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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.
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THE QUANTIFICATION OF THE FLY ASH ADSORPTION CAPACITY
FOR THE PURPOSE OF CHARACTERIZATION AND USE INCONCRETE By Zeyad Tareq Ahmed
A DISSERTATIONSubmitted 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
Dissertation Advisor David W. Hand Department Chair David W. Hand Date Table of Contents List of Figures
List of Tables
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
2-2 Materials and methods
Fly ash treatment
Fly ash adsorption capacity indicators
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
3 - Air Entraining Admixtures (AEAs) Partitioning and Adsorption by Coal Fly Ash in Concrete
3-2 Materials and methods
Fly ash and AEAs
Measurement of AEA concentration
3-3 Results and discussions
AEA interaction with aggregate
AEA interaction with cement
Factors affecting AEA partitioning coefficient
Type of cement
AEA interaction with fly ash
4 - Combined Adsorption Isotherms for the Quantification of Air Entraining Admixtures Adsorption by Fly Ash in Concrete
4-2 Materials and methods.
Fly ash and AEA
Measurement of AEA concentration
Isotherm points setup
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
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
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.
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.
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
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.
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.