EVALUATION OF THE CEMENTING EFFICIENCY FACTOR OF LOW-CALCIUM FLY ASH FOR STRENGTH DEVELOPMENT AND CHLORIDE-PENETRATION RESISTANCE OF CONCRETES （コンクリートの強度発現性および塩分浸透抵抗性に関するフライアッ シュのセメント有効係数の評価） March 2021 Huynh Tan Phat EVALUATION OF THE CEMENTING EFFICIENCY FACTOR OF LOW-CALCIUM FLY ASH FOR STRENGTH DEVELOPMENT AND CHLORIDE-PENETRATION RESISTANCE OF CONCRETES （コンクリートの強度発現性および塩分浸透抵抗性に関するフライアッ シュのセメント有効係数の評価） Huynh Tan Phat A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF ENGINEERING DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING HIROSHIMA UNIVERSITY March 2021 ABSTRACT Fly ash which is a principal by-product of coal-fired power plants is used enormously due to its economic, environmental, and technical advantages. Besides the mitigation of the CO2 emission, the use of fly ash to replace a part of cement in concrete leads to (1) a reduction in the construction cost, (2) an increase of the workability of fresh concretes, (3) improvement of the mechanical and durability properties of concretes, and so on. Fly ash is known as a pozzolanic material, which possesses a little or no cementitious value. When fly ash is used to replace part of the cement in the concrete, its cementing efficiency factor (k-value) that indicates its contribution to the mechanical and durability properties of concretes has been investigated by several studies.
The quantity of the fly ash in concrete can be multiplied by the k-value to estimate the equivalent cement content, which can be added to the existing cement content for the determination of the water-to-cement ratio in the mixture. This leads to the more effective design of concrete mixture proportion that contains the fly ash as a supplementary cementitious material. Most of the proposed methods for determining the k-value of fly ash are for the compressive strength of concretes due to the simplicity and reliability of compression tests. Only a few studies have evaluated the k-value of fly ash for the durability of concretes, especially for the chloride-penetration resistances.
Additionally, the effects of cement type and water-to-binder (W/B) ratio on the k-value of fly ash for strength development of concretes have not been evaluated in a chemical approach yet. There is a lack of research evaluating the effect of fly ash reaction degree on its k-value, and the correlation between the k-value of fly ash for strength development and that for chloride-penetration resistance of concretes has not been discussed in previous studies. Therefore, the three objectives of this research are the following: (1) evaluation of the effect of cement type and W/B ratio on the k-value of fly ash for the concrete-strength development for a long period, (2) investigation in a simple approach the k-value of fly ash for the chloride-penetration resistance of concretes using the chloride- i penetration depth as a concrete-durability property (3) experimental evaluation of the effect of fly ash reactions on its k-value for the concrete-strength development and chloride-penetration resistance of concretes. In addition to these, the correlation between the k-value of fly ash for the strength and durability of the concrete is obtained.
The discussion on these evaluations would be shown by using the results of chemical analysis and/or pore structure analysis. To deal with these problems, this thesis is organized as follow: Chapter 1 provides the background and motivation of this study. Chapter 2 presents a brief review on fly ash and its k-value for the concrete-strength development and chloride-penetration resistance of concretes. Chapter 3 describes the experimental program consisting of materials and mixture proportions, the mixing, casting, and curing condition for the paste and concrete specimens.
The test procedures were conducted to evaluate the k-value of fly ash. This study uses a low- calcium fly ash which is one of the most popular fly ashes in Japan. Control concrete samples with W/B ratios of 0.60 by mass were prepared to experimentally evaluate the k-value of fly ash. Cement was partially replaced with fly ash at ratios of 20% to 40% by mass for the paste and concrete specimens with a W/B ratio of 0.
To evaluate the k-value of fly ash for the strength development of concretes, two types of cement, namely, ordinary Portland cement (OPC) and high-early-strength Portland cement (HSPC) were used for making paste and concrete specimens. In addition, a W/B ratio of 0.30 was further used for making OPC specimens to investigate effect of W/B ratio on the k-value of fly ash for the concrete- strength development. For evaluation of the k-value of fly ash for the chloride-penetration resistance of concretes, only the OPC and two fly ash replacement ratios of 20% (F20) and 40% (F40) by mass for the paste and concrete specimens with a W/B ratio of 0. A sodium chloride solution (10% NaCl) was used for the immersion test.
ii Chapter 4 investigates the effects of cement type and W/B ratio on the k-value of low- calcium fly ash for the concrete-strength development by (1) examining the degree of fly ash reaction in pastes and analyzing hydration product using the X-ray diffraction analysis, (2) evaluating the Portlandite (CH) content in pastes as well as calculating the CH consumption by the pozzolanic reaction of fly ash, and (3) determining the compressive strength of concretes. The obtained results indicate that the cement type strongly affects the k-value of fly ash for concrete-strength development because of the significant difference in the Blaine fineness between cement and fly ash as well as the difference in the relationships between cement-to- water ratio and compressive strength of the control concretes. With the presence of calcite (approximate 4% by mass) in the OPC, the stabilization of monocarbonate indirectly resulting in the stabilization of ettringite led to a more significant increase in the compressive strength of OPC concrete containing fly ash despite a low degree of fly ash reaction in OPC paste compared with HSPC paste. For OPC concrete, a lower W/B ratio has a higher k-value at the early ages mainly because of cement-hydration-enhancement effect of fly ash, and all k-values increased significantly after 28 days due to the pozzolanic reaction of fly ash.
Further, a modified equation of the CH consumption taking the cement-hydration-enhancement effect into account was firstly proposed to evaluate precisely the CH consumption in fly-ash cement paste. This result is consistent well with the result of the degree of fly ash reaction, especially for OPC paste with a low W/B ratio of 0. Chapter 5 aims at simply evaluating the k-value of low-calcium fly ash for the chloride- penetration resistance of concretes using the chloride-penetration depth (xd). The chloride concentration profile and the xd are examined, whereas the k-value of fly ash for the chloride- penetration resistance of concretes is evaluated by using the apparent diffusion coefficient (Dapp) of chloride ion as well as the xd.
Additionally, the results of pore size distribution in pastes are presented in this chapter. Results indicate that xd could be used as a concrete- iii durability property to obtain the k-value of fly ash in a simple approach compared to the Dapp. The k-values of fly ash based on the xd of the concrete after the immersion periods of 13, 26, and 39 weeks ranged from 2.69 for F20 and F40 samples, respectively. The replacement of 40% or less cement by fly ash in the concretes with a W/B ratio of 0.50 yielded chloride-penetration resistance that is as good as that of plain cement concrete with a W/B ratio of 0.30 after 39 weeks of exposure to a 10% NaCl solution with regard to the chloride-diffusion coefficient.
In addition, the results of pore size distribution in pastes indicated that the refinement effect of the fly ash reaction related to the significant reduction of the volume of pore in the diameter range of 0.33 µm could improve the chloride-penetration resistance of concretes. Chapter 6 discusses (1) the relationship between the k-value of fly ash for concrete- strength development and the degree of fly ash reaction, (2) the effect of the degree of fly ash reaction on the k-value for the chloride-penetration resistance of concretes, and (3) the difference between the k-value for the compressive strength and that for the chloride- penetration resistance. Briefly, the k-value of fly ash for the strength development of concretes increased linearly with an increase in the degree of fly ash reaction regardless of cement type and W/B ratio. Also, the k-value of fly ash based on the xd of concretes increased linearly with the increment in the degree of fly ash reaction subsequent to the start of immersion.
For OPC concretes with a W/B ratio of 0.50, the k-value of fly ash for the chloride-penetration resistance of the concrete was approximately 2.5 higher than that for the concrete-strength development at each corresponding time. Chapter 7 summaries the conclusions of this study. Recommendations for the future research are suggested as well. iv ACKNOWLEDGEMENTS First of all, I would like to express my great gratitude to my supervisor, Prof.
Kenji Kawai for giving me the continuous support and valuable guidance throughout this study. This dissertation would not have been completed without the great help, trust and patience of my supervisor. I would also like to gratefully acknowledge my co-supervisors, Prof. Kenichiro Nakarai, Prof.
Toshirou Hata, and Prof. Takaaki Ookubo for their kind assistance and supervision. I am particularly grateful to Prof. Ryoichi Sato, Dr.
Bui Phuong Trinh, Asst. Riya Catherine George, Assoc. Naser Khaji, Ms. Yoko Kuromura, Ms.
Mihoko Hayashi, my tutor (Mr. Kitagawa), my teammates (Mr. Insako, and Mr. Okamoto), the laboratory technicians (Mr.
Matsuyama and Mr. Kyoizumi), and other students of the Structural Materials and Concrete Structures Laboratory of Hiroshima University for their kind support and assistance with the experimental campaign. This research would have been impossible without the great guidance, supervision, and direct support of Asst. I would like to thank the Japanese Government (Monbukagakusho: MEXT) Scholarship Student for the funding support during my doctoral course.
Additionally, I am grateful to Hiroshima University and Ho Chi Minh City University of Technology (in Vietnam) for giving me the opportunity of this course. Finally, I sincerely thank my parents, my wife Doan Nhu Quynh, my son Huynh Nam, my sisters, and all of my family members for their love, great support, and patience during my study. Also, I would like to express my deep gratitude to my teachers, Dr. Kim Huy Hoang and senior lecturer Duong Thi Bich Huyen, for giving me the nonstop encouragement and trust.
v CONTENTS ABSTRACT i ACKNOWLEDGEMENTS v CONTENTS vi LIST OF FIGURES x LIST OF TABLES xiii CHAPTER 1: INTRODUCTION 1.2 AIMS OF THE RESEARCH 3 1.3 SCOPE OF THE RESEARCH 4 1.4 THESIS OUTLINE 5 References in chapter 1 7 CHAPTER 2: LITERATURE REVIEWS 2.1 Fly ash properties 11 2.2 Properties of fly-ash concrete 17 2.2 CEMENTING EFFICIENCY FACTOR (K-VALUE) 22 2.1 K-value of fly ash for the strength development of concretes 22 2.2 K-value of fly ash for the chloride-penetration resistance of concretes 24 2.3 SUMMARY 25 References in chapter 2 26 vi CHAPTER 3: EXPERIMENTAL PROGRAM 3.3 MIXING, CASTING AND CURING 38 3.1 Compressive strength of concretes 38 3.2 Immersion test for concrete specimens 38 3.3 Degree of fly ash reaction in pastes 40 3.4 X-ray diffraction (XRD) analysis 42 3.5 Portlandite (CH) content in pastes 42 3.6 Pore size distribution of pastes 43 3.5 SUMMARY 44 References in chapter 3 44 CHAPTER 4: EFFECTS OF CEMENT TYPE AND WATER-TO-BINDER RATIO ON THE K-VALUE OF LOW-CALCIUM FLY ASH FOR THE STRENGTH DEVELOPMENT OF CONCRETES 4.1 RESULTS OF DEGREE OF FLY ASH REACTION IN PASTES AND X-RAY DIFFRACTION ANALYSIS 47 vii 4.1 Results of degree of fly ash reaction in pastes 47 4.2 Results of XRD analysis 48 4.2 CH CONTENT AND EVALUATION OF CH CONSUMPTION IN PASTES 50 4.1 CH content in pastes 50 4.2 Evaluation of CH consumption in pastes 52 4.3 COMPRESSIVE STRENGTH OF CONCRETES AND EVALUATION OF K-VALUE OF FLY ASH FOR CONCRETE-STRENGTH DEVELOPMENT 55 4.1 Compressive strength of concretes 55 4.2 Evaluation of k-value of fly ash for the strength development of concretes 57 4.