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INNOVATIVE METHODS TO MITIGATE ALKALI-SILICA REACTION IN CONCRETE MATERIALS CONTAINING RECYCLED GLASS AGGREGATES
ABSTRACT
Application of recycled glass as a cement or fine aggregate replacement in concrete could result in major benefits towards a more sustainable design of concrete materials. This is however only possible if the main obstacle, the alkali silica reaction (ASR), is properly addressed and the ASR damage is mitigated. ASR is a deleterious reaction that occurs between meta-stable silicate phases of aggregates and hydroxyl ions present in the pore solution of portland cement concrete. With the overall goal of developing effective methods to mitigate ASR in concrete containing recycled glass, the research objectives of this PhD study are: 1- To understand the mechanisms through which fly ash controls ASR in accelerated mortar bar test (AMBT). 2- To investigate the beneficial effects of high alkali content glass powder towards ASR mitigation and elucidate the underlying ASR controlling mechanisms in AMBT 3- To perform a preliminary study of the feasibility of using Al(OH)3 as a cement replacement to control ASR . As one potential mechanism, the effect of Al on the dissolution rate of glass aggregates in alkaline solutions is further researched.
To achieve the first objective, a series of experiments were designed to assess different potential ASR mitigation mechanisms with the aid of computer modeling coupled with advanced material
characterization techniques. Various properties (e.g., pore solution composition, ion diffusion coefficient, pore size distribution, strength, ASR gel production and its composition) of mortars with the minimum required fly ash dosage were compared with 100% portland cement mortars. The findings revealed that fly ash mainly reduces the ASR expansion of mortars, by reducing the rate of ingress of the attacking hydroxyl ions from the external alkali bath. This was linked to the pore refinement occurred due to pozzolanic reaction of fly ash. With a numerical study, simulating the adsorption of alkalis by cement hydration products as a sink term, it was shown that alkali binding was also effective. Application of fly ash increased tensile strength of the mortars and thus, could enhance their resistance against cracking. Variation in ASR gel composition and alkali dilution were found to have minor effect in AMBT conditions. Finally, a new mechanism was introduced and validated in which fly ash to reduce ASR by
repressing the dissolution rate of silicate aggregates which occurs due to reduction of the effective hydroxyl ion to aggregate surface ratio.
To achieve the second research objective, four types of glass powder (GP) with different sizes were experimented in AMBT. An approximately linear relationship was obtained between GP size and the required dosage to mitigate ASR. A set of material characterization techniques was designed to shed light on the ASR suppressing effects of GP. The findings revealed that cement replacement by glass powder leads to a decrease in the pH of the pore solution even if alkalis are released from the glass powder. Based on charge balance, it was speculated that some alkalis were present in non-ionic form which do not increase the pore solution’s pH and promote ASR. Application of glass powder leads to a significant reduction in the rate of ion transport from the external bath. During the test, portlandite content of GP mortar decreased due to the pozzolanic reaction which led to a reduction in the average pore size of the binder phase of GP mortar. GP enhanced the tensile strength of the mortars which could be beneficial in ASR mitigation.
Finally, to achieve the third research objective, the replacement of 20% weight of cement with Al(OH)3 powder was shown to suppress ASR expansion during ASTM C1260 test. The study was then focused on one possible mechanism through which Al(OH)3 can mitigate ASR. The effect of soluble Al on the rate of silicate glass dissolution, at high pH was studied. Corrosion of glass slides in alkaline solutions significantly decreased in presence of Al in the solution. The cause of this phenomenon was further investigated and related to formation of a semi-crystalline Al-Si (zeolite) layer at the surface of glass slides as well as Al-poisoning of silica surface. Based on experimental results, it is speculated that the latter mechanism is more significant in reducing glass dissolution rate and the protective action of the zeolite layer is likely to be less effective. The presence of sufficient dissolved Al was found to be essential for minimizing the dissolution rate of silicate glass.
TABLE OF CONTENTS
LIST OF FIGURES ……………………………………………………………..ix
LIST OF TABLES……………………………………………………………….xv
CHAPTER 1: INTRODUCTION…………………………………………………1
1.1 The Problem of Waste Glass …………………………………………………………………………………………. 1
1.2 Alkali Silica Reaction (ASR) ………………………………………………………………………………………… 3
1.3 Research Significance and Needs: ………………………………………………………………………………….. 4
1.4 Organization of Contents ………………………………………………………………………………………………. 6
1.5 References: …………………………………………………………………………………………………………………. 9
CHAPTER 2:
BACKGROUND………………………………………………………………….10
2.1 Using Recycled Glass in Concrete: ………………………………………………………………………………. 10
2.2 Benefits of Using Recycled Glass in Concrete: ………………………………………………………………. 14
2.3 Challenges to Use of Recycled Glass in Concrete: …………………………………………………………. 16
2.4 Chemical Mechanism of ASR ……………………………………………………………………………………… 17
2.4.1 Structure of soda-lime glass ………………………………………………………………………………………… 17
2.4.2 Glass dissolution ………………………………………………………………………………………………………… 18
2.4.3 Silica gelation and swelling …………………………………………………………………………………………. 23
2.5 ASR Gel: ………………………………………………………………………………………………………………….. 25
2.6 Controlling ASR: ……………………………………………………………………………………………………….. 26
2.7 Tests to Evaluate the ASR risk of Aggregate-Cement Combinations ………………………………… 28
2.8 Summary: …………………………………………………………………………………………………………………. 33
2.9 References: ……………………………………………………………………………………………………………….. 34
CHAPTER 3: HOW DOES FLY ASH MITIGATE ALKALI-SILICA
REACTION (ASR) IN ACCELERATED MORTAR BAR TEST (ASTM
C1567)?…………………………………………………………………………………………………….38
3.1 Introduction ……………………………………………………………………………………………………………………….. 38
3.2 Existing Literature ……………………………………………………………………………………………………………… 40
3.3 Materials and Methods ………………………………………………………………………………………………………… 44
3.3.1 Accelerated mortar bar test (ASTM C1567) ………………………………………………………………….. 45
3.3.2 Pore solution extraction and analysis ……………………………………………………………………………. 46
3.3.3 Measurement of ion diffusivity using electrical impedance spectroscopy ………………………….. 47
3.3.4 Tensile and compressive strength tests ………………………………………………………………………….. 48
3.3.5 SEM/EDS imaging …………………………………………………………………………………………………….. 49
3.3.6 Aggregate dissolution rate measurements ……………………………………………………………………… 50
3.3.7 Numerical Model to Simulate Alkali Transport and Binding …………………………………………… 51
3.4 Results and Discussion ……………………………………………………………………………………………………….. 53
3.4.1 Sufficient dosage of fly ash to mitigate ASR …………………………………………………………………. 53
3.4.2 Pore solution composition …………………………………………………………………………………………… 55
3.4.3 Ion diffusion coefficient ……………………………………………………………………………………………… 59
3.4.4 Significance of alkali diffusion versus binding ………………………………………………………………. 61
3.4.5 Tensile and compressive strength …………………………………………………………………………………. 63
3.4.6 Microstructural analysis (SEM/EDS) ……………………………………………………………………………. 65
3.4.6.1 Source of alkalis: ……………………………………………………………………………………………………….. 68
3.4.7 Aggregate dissolution rate …………………………………………………………………………………………… 70
3.5 Conclusions ……………………………………………………………………………………………………………………….. 72
3.6 References …………………………………………………………………………………………………………………………. 74
CHAPTER 4: ASSESSING THE ROLE OF ION TRANSPORT IN MITIGATION OF ASR BY FLY ASH IN ASTM C1567…….………………78
4.1 Introduction ……………………………………………………………………………………………………………………….. 78
4.2 Research Significance …………………………………………………………………………………………………………. 80
4.3 Materials and Methods ………………………………………………………………………………………………………… 81
4.3.1 More details on measuring the electrical conductivity of mortars: ……………………………………. 82
4.3.2 Porosity of pastes and mortars: …………………………………………………………………………………….. 85
4.3.3 Pore Size Distribution (PSD) characterization: ………………………………………………………………. 85
4.4 Results and discussion ………………………………………………………………………………………………………… 87
4.4.1 Composition of the binder to mitigate ASR …………………………………………………………………… 87
4.4.2 Pore solution composition …………………………………………………………………………………………… 90
4.4.3 Ion transport ………………………………………………………………………………………………………………. 97
4.4.4 Porosity: ………………………………………………………………………………………………………………….. 102
4.4.5 Pore size distribution: ……………………………………………………………………………………………….. 105
4.5 Conclusions ……………………………………………………………………………………………………………………… 106
4.6 References: ………………………………………………………………………………………………………………………. 108
CHAPTER 5: INVESTIGATING ASR MITIGATING MECHANISMS OF GLASS POWDER IN ASTM C1567 ACCELERATED TEST..………..111
5.1 Introduction ……………………………………………………………………………………………………………………… 111
5.2 Materials and Methods ………………………………………………………………………………………………………. 113
5.2.1 Accelerated mortar bar test (ASTM C1567) ………………………………………………………………… 115
5.2.2 Pore solution extraction and analysis ………………………………………………………………………….. 116
5.2.3 Pore size distribution characterization …………………………………………………………………………. 116
5.2.4 Pozzolanic reaction of glass powder: ………………………………………………………………………….. 116
5.3 Results and discussion: ……………………………………………………………………………………………………… 117
5.3.1 Sufficient dosage of glass powders to mitigate ASR …………………………………………………………. 117
5.3.2 Tensile and compressive strengths ………………………………………………………………………………….. 120
5.3.3 Pore solution composition of ASTM C1567 mortars ………………………………………………………… 122
5.3.4 Long term pH of pore solution of cement pastes ………………………………………………………………. 127
5.3.5 Ion diffusion coefficient of mortars ………………………………………………………………………………… 129
5.3.6 Porosity, pore connectivity and pore size distribution ……………………………………………………….. 131
5.3.7 Portlandite consumption ……………………………………………………………………………………………….. 133
5.3.8 Microstructural analysis (SEM/EDS) ……………………………………………………………………………… 134
5.3.9 Reducing silica dissolution rate from aggregates ……………………………………………………………… 137
5.4 Conclusions ……………………………………………………………………………………………………………………… 138
5.5 References: ………………………………………………………………………………………………………………………. 140
CHAPTER 6: INVESTIGATING THE USE OF Al(OH)3 AS
AN ASR SUPPRESSOR: EFFECT ON THE DISSOLUTION
RATE OF SODA-LIME GLASS……………………………………………..142
6.1 Introduction ……………………………………………………………………………………………………………………… 142
6.2 Research significance ………………………………………………………………………………………………………… 144
6.3 Materials and methods ………………………………………………………………………………………………………. 145
6.4 Results …………………………………………………………………………………………………………………………….. 148
6.4.1 ASR expansion in ASTM C1260 ……………………………………………………………………………………. 148
6.4.2 Dissolution rate of silica glass slides ………………………………………………………………………………. 150
6.4.2.1 Dissolution of Al(OH)3 in high alkaline aqueous solutions ……………………………………………. 150
6.4.2.2 Mass loss measurement of glass slides and the solution analysis …………………………………….. 153
6.4.2.3 Dissolution of glass slides in solutions containing finite [Al] …………………………………………. 159
6.4.3 Surface ccharacterization of the corroded glass slides ……………………………………………………….. 162
6.5 Discussion ……………………………………………………………………………………………………………………….. 168
6.6 Conclusion ………………………………………………………………………………………………………………………. 170
6.7 References ……………………………………………………………………………………………………………………….. 172
CHAPTER 7: SUMMARY, CONCLUSIONS AND
FUTURE DIRECTIONS………………………………………………………173
7.1 Summary …………………………………………………………………………………………………………………………. 175
7.2 conclusions of the research on the role of fly ash in ASR mitigation ……………………………………….. 176
7.3 conclusions of the research on the beneficial effect of glass powder against ASR …………………….. 179
7.4 conclusions of the study on the feasibility of using Al(OH)3 as an ASR suppressor …………………… 180
7.5 Suggestions for future research …………………………………………………………………………………………… 181
CHAPTER
ONE
INTRODUCTION
1.1 The Problem of Waste Glass
The growing of stockpiles of post-consumer recycled glass (e.g., bottles, window plates) is a major concern for municipalities in many states and countries. This problem is more urgent in locations with limited land (e.g., Hawaii) or large population density (e.g., North-East corridor of
- US) and has led to increasing disposal costs for both consumers and local governments. According to the most recent US-EPA report [1] , from approximately 250 million tons of municipal solid waste generated in 2010 in the United States, 4.6% (approximately 11.53 million tons) was waste glass. Out of this volume, 27.1% (about 3.13 million tons of glass) was recovered by recycling facilities. Even so, ultimately ~600,000 tons out of that is not actually recycled into new glass [2] . The main obstacle against glass to glass recycling is the potentially high cost of shipping glass, from collecting points to remelting facilities (which could be few hundred kilometers apart); and this has made the economics of glass recycling unattractive. In addition, waste glass stockpiles are often contaminated (e.g., by sugar, paper, and other organics) and mixed in color which makes them less suitable for reuse in glass making industry. These factors have led to continual stockpiling of waste glass and its subsequent environmental impacts (Figure 1.1).
Other than the ideal use of recycling glass for manufacturing new glass, secondary applications of recycled glass such as in abrasives, glass wool, or as water filtration media have been developed [4] . Lately, it has been attempted to utilize waste glass in construction materials such as bricks and ceramics [5] and enhanced night visible asphalt [6] .
Figure 1.1: Stockpile of waste glass, Huntington, West Virginia, USA [3]
Due to enormous volume of concrete produced annually (estimated worldwide at 11 billion tons/year) [7] , incorporation of recycled glass in concrete has a great potential to convert large quantities of collected glass into a value-added material. Substitution of waste materials will conserve limited natural resources (used for production of cement and aggregate) and will mitigate the environmental and ecological damages caused by quarrying and exploitation of raw materials for making concrete.
From an engineering standpoint, concrete is designed to fulfill certain mechanical properties and satisfy specific durability performance during its service life. Fortunately, application of glass as concrete fine aggregate has not been found to have a major impact on mechanical properties of concrete [8] . However, the exposure of amorphous silicate in glass to high alkaline environment of concrete can result in an alkali-silica reaction (ASR). As a result of this reaction, an alkalisilica gel is produced which absorbs water, swells and exerts tensile stresses inside concrete. These stresses can result in cracks and damages in concrete which shortens the effective service life of the structure.
1.2 Alkali Silica Reaction (ASR)
Alkali silica reaction has long been a major durability problem in concretes containing reactive natural aggregates (e.g., sandstone, argillite, chert, opal, greywacke). Aggregates containing metastable silicates can react with the hydroxyl ions of the concrete pore solution. As a result of this reaction, a silicate gel is produced. This gel is hygroscopic and imbibes available moisture from the interior of concrete and expands. A deleterious expansion for concrete is regarded as 0.04% to 0.05% expansion [9] . The swelling pressure is sufficient to disrupt the fabric of concrete and induce expansions higher than the tensile strain capacity of concrete. Since the reactive aggregates are distributed in the bulk of concrete, generally this reaction leads to a map cracking at the member’s surface with gel exudation which is a common characteristic and feature of ASR (Figure 1.2)
(a) (b)
Figure 1.2: (a) Extensive map cracking in concrete barriers along State Highway 2 near Leominster, MA. (b) Gel staining around cracks in the parapet wall of a bridge structure affected by ASR [10]
1.3 Research Significance and Needs:
Recycling glass is a major problem for municipalities across the world. Utilizing glass as aggregate/cement replacement in concrete is a potential solution if the deleterious ASR is controlled. The present study aims at expanding the knowledge related to the ASR mitigation in concretes containing recycled glass. Study of ASR using glass as reactive aggregate has the added benefit of simplifying the investigations by studying the physical and chemical reactions using a homogeneous and isotropic reactive material comparing to natural reactive aggregates which are mostly composed of different phases and are orthotropic. For example, the effect of aggregate composition on ASR performance can be examined by experimenting glasses with various compositions (e.g. aluminosilicate glass, borosilicate glass,etc). In addition, it would be possible to take advantage of the available literature on glass corrosion to gain a better understanding of durability of silicate glasses in alkaline environment of concrete. It is also possible to advance ASR knowledge towards developing new materials and admixtures to mitigate ASR. After a review of the available literature on developing glass-based concrete materials, the following research needs were identified to be further studied in the present work:
- Previous research has recommended application of supplementary cementitious materials
(SCM) (e.g, fly ash) to control ASR. However, it is unclear how fly ash and other SCMs mitigate ASR (i.e. what are the mechanisms involved) and what fly ash properties most significantly determine its efficiency against ASR. There is specifically a knowledge gap with regards to role of fly ash and other SCMs during accelerated ASR performance tests. In these tests, ASR is artificially accelerated by submerging concrete or mortar bars in high alkaline solutions (e.g., 1M NaOH) at high temperatures (e.g. 80°C). As such, the role of fly ash in mitigating ASR could be through reduction of mass transport properties of concrete, dilution and binding of alkalis, increasing the resistance of concrete to cracking, or a combination of these and other factors.
These mechanisms are studied in chapters 3 and 4 of this document.
- Previous experiments have shown that soda-lime glass powder is pozzolanic and may be capable of controlling ASR. However, high sodium content of glass powder is a concern in promoting rather than inhibiting ASR. Also, it is unclear if reducing the size of glass powder is beneficial towards improving its pozzolanic reactivity or in contrast, leads to higher alkali release rate and promotes ASR. Chapter 5, attempts to clarify the underlying mechanisms in ASR mitigation of glass powder to address these questions.
- There is a need for development of more efficient and less costly admixtures to inhibit ASR in concrete. Earlier research on glass corrosion suggests that the presence of Al can slow down the dissolution rate of glass in alkaline media. This is important from an ASR perspective as Al has the potential to cease ASR at its very first step. While there have been some recent studies focusing on the effect of the Al content of different pozzolanic materials on their efficiency to suppress ASR (e.g., metakaoline, fly ash), the feasibility of using Al compounds independently as an ASR inhibitor is a novel idea. This is the main focus of chapter 6. Studying Al compounds not only sheds light on the exact role of Al content of pozzolans, but also may lead to the development of new additives or cement replacements to avoid ASR in future concrete
structures.
1.4 Organization of Contents
This study focuses on characterizing and developing innovative methods to mitigate ASR in concrete, especially where recycled glass is used as fine aggregates. Chapter 2 provides a background on the use of recycled glass in concrete. Challenges and benefits are introduced. The alkali-silica reaction is reviewed and conventional methods for mitigation of ASR are explained. Tests that have been suggested to predict the ASR potential of aggregates or to determine the effectiveness of mineral and chemical admixtures in mitigation of ASR are presented.
Chapter 3 investigates the mechanisms by which coal fly ashes reduce ASR. A broad series of analytical techniques are used to study the mechanisms of ASR mitigation in mortars containing glass aggregates and tested under the environmental conditions specified by ASTM C1567, accelerated mortar bar test.
The findings in chapter 3 revealed that reducing ion transport is one of the dominant mechanisms which enables fly ash to reduce ASR during ASTM C1567 test. As such, chapter 4 focuses on characterizing the transport properties of mortars containing a sufficient dosage of fly ashes to mitigate ASR and compares these properties with those of 100% portland cement mortars or the mortars containing a lower dosage of the same fly ash. In addition, the dosage of different fly ashes that is sufficient in suppressing ASR in mortars with recycled glass aggregates are obtained and related to the chemical composition of fly ash.
Chapter 5 investigates the capacity of soda-lime glass powder as an ASR inhibitor. Glass powder exhibits pozzolanic behavior (more significant for smaller particle sizes) and can be used as partial cement replacement to mitigate ASR of glass aggregates or natural reactive aggregates. Powders with different particle size distributions are studied according to ASTM C1567 and the proper contents to mitigate ASR are obtained. Further investigations are performed to understand the mechanisms through which glass powder reduces ASR expansions.
Chapter 6 presents a preliminary study to investigate the feasibility of using amorphous aluminum hydroxide to control ASR. Specifically, the focus is to understand the mechanisms by which aluminum slows down the dissolution rate of silicate glass is high alkaline environment.
Chapter 7 provides a summary of the findings and conclusions of this Ph.D. study. Based on the results, areas for future research are identified to improve the knowledge on ASR mechanisms and its mitigation.
1.5 References:
- http://www.epa.gov/osw/nonhaz/municipal/pubs/msw_2010_rev_factsheet.pdf
- Reindl, Reuse/recycling of glass cullet for non-container uses. 2003, Wisconsin Department of Public Works: Madison, WI (www.epa.gov/osw/conserve/rrr/greenscapes /pubs/glass.pdf).
- http://www.corbisimages.com/stock-photo/rights-managed/JA004525/bucket-loader-at-green-glassstockpile/?tab=details&caller=search.
- Idir, M. Cyr and A. Tagnit-Hamou, Use of fine glass as ASR inhibitor in glass aggregate, Construction and Building Materials, 2010, 24, 1309-1312.
- F. Youssef, M. F. Abadir and M. Shater, Utilization of soda glass (cullet) in the manufacture of wall and floor tiles, Journal of European ceramic society 1998, 18, 1721-1727.
- D. Pascoe, R. W. Barley and P. R. Child, Autogenous grinding of glass cullet in a stirred mill. In: Proceedings of the International Symposium Recycling and Reuse of Glass Cullet. Dundee: Thomas Thelford; 2001, 15-27.
- K. Mehta, P. J. M. Monteiro, concrete: Microstructure, Properties and Material, 3rd edition, McGraw Hill, New York , 2006.
- B. Topcu and M. Canbaz, Properties of concrete containing waste glass, Cement and Concrete Research, 2004, 34, 267-274.
- W. Hobbs, Deleterious expansion of concrete due to alkali-silica reaction: influence of Pfa and slag, Magazine of Concrete Research, 1986, 38(137), 191-205.
- http://en.wikipedia.org/wiki/File:ASR_cracks_concrete_step_barrier_FHWA_2006.jpg.
- Shao, T. Lefort, S. Moras and D. Rodriguez, Studies on concrete containing ground waste glass, Cement and Concrete Research, 2000, 30(1), 91-100.
- Oka and M. Tomozawa, Effect of alkaline-earth ion as an inhibitor to alkaline attack on silica glass, Journal of Non-Crystalline Solids, 1980, 42(1-3), 535-543.
- Y. Hong, F.P.Glasser, Alkali sorption by C-S-H and C-A-S-H gels: Part II. Role of alumina, Cement and Concrete Research, 2002, 32(7), 1101-1111.
