Base/Subbase Aggregate,

Ph.D. Dissertation, School of Civil Engineering and Environmental Science University of Oklahoma, Norman, Oklahoma.



38

APPENDIX

Graphical Summary of Dynamic Cone Penetration Test (DCP)



39

Fig. 10.1 Summary of Dynamic Cone Penetration (DCP) data

DCP 1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 100

Incremental Cone Index (mm/bow)

Dep

th (

m)

DCP 2

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20


Dep

th (

m)

DCP 3

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100


Dep

th (m

)

DCP 4

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100


Dep

th (m

)

DCP 5

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50


Dep

th (m

)

DCP 6

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 20 40


Dep

th (m

)

DCP 7

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 100


Dep

th (m

)

DCP 8

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100


Dep

th (m

)

DCP 9

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50


Dep

th (

m)

DCP 10

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50


Dep

th (m

)

DCP 11

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50


Dep

th (

m)

DCP 12

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100


Dep

th (m

)



40

Fig 10.2 Summary of CBR from DCP test using the relation

CBR 7

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 100

CBR (%)

Dep

th (

m)

CBR 1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-10 40

CBR %

Dep

th (

m)

CBR 2

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 500

CBR %

Dep

th (

m)

CBR 3

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 100

CBR %

Dep

th (

m)

CBR 4

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50

CBR %

Dep

th (

m)

CBR 5

0

0.1

0.2

0.3

0.4

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0.8

0.9

1

0 100

CBR %

Dep

th (

m)

CBR 6

0

0.1

0.2

0.3

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0.6

0.7

0.8

0.9

1

0 100

CBR %

Dep

th (

m)

CBR 8

0

0.1

0.2

0.3

0.4

0.5

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0.9

1

0 100

CBR (%)

Dep

th (

m)

CBR 9

0

0.1

0.2

0.3

0.4

0.5

0.6

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1

0 50

CBR (%)

Dep

th (

m)

CBR 10

0

0.1

0.2

0.3

0.4

0.5

0.6

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0.8

0.9

1

0 100

CBR (%)

Dep

th (

m)

CBR 11

0

0.2

0.4

0.6

0.8

1

1.2

0 100

CBR (%)

Dep

th (

m)

CBR 12

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 100

CBR (%)

Dep

th (

m)

Chat Stabilization Report 2005

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