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«Michigan Technological University Digital Commons Michigan Tech Dissertations, Master's Theses and Master's Reports Dissertations, Master's Theses ...»

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THE QUANTIFICATION OF THE FLY ASH

ADSORPTION CAPACITY FOR THE

PURPOSE OF CHARACTERIZATION AND

USE IN CONCRETE

Zeyad Tareq Ahmed

Michigan Technological University Copyright 2012 Zeyad Tareq Ahmed Recommended Citation Ahmed, Zeyad Tareq, "THE QUANTIFICATION OF THE FLY ASH ADSORPTION CAPACITY FOR THE PURPOSE OF CHARACTERIZATION AND USE IN CONCRETE", Dissertation, Michigan Technological University, 2012.

http://digitalcommons.mtu.edu/etds/789 Follow this and additional works at: http://digitalcommons.mtu.edu/etds Part of the Civil Engineering Commons, and the Materials Science and Engineering Commons

THE QUANTIFICATION OF THE FLY ASH ADSORPTION CAPACITY

FOR THE PURPOSE OF CHARACTERIZATION AND USE IN

CONCRETE By Zeyad Tareq Ahmed

A DISSERTATION

Submitted in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY

(Environmental Engineering)

MICHIGAN TECHNOLOGICAL UNIVERSITY

© 2012 Zeyad Ahmed This dissertation “The Quantification of the Fly Ash Adsorption Capacity for the Purpose of Characterization and Use in Concrete,” is hereby approved in partial fulfillment of the requirement for the Degree of DOCTOR OF

PHILOSOPHY IN ENVIRONMENTAL ENGINEERING.

Department of Civil and Environmental Engineering

Signatures:

Dissertation Advisor David W. Hand Department Chair David W. Hand Date Table of Contents List of Figures

List of Tables

Preface

Acknowledgement

Abstract

1 - Introduction

1-1 Fly ash and Fly ash production

1-2 Fly ash in Concrete

1-3 Air Entraining Admixtures (AEAs).

1-4 Interaction between fly ash and AEAs

Factors affecting AEA adsorption on fly ash carbon

1-5 Measurement of the adsorption capacity of fly ash

The fly ash carbon content

The foam index test

Foam index test and LOI

2 - Fly Ash Iodine Number for the Measurement of the Adsorption Capacity of Coal Fly Ash

2-1 Introduction

2-2 Materials and methods

Materials

Fly ash treatment

Fly ash adsorption capacity indicators

Adsorption isotherms

Mass of fly ash

Adsorption isotherms setup

Iodine concentration measurement

2-3 Results and discussion

Impact of the fly ash treatment

Adsorption capacity indicators

Initial concentration of iodine

Iodine adsorption isotherms

The target iodine concentration selection

2-4 Conclusions

3 - Air Entraining Admixtures (AEAs) Partitioning and Adsorption by Coal Fly Ash in Concrete

3-1 Introduction

3-2 Materials and methods

Fly ash and AEAs

Measurement of AEA concentration

Isotherm setup

3-3 Results and discussions

AEA interaction with aggregate

AEA interaction with cement

Factors affecting AEA partitioning coefficient

AEA concentration

Type of cement

AEA interaction with fly ash

Adsorption isotherms

3-4 Conclusions

4 - Combined Adsorption Isotherms for the Quantification of Air Entraining Admixtures Adsorption by Fly Ash in Concrete

4-1 Introduction

4-2 Materials and methods.

Fly ash and AEA

Measurement of AEA concentration

Isotherm points setup

Cement blanks

COD of solid materials

Fly ash isotherm points

4-3 Results and discussions

Test development and optimization

Combination isotherm calculations

Combined Cement and Fly Ash Isotherm Results Analysis.................. 83 Adsorption Isotherms Utilization and AEA Dosage Adjustment........... 84 Effect of Temperature on Fly Ash Adsorption Capacity

Results Verification

4-4 Conclusions and recommendations

5 - Summary and conclusions

5-1 LOI Correlation to the Adsorption Tests

5-2 Correlation among the adsorption capacity tests

The foam index and the fly ash capacity

The fly ash iodine number and the fly ash capacity

5-3 Conclusions

References

Appendix A. Direct adsorption isotherms results for various AEAs.............. 104 Appendix B. Copyright permissions

List of Figures

Figure 1.1 Particle size distribution for various fly ash specimens

Figure 1.2 SEM image of fly ash at 2000X magnification.

Figure 1.3 Air entraining admixture chemical nature

Figure 1.4 Mechanism of air entraining

Figure 1.5 AEA adsorption on fly ash carbon.

Figure 1.6 Foam index test versus LOI for five different studies

Figure 1.7 Specific foam index test versus LOI for the studies presented in Figure 1.





6.

Figure 2.1.

The effect of multiple treatment cycles on the adsorption behavior of fly ash

Figure 2.2 Correlation between LOI and foam index tests results for the fourteen fly ash types studied.

Filled data points were chosen to illustrate inconsistencies between the LOI and foam index test results................ 37 Figure 2.3 Effect of iodine solution concentration on the adsorption isotherm results for the 6.

06 % LOI fly ash.

Figure 2.4 Aqueous phase iodine concentration versus fly ash mass for (a)

0.05N and (b) 0.025N initial iodine solution concentration. LOIs are shown in parentheses.

Figure 2.5 Adsorption isotherms for (a) 0.

05N and (b) 0.025N iodine with 10 of fly ash types. LOIs are shown in parentheses.

Figure 2.6 The fly ash iodine number with target concentrations of 0.

01N and

0.005N versus (a) LOI and (b) foam index for 10 types of fly ash........ 43 Figure 2.7 Fly ash iodine number at 0.

01N and 0.005N versus LOI................ 44 Figure 2.8 Correlation between LOI and fly ash iodine number

Figure 3.1 The correlation between AEA concentration in % Vol.

and COD (mg/L)

Figure 3.2 AEAs partitioning between cement and water

Figure 3.3 AEA partitioning coefficient for various AEA concentrations.

...... 58 Figure 3.4 Effect of type of cement on the AEA partitioning coefficient......... 60 Figure 3.5 Low carbon fly ash (0.

39% LOI) interaction with three types of AEAs

Figure 3.6 Interaction between high carbon fly ash and six different AEAs, AEAs concentrations expressed as mg/L of COD

Figure 3.7 Interaction between high carbon fly ash and six different AEAs, AEAs concentrations expressed as ratio to the initial AEA concentration (C/Co)

Figure 3.8 AEA cement partitioning coefficients for six AEAs at various concentrations equilibrated with 20 g of portland cement.

Figure 3.9 High carbon fly ash isotherm with 0.

8% MB VR

Figure 3.10 High carbon fly ash isotherm results with six AEAs.

Figure 3.11 High carbon fly ash isotherm results with six AEAs.

Capacity expressed as ml AEA per g fly ash and concentration as %vol. in water

Figure 4.1 Combination isotherm results of 0.

8% MB VR, fly ash 39, and various masses of portland cement

Figure 4.2 Combined adsorption isotherms for MB-VR with eight fly ashes.

. 84 Figure 4.3 The effect of temperature on the adsorption capacity of fly ash..... 86 Figure 5.1 LOI correlation to fly ash iodine number, foam index, and fly ash capacity measured using the direct adsorption isotherms.

Figure 5.2 The relationship between the fly ash iodine number, the foam index, and the capacity of fly ash at 0.

4% vol. MB VR concentration measured using direct adsorption isotherms

Figure 5.3 The correlation between the fly ash iodine number and various concentrations of the vinsol resin admixture MB VR

List of Tables Table 2.1 Selected fly ash specimens and their properties

Table 2.2 Freundlich isotherm parameters for 0.

025N iodine isotherms with 14 types of fly ash

Table 2.3 Results of the fly ash iodine number, LOI, and the foam index for the 14 types of fly ash

Table 3.1 Fly ash specimens and their properties

Table 3.2 AEAs used in this study

Table 4.1 Fly ash specimens and their properties

Preface

This research project is part of a National Cooperative Highway Research Program (NCHRP 18-13) funded by the Transportation Research Board of The National Academies. Chapter two, three, and four of this dissertation are to be submitted as journal publications upon the approval of the final project report.

The author of this dissertation has conducted the laboratory work, analyzed, and collected all the data presented in this dissertation.

Acknowledgement

I wish to express my gratitude to my advisor, Dr. David Hand for his guidance and close supervision. I would like to thank him for his generosity in sharing his expertise, willingness to teach, and mostly his patience during my studies. His help and friendship turned this research into a pleasant journey, and I will remain his student who is eager to learn more from him for the rest of my life.

I would like to thank my committee members, Dr. Neil Hutzler, Dr. Martin Auer, Dr. Lawrence Sutter, and Dr. Stephan Hackney for taking interest in my work and for their assistance and valuable suggestions.

I am very grateful to Mrs. Shelle Sandell for her help and support which affected my work, study and my life at the MTU. I would like to thank Mr.

David Perram for his scientific and technical support.

I would like to thank The National Cooperative Highway Research Program, the Transportation Research Board of The National Academies for funding this project (NCHRP 18-13). I also like to thank the National Science Foundation for granting me S-STEM scholarship (Grant No. 0806569) for two years.

I am also very grateful to my friends who supported me during tough times especially Mike, Meredith, and Melanie, and to my family especially my wife Hala for her unlimited encouragement and support.

Abstract Fly ash has been shown to be an effective replacement for portland cement in concrete mixtures. However, many fly ash materials contain unburned carbon from the combustion process. Unburned carbon in fly ash adsorbs air entraining admixtures (AEAs) reducing their effectiveness in providing a specified air void system in concrete materials. Measurement tools and methods for characterization of the adsorption properties of fly ash materials are necessary for beneficial use of fly ash materials in concrete. In this research, two methods were developed to measure and quantify the adsorption capacity AEAs on fly ash materials. The first method is the fly ash iodine number, a simple laboratory procedure that measures the adsorption capacity of fly ash based on iodine adsorption. The second is the application of direct adsorption isotherms. This test can be used to quantify the amount of AEA adsorbed by fly ash in concrete.

When the iodine number test is combined with the direct adsorption isotherms, the AEAs dosage predictions can be made by simply measuring the fly ash iodine number of the fly ash, then use the fly ash iodine number-direct adsorption correlation to predict the amount of AEA adsorbed, which represent the required dosage adjustment.

These two tests provide a robust, simple, and practical methodology for engineers to use in the specification of AEA quantities required for concrete mixes when Portland cement is replaced by fly ash.

1 - Introduction More than one fourth of the world production of primary energy is from coal (1). In 2010, the United States produced 4.13 billion megawatthours of electricity with 1.85 billion megawatthours from coal (2), generating 67.7 million tons of fly ash. Only 38% of this fly ash was beneficially used (3), the remainder was land filled as solid waste.

Currently the primary market for fly ash utilization is for use in concrete to improve durability and to reduce the amount of portland cement used in concrete mixtures. Increased fly ash utilization in concrete is challenged and limited by the tendency of fly ash to adsorb organic chemicals, most notably air entraining admixtures (AEAs), thereby adversely affecting other concrete properties. This adsorption property, on the other hand, can be favorable for other uses for fly ash. In both cases, the lack of an adequate test method to assess fly ash adsorption capacity limits increased fly ash use.

Air entraining admixtures interact with cement, aggregate, and fly ash in a complex manner due to the complex composition of AEAs and to the presence of various types of minerals in the concrete mix. Residual carbon in the fly ash adsorbs some components of the AEAs, reducing their availability to function in the concrete mixture, leading to a failure to produce the required air content in the concrete (4) (5) (6) (7) (8) (9). Implementing low temperature combustion techniques to reduce the mono-nitrogen oxides (NOx) emissions has increased the amount of unburned carbon and introduced high adsorption capacity fly ashes (10) (11). The adsorption capacity of fly ash is governed not only by the amount of carbon content but also by other properties such as the particle size, surface chemistry, and positioning of carbon in the fly ash particle.



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