Geopolymer, green chemistry and sustainable development solutions

Geopolymer, Green Chemistry and Sustainable Development Solutions

GŽopolymère, Chimie Verte et Solutions pour le DŽveloppement Durable

Edited by Joseph Davidovits

Proceedings of the World Congress Geopolymer 2005 Rapports du Congrès Mondial GŽopolymère 2005

© 2005 Geopolymer Institute

Published by: Institut Géopolymère 16 rue Galilée F-02100 Saint-Quentin France Web: www.geopolymer.org Edited by: Joseph Davidovits Web: www.davidovits.info All Rights Reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording or any other information storage and retrieval system, without prior permission in writing from the publisher. Tous Droits Réservés. Aucune partie de cette publication ne peut être reproduite sous aucune forme ou par aucun moyen, électronique ou mécanique, incluant la photocopie, l’enregistrement ou par système de stockage d’informations ou de sauvegarde, sans la permission écrite préalable de l’éditeur. 2

Geopolymer: green chemistry and sustainable development solutions

Foreword This book represents selected contributions offered to the World Congress Geopolymer 2005, fourth international conference on geopolymers. All papers have been subjected to peer review process under the Geopolymer Institute publication policy. As a tribute to Prof. Dr. Joseph Davidovits’ 70th birthday in 2005, and the 25th anniversary of the first geopolymer patents, (Na-K)-PSS types, the World Congress Geopolymer 2005 gathered two major events in two different locations: 1) Fourth International Conference!, at Saint-Quentin, France, !June 29, 30, and July 1, 2005!! 2) International Workshop on Geopolymer Cements and Concrete!, Perth, Australia!, September 28-29, 2005 The main topic of the congress was "Geopolymer-chemistry and sustainable development.; the Poly(sialate)terminology, a very useful and simple model for the promotion and understanding of green-chemistry". The last few years have seen spectacular technological progress in the development of geosynthesis and geopolymeric applications. More and more public and private research institutes and companies are working on this new chemistry for innovative solutions in adding value on industrial wastes, or solutions to emit less pollution, more careful on the environment and mankind, respecting the sustainable development and the 3 bottom line principles. Also, remarkable achievements made through geosynthesis and geopolymerisation include mineral polymers (geopolymers), flexible ceramics which transform like plastics at low temperatures, ceramic composite made manually at room temperature or thermoset in a simple autoclave, concrete which after 4 hours has higher strength than the best currently-used concrete. This cement is clean and green. It emits up to 90% less CO2 than classical Portland cement, and it is the safest toxic and nuclear waste-containment material. Geopolymers enable product designers to envisage the use of ceramic type materials with the same facility as organic polymers, or cement with the same ease of use as Portland cement. This new generation of materials, whether used pure, with fillers or reinforced, is already finding applications in all fields of industry. These applications are to be found in civil engineering, plastics industries, waste management, automotive and aerospace industries, non ferrous foundries and metallurgy, etc.

Avant p ropos Ce livre est une sélection des contributions présentées au Congrès Mondial Géopolymère 2005, quatrième conférence internationale sur les géopolymères. Tous les articles ont subit un processus d'évaluation par les pairs conformément aux règles de publication de l'Institut Géopolymère. En hommage au 70e anniversaire du Prof. Dr. Joseph Davidovits en 2005 et au 25e anniversaire du premier brevet sur les géopolymères de types (Na-K)-PSS, le Congrès Mondial Géopolymère 2005 rassembla deux événements en deux endroits: 1. Quatrième Conférence Internationale, à Saint-Quentin, France, 29 juin au 1 juillet 2005, 2. Atelier International sur les ciments et béton géopolymères à Perth, Australie, 28 et 29 septembre 2005. Le thème de ce Congrès était: "la chimie des géopolymères et le développement durable; la terminologie Poly(sialate), un modèle simple et utile pour la promotion et la compréhension de la chimie verte". Ces dernières années ont vu des progrès technologiques spectaculaires dans le développement de la géosynthèse et des applications géopolymériques. De plus en plus de sociétés, d'instituts de recherches privés et publiques travaillent sur cette nouvelle chimie proposant des solutions innovantes, notamment dans la valorisation des déchets industriels (pouvant servir de matière première ou recyclable), ou dans des solutions de productions moins polluantes, plus attentives à l’environnement et aux hommes, et respectueuses des principes du développement durable. En outre, les remarquables accomplissements réalisés par la géosynthèse et la géopolymèrisation incluent les polymères minéraux (géopolymère), céramiques flexibles qui se transforment comme des plastiques à basse température, composites céramiques faits manuellement à température ambiante ou thermodurcie dans un simple autoclave, un béton qui, après quatre heures, a une plus haute résistance que le béton normal. Ce ciment est propre et vert. Il émet jusqu'à 90% moins de CO2 que le ciment Portland classique, et c'est le matériau le plus sûr pour le stockage de déchets toxiques et nucléaires. Les géopolymères permettent à des concepteurs de produits d'envisager l'utilisation de ce type de matériaux céramique avec la même facilité que les polymères organiques, ou le ciment avec la même simplicité d'utilisation que le ciment Portland. Cette nouvelle génération de matériaux qu'elle soit utilisée pure, chargée ou renforcée, trouve des applications dans tous les domaines de l'industrie. Ces applications se rencontrent dans l'industrie du bâtiment, automobile, aérospatiale, aviation, fonderie et métallurgie, les plastiques, le stockage des déchets, etc.

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The conference Geopolymer 2005 held in Saint-Quentin, France, could not have taken place without the financial support of: La conférence Géopolymère 2005, tenue à Saint-Quentin, France, n'aurait pu avoir lieu sans le soutien financier de: - Ville de Saint-Quentin (City of Saint-Quentin), - S.D. Hans-Adam II, Prince of Liechtenstein - Conseil Régional de Picardie (Picardy Regional Council) - Union des Industries Chimiques, UIC (French Chemical Industries Union) - Cordi-Géopolymère International Organisation Committee Comité d'Organisation International - Professor Joseph Davidovits, President of the Geopolymer Institute, Saint-Quentin, France - Professor B. Vijay Rangan, Prof. of Civil Engineering, Faculty of Eng & Comp, Curtin University of Technology, Perth, Australia - Dr. Grant Lukey, General Manager of Siloxo, Senior Research Fellow, Department of Chemical Engineering, University of Melbourne, Australia - Professor Claude James, INSSET, University of Picardie, Saint-Quentin, France - Ralph Davidovits, President of CORDI-Géopolymère, Saint-Quentin, France

The International Workshop on Geopolymer Cements and Concrete!, Perth, Australia!, could not have taken place without the financial support of: L'Atelier International sur les ciments et béton géopolymères à Perth, Australie, n'aurait pu avoir lieu sans le soutien financier de: - The University of Alabama in Huntsville, USA - Curtin University of Technology in Perth, Australia - National Science Foundation of the USA International Organisation Committee Comité d'Organisation International - Professor B. Vijay Rangan, Prof. of Civil Engineering, Faculty of Eng & Comp, Curtin University of Technology, Perth, Australia - Professor Houssam Toutanji, University of Alabama in Huntsville, USA

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Effect of Mechan ically Activ ated Fly ash on the P rop erties of Geopolymer Cem ent Effet des cendres volantes mécaniquement activées sur les propriétés du ciment Géopolymère

Sanjay Kumar, Rakesh Kumar, T.C. Alex, A. Bandopadhyay, S.P. Mehrotra National Metallurgical Laboratory Council of Scientific & Industrial Research Jamshedpur – 831 007, India

Abstract: Effect of mechanical activation of fly ash on the structure and properties of geopolymer cement has been investigated. High energy milling devices, namely attrition and vibratory mills, were used for mechanical activation. The alkali activators for the geopolymerisation reaction included sodium silicate and sodium hydroxide. A lowering of geopolymerisation reaction temperature was observed due to increase in the reactivity of fly ash by mechanical activation. Geopolymers prepared using mechanically activated fly ash showed greater amount of geopolymer product, compact structure and remarkably higher strength as compared to raw fly ash based geopolymers. The effect of mechanical activation is found to be mill specific and, a suitable combination of the mill and alkali activator is required to realize the beneficial effect on mechanical properties of the geopolymer. L'effet de l'activation mécanique des cendres volantes sur la structure et les propriétés du ciment géopolymère a été étudié. Des dispositifs de broyage à énergie élevée, à savoir broyeurs à compression et à vibration, ont été utilisés pour l'activation mécanique. On a observé un abaissement de la température de réaction de géopolymérisation dû à l'augmentation de la réactivité des cendres volantes par activation mécanique. Les produits préparés en utilisant les cendres volantes mécaniquement activées contiennent une plus grande quantité de géopolymère, ont une structure compacte et une résistance remarquablement plus élevée par rapport aux géopolymères obtenus sur les cendres non traitées. L'effet de l'activation mécanique s'avère spécifique du broyeur et, une combinaison appropriée du broyeur et de l'activateur alcalin est nécessaire pour obtenir l'effet bénéfique des propriétés mécaniques du géopolymère.

Introduction Geopolymers are amorphous to semi-crystalline materials with a three dimensional silico-aluminate network [1]. Geopolymerisation involves the chemical reactions between various alumino-silicate oxides and silicates under highly alkaline conditions, yielding polymeric Si– O–Al–O bonds [2, 3]. Fly ash generated in large quantities in coal based thermal power plants is a potential raw material for geopolymers due to the presence of silica and alumina bearing phases as major constituents. Recently, uses of fly ash in geopolymers have attracted intensive research attention [3-7]. Fly ash based geopolymeric binders have been investigated and in most cases low compressive strength are reported [3, 4]. Only small fraction of silica and alumina present on the surface of fly ash particles takes part in the geopolymerisation reaction due to its poor reactivity. The unreacted fly ash particles lead to low and inconsistent strength in the geopolymer [4]. Thus, the reactivity of fly ash is an important consideration to exploit its potential in geopolymer technology. Recently, there has been a spurt of research activities in the applications of mechanical activation of solids for development of new materials and processes [8-16]. The term mechanical activation is applied to the field of reactions/physico-chemical changes and solid reactivity induced by mechanical energy or a combination of mechanical and chemical activation [8-10]. In general, the process of activation depends on the breakage mechanism (shear, compression, impact etc) and the rate at which energy is supplied to the system [8, 9, 11, 12]. The solid

state reaction during mechanical activation are generally believed to be favoured due to increase in surface area, stress and defects induced in solid structures, phase transformations, localized and overall thermal effects, repeated welding of interfaces and fracture leading to dynamic creation of fresh surfaces for reactions etc. Mechanical activation of fly ash in high-energy mills is suggested to improve its reactivity [16]. Enhanced reactivity of fly ash by mechanical activation has been utilised in the development of improved blended cements containing higher proportion of fly ash as clinker replacement [16]. In the present work, the reactivity of the fly ash was enhanced through mechanical activation using attrition and vibratory mills. The mechanically activated fly ash was used as base material for the preparation of geopolymer cement with sodium silicate or sodium hydroxide as alkali activator. Effect of mechanical activation on the geopolymerisation of fly ash was investigated by thermal analysis. The geopolymers were characterised in terms of phases present and their microstructure. The mechanical properties of the samples were evaluated and compared with raw fly ash based geopolymer. The focus of the study is on structure and properties relationship.

Materials & M ethods Locally available Indian (ASTM class F) fly ash was used as the source material. The physicochemical properties of the fly ash are given in Table 1.

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Table 1: Physicochemical properties of fly ash

Chemical Composition (wt. %) Fe2O3 CaO MgO MnO LOI* 4.5 1.5 0.5 0.6 2 Physical Properties Phases Present Glass, Quartz, Mullite Specific gravity 2.47 * Loss on ignition SiO2 57.5

Al2O 3 27.5

A batch type attrition mill (Model: PE075, NETZSCHFeinmahltechnik GmbH, Germany) and two tube continuous type vibratory mill (Model : MC137, Sayaji, India) were used for mechanical activation. The as received fly ash was directly fed to the mill. The activation time depended on the mill operating parameters and milled product quality. The raw and activated fly ash was characterised in terms of particle size distribution and morphology by laser particle size analyser (Mastersizer, Malvern, U.K) and scanning electron microscope (840A SEM, JEOL, Japan), respectively. Analytical grade sodium hydroxide in flake form (98% purity), and sodium silicate (Modulus value 1.5, 1.75 and 2.0) were used as the alkaline activators. The alkaline activators were dissolved in water before use. Samples were prepared using raw as well as mechanically activated fly ash. The fly ash and alkaline activators were thoroughly mixed, made in desired shape by uniaxial compression, dried at ambient temperature for 6 hours and then heated at 60°C for 2 hours in a drying oven for geopolymerisation. The geopolymers obtained were tested for compressive strength. The samples were characterised in terms of their microstructure by SEM, and phases present by powder Xray diffraction (XRD) method. XRD patterns were recorded on a Siemens diffractometer (Model D500) using CoKα radiation. The dried and powdered fly ash and alkali activator mix were also analyzed by SEIKO simultaneous TG/DTA (Model No. 320, Sensitivity =1µg) from 30-180 °C.

(a)

(b)

(c) Figure 2: SEM micrographs showing morphology of particles in (a) RFA (b) AMFA and (c) VMFA

Figure 3: Compressive strength of sodium silicate based geopolymer

Results & Di scussions

Figure 1: Particle size distribution of RFA, AMFA and VMFA

Fig.1 shows typical particle size distribution of raw (RFA), attrition-milled (AMFA) and vibration-milled (VMFA) fly ash. A significant reduction in particle size is obtained in AMFA (X50 = 12 µm) and VMFA (X50 = 9 µm). Also different particle morphology was observed in milled samples when examined under SEM (Fig.2). AMFA showed mostly small size spherical particles without any aggregation whereas VMFA showed spherical to semi-angular particles with aggregation. 114

Fig.3 shows variation in compressive strength of sodium silicate based geopolymer cement using RFA, AMFA and VMFA. The compressive strength increased with the modulus value. At the modulus value of 1.5, not much difference in the compressive strength of mechanically activated and non-activated fly ash based geopolymers was found. At higher modulus values, AMFA based samples have shown the inferior strength but the VMFA based samples have shown better compressive strength. However, with the increase in modulus value, the flowability of geopolymer paste decreased. In case of sodium hydroxide based samples, a remarkable increase in strength was observed when mechanically activated fly ash was used (Fig.4). The compressive strength increased with the increase in sodium hydroxide in all the cases. The VMFA based geopolymer have shown best compressive strength values followed by AMFA and RFA based samples. Although higher concentration of sodium hydroxide improved the compressive strength of geopolymers, it was observed that part of it remain unreacted and leached out and deposited onto the surface. Since sodium hydroxide based geopolymers have shown most promising results, samples with 5% NaOH were characterized in terms of TG/DTA, XRD and SEM.


Figure 4: Compressive strength of sodium hydroxide based geopolymer

The DTA curves (Fig.5) of geopolymer cement indicate the different reaction kinetics of non-activated and mechanically activated samples. The shifting of peak towards lower temperature zone in AMFA and VMFA indicates that the geopolymeric reaction took place at somewhat lower temperatures. TG/DTA analysis was also carried out at 60°C for 2 hours. It was observed that the reaction took less time in AMFA and VMFA based geopolymers. No significant difference in XRD patterns (Fig.6) of activated and raw fly ash samples suggests that similar phases were formed in all the samples. Presence of sodalite peak indicates the geopolymerisation reaction between Na, SiO2 and Al2O3. The microstructure of the geopolymers is shown in Fig.7. The geopolymers using mechanically activated fly ash are characterized by very compact microstructure. VMFA based geopolymers have shown almost pore free and dense microstructure. In both VMFA and AMFA based geopolymers, growth of another geometric shape of crystal was observed.

Figure 6: XRD patterns of geopolymer

(a)

(b)

(c) Figure 7: SEM micrographs showing microstructure of geopolymer based on (a) RFA, (b) AMFA, and (c) VMFA

Conclusi ons

Figure 5: DTA curve of geopolymer mix

Based on the XRD results (Fig. 6) in conjunction with microstructural evidence (Fig. 7), it can be surmised that the greater strength observed in the geopolymer based on VMFA and AMFA is not directly related with the phases present, but to the formation of compact microstructure. This can be explained in terms of increased reactivity of fly ash due to mechanical activation during high-energy milling. The higher reactivity of fly ash may result due to the combined effect of particle size, surface area, state of aggregation, shape, defects etc. Due to increased reactivity, the geopolymerisation reaction between fly ash and sodium hydroxide is enhanced resulting in greater formation of the geopolymer product and a more compact microstructure that leads to improved strength.

The major conclusions of this study are: 1. Mechanical activation of fly ash favours the geopolymerisation. The reaction occurs at lower temperature and takes less time. 2. In case of sodium silicate activator, only VMFA based geopolymer shows the improved compressive strength. In case of sodium hydroxide, both AMFA and VMFA based geopolymers shows improvement in compressive strength. VMFA based geopolymers gives the best compressive strength results. 3. The improvement in compressive strength is due to formation of compact microstructure in mechanically activated fly ash based samples. 4. The process of activation is mill specific and judicious selection of activation device is necessary to exploit the beneficial effect of mechanical activation in geopolymer cement. Also a suitable combination of alkali activator and mechanical activation is necessary to obtain best results.

References 1. J. Davidovits and J. Orlinski eds., Geopolymer ’88, European Conference on Soft Mineralurgy, Université de Technologie, Compiègne, France, Vol. 1-2, 1988.

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2. J. Davidovits , Synthetic mineral polymer compound of the silicoaluminates family and preparation process. FR 2.489.291, 03/09/1980 3. A Katz, Microscopic study of alkali activated fly ash, Cem. Concr. Res., 34 (9), 1998, 197-208. 4. J. C. Swanepoel and C. A. Strydom, Utilisation of fly ash in a geopolymeric material, Applied Geochemistry, 17, 2002, 1143-1148. 5. D. Hardjito, S.E. Wallah, D.M.J. Sumajouw, and B.V. Rangan, Properties of Geopolymer Concrete with Fly Ash as Source Material: Effect of Mixture Composition, 7th CANMET/ACI International Conference on Recent Advances in Concrete Technology, May 26-29, 2004, Las Vegas, USA. 6. Palomo, M.W. Grutzeck, M.T. Blanco, Alkaliactivated fly ashes, a cement for the future, Cem. Concr. Res. 29, 1999, 1323– 1329. 7. J. G. S. van Jaarsveld, J. S. J. van Deventer and G. C. Lukey, The effect of composition and temperature on the properties of fly ash- and kaolinite-based geopolymers, Chemical Engineering Journal, 89, 1-3 , 2002, 63-73. 8. Z. Juhasz and L. Opoczky, Mechanical activation of Minerals by Grinding: Pulverizing and Morphology of Particles, Ellis Horwood Limited, NY, 1994. 9. V. V. Boldyrev, Mechanical activation of solids and its application to technology, Chemistry for Sustainable Development, 83 (11/12), 1986, 821-822. 10. F. Fernandez-Bertran Jose, Mechanochemistry : an overview, Pure Appl. Chem., 71(4), 1999, 581–586. 11. U. Steinike, and H. P. Hennig, Mechanically induced reactivity of solids, KONA Powder and Particle, 10, 1992, 15-24. 12. V. V. Boldyrev, S. V. Polov and E. L. Goldberg, Interrelation between fine grinding and mechanical activation, Int. J. Min. Process, 44-45, 1996, 181-185. 13. E.G. Avvakumov, Mechanochemical synthesis as a basis for new chemical processes, Chemistry for Sustainable Development, 2-3(1994) 475-490. 14. M. Senna, Recent development of materials design through mechanochemical route, Int. J. Inorg. Mater., 3, 2001, 509-514. 15. Rakesh Kumar, .T.C. Alex, Z.H. Khan, S.P. Mahapatra, and S.P. Mehrotra, Mechanical Activation of Bauxite - Potential and Prospects in the Bayer Process, Light Metals 2005, Halvor Kvande ed., The Minerals, Metals & Materials Society, Warrendale, 2005, 77-79. 16. Sanjay Kumar, V. Rajinikanth, T. C. Alex, B. K. Mittra, Z. H. Khan, I. B. Mishra, A. Bandopadhyay and Rakesh Kumar, Utilization of high volume of blast furnace slag and fly ash in blended cements through high energy milling-, Proc. Intl. Conf. Advances in concrete composites and structures (ICACS-2005), Allied Publishers, India, 2005, 113120.

Peer-Reviewed under Geopolymer Institute publication policy

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