TEST FRAMEWORK DEVELOPMENT FOR USE OF COAL COMBUSTION PRODUCTS (CCPS) IN EMBANKMENT CONSTRUCTION AND MINE LAND RECLAMATION

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TEST FRAMEWORK DEVELOPMENT FOR USE OF COAL COMBUSTION PRODUCTS (CCPS) IN EMBANKMENT CONSTRUCTION AND MINE LAND RECLAMATION

ABSTRACT

Coal combustion products (CCPs) are by-products created when coal is burned for energy production. In 2007 alone, the United States produced in excess of 125 million tons of CCPs. Despite the fact that approximately 40% of the CCPs were used beneficially, 60% of the CCPs were disposed of via land filling. Reusing CCPs in large volume, civil engineering applications could greatly reduce and potentially outperform the natural materials currently required for these structures, which in many cases is more economical. Recycling CCPs also reduces the carbon footprint associated with mining naturally occurring material. However, CCPs are often perceived as strictly a waste product due to their chemical composition and potentially hazardous leachate even though not all CCPs should be considered environmentally unsound. In fact, their chemical composition can vary widely depending on the source power plant location, the power plant type, and the fuel source. Therefore it is necessary that CCPs be characterized both mechanically and chemically to qualify their utilization in civil engineering structures. The missing component in the current state of practice is a consistent methodology for categorizing CCPs as either environmentally and structurally sound or harmful when used as a construction material, and this methodology should be application-based. This paper describes the development of a detailed testing framework in order to qualify the use of CCPs in large-volume civil engineering applications, in particular embankments and mine land reclamation. The testing framework is then implemented for three types of CCPs with an analysis of results.

 

TABLE OF CONTENTS

 

LIST OF TABLES ………………………………………………………………………………………………………………. viii

ACKNOWLEDGEMENTS …………………………………………………………………………………………………….. ix

Chapter 1: INTRODUCTION …………………………………………………………………………………………………… 1

Motivation ……………………………………………………………………………………………………………… 2

Objectives ………………………………………………………………………………………………………………. 3

Hypothesis ……………………………………………………………………………………………………………… 3

Chapter 2: LITERATURE REVIEW …………………………………………………………………………………………. 4

Coal Mining in Pennsylvania……………………………………………………………………………………… 4

Coal Fired Power Plants ……………………………………………………………………………………………. 6

Conventional (Pulverized) Coal Fired Power Plants ……………………………………………………….. 8

Fluidized Bed Combustion Power Plants ……………………………………………………………………. 10

Current CCP Applications ……………………………………………………………………………………….. 12

Chapter 3: PRELIMINARY TESTING FRAMEWORK ……………………………………………………………… 23

Chapter 4: MATERIALS ……………………………………………………………………………………………………….. 29

FGD Material. ……………………………………………………………………………………………………….. 29

Fluidized Bed Combustion. ……………………………………………………………………………………… 29

Class F Fly Ash. …………………………………………………………………………………………………….. 30

Chapter 5: TESTING METHODOLOGY …………………………………………………………………………………. 31

Material Characterization ………………………………………………………………………………………… 31

Scanning Electron Microscopy. …………………………………………………………………………….. 31

Particle Size Distribution. …………………………………………………………………………………….. 31

BET Specific Surface. …………………………………………………………………………………………. 31

Zeta Potential. ……………………………………………………………………………………………………. 32

Moisture/Density Relationships. ……………………………………………………………………………. 32

Specific Gravity. ………………………………………………………………………………………………… 32

Chemical Analysis …………………………………………………………………………………………………. 34

Instrumental Neutron Activation Analysis (INAA). ………………………………………………….. 34

Inductively coupled plasma mass spectroscopy (ICP-MS)………………………………………….. 34

Combustion Infrared Detection (IR). ……………………………………………………………………… 34

Mechanical Tests …………………………………………………………………………………………………… 35

Unconfined Compression Testing. …………………………………………………………………………. 35

Hydraulic Conductivity. ………………………………………………………………………………………. 36

Effluent Chemical Analysis. …………………………………………………………………………………. 37

X-Ray Diffraction. ……………………………………………………………………………………………… 38

Chapter 6: RESULTS AND DISCUSSION ………………………………………………………………………………. 39

Characterization …………………………………………………………………………………………………….. 39

Mechanical Tests …………………………………………………………………………………………………… 45

Chapter 7: RECOMMENDED TESTING FRAMEWORK ………………………………………………………….. 56

Chapter 8: CONCLUSIONS …………………………………………………………………………………………………… 58

Chapter 9: RECOMMENDATIONS FOR FUTURE WORK ……………………………………………………….. 59

REFERENCES…………………………………………………………………………………………………………………….. 60

Appendix A: HYDRAULIC CONDUCTIVITY PROCEDURE ……………………………………………………. 63

Appendix B: PROCTOR DATA ……………………………………………………………………………………………… 73

Appendix C: HYDRAULIC CONDUCTIVITY DATA ………………………………………………………………. 76

Appendix D: UNCONFINED COMPRESSION TEST DATA ……………………………………………………… 80

Appendix E: PARTICLE SIZE DISTRIBUTION DATA …………………………………………………………… 145

Appendix F: BASELINE CHEMICAL ANALYSIS …………………………………………………………………. 148

Appendix G: EFFLUENT CHEMICAL ANALYSIS ………………………………………………………………… 151

Chapter 1: INTRODUCTION

Coal combustion products (CCPs) are by-products created when coal is burned for energy production. These products include fly ash, bottom ash, boiler by-products, flue gas desulfurization (FGD) by-products, and others (ACAA, 2009). In 2007 alone, the United States produced in excess of 125 million tons of CCPs. Despite the fact that approximately 40% of the CCPs were used beneficially, for example using fly ash as a supplemental cementitious material in Portland cement concrete, 60% of the CCPs were disposed of via land filling. Figure 1 outlines the beneficial use of CCPs vs. production from 1966-2007 (ACAA, 2009). This figure clearly illustrates that the amount of CCPs being produced far exceeds the CCPs being recycled. Furthermore, the difference between the two continues to grow.

There are significant advantages to reusing CCPs for large volume civil engineering applications such as mine land reclamation and embankment structures. Currently, CCPs not beneficially used are either stockpiled or disposed of in landfills and slurry ponds. This practice consumes large quantities of land space. Reuse of CCPs, as opposed to disposal, would reserve landfills to be used for residential waste which currently has no other viable disposal methods.  Utilizing CCPs in these engineering applications could greatly reduce the amount of natural materials currently required for these structures. The excavation, transportation, and installation of natural materials have an associated cost which could potentially be significantly reduced if CCPs were used from a coal power plant in the vicinity of the construction project (Kumar and Patil, 2006). In some cases CCPs have even out-performed natural materials (Bacon, 1976). Typical intrinsic CCP properties also present various advantages. These advantages include the potential cementitious nature of CCPs (strength gain with time), low unit weight, high factor of safety for slope stability, high shear strength per unit weight ratio, and the immediate availability of large volumes of material (Butalia and Wolfe, 2001) (ACAA, 2009).

Despite their relevant advantages, CCPs are often perceived as strictly a waste product due to their chemical composition and potentially hazardous leachate. However, not all CCPs should be considered environmentally unsound. In fact, their chemical composition can vary widely depending on the source power plant location, the power plant type, and the fuel source. Therefore it is necessary that CCPs be characterized both mechanically and chemically to qualify their utilization in civil engineering structures.

In order to increase the beneficial use of CCPs, the perception of these materials as a waste product needs to be changed. Moreover, there is potential for these materials to be categorized as

“green” since CCPs have been successfully utilized in civil engineering structures. The missing component in the current state of practice is a consistent methodology for categorizing CCPs as either environmentally and structurally sound or harmful when used as a construction material, and this methodology should be application-based.  

 

Figure 1: CCP beneficial use vs. production (after ACAA, 2009)

 

 

Motivation

The motivation for this study can be summarized as follows:

  • Excess quantities of CCPs are produced annually which are not beneficially used
  • CCPS are variable depending on the type of power plant and the fuel source and must be properly examined for implementation
  • Using CCPs for large-volume, engineering applications is potentially much more economical compared to using naturally occurring materials
  • The material properties of CCPs may led to superior performance compared to other naturally occurring materials in certain applications
  • No such testing framework currently exists

 

 

Objectives

This study will focus on coal combustion products produced in the Commonwealth of Pennsylvania. The objectives of this study are to:

  1. Develop a minimal set of practical mechanical and chemical tests that will qualify CCP formulation specific to large-volume civil engineering applications. Theses parameters should provide appropriate specifications to allow the use of CCPs without negative structural or environmental impact.
  2. Apply the test framework to three distinct types of CCPs for a given application as a case study.

Hypothesis

CCPs can be evaluated in a logical, methodical manner to determine whether or not the material is usable as a civil engineering material in large-volume applications via a specific testing framework which includes characterization, chemical, and mechanical property measurements.

 

The specific questions to be addressed in this study are:

  1. What material properties (characterization, chemical, and mechanical) are required for an embankment/mine land reclamation application?
  2. Do CCPs meet the minimum requirements for use in embankments/mine land reclamation? Based on the literature review, do CCP properties have to be modified prior to use?
  3. Does FGD material, FBC Ash, and Class F fly ash meet the minimal material requirements for the given application?

TEST FRAMEWORK DEVELOPMENT FOR USE OF COAL COMBUSTION PRODUCTS (CCPS) IN EMBANKMENT CONSTRUCTION AND MINE LAND RECLAMATION

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