Development of geopolymers supported by system analysis.

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1 M. Weil, A. Buchwald, K. Dombrowski: Development of geopolymers supported by system analysis. Proceedings of the 2nd Int. Symposium of Non-Traditional Cement and Concrete, ed. by Bilek and Kersner. (2005) 25-31ISBN:

2 Development of Geopolymers Supported by Systems Analysis M. Weil, K. Dombrowski, A. Buchwald Abstract Up to now, economic and ecological assessments have been carried out mainly after the development of materials. At that point of time, however, there is only a small degree of freedom to change the composition or process and to optimize the materials. The present paper shall focus on a new approach to materials development, illustrated by the example of geopolymers. In this approach, systems analysis shall accompany process and material development at an early stage, the aim being to guide the development in a sustainable way. Keywords System analyses, economic aspects, ecological aspects, material development, LCA, LCC, MCDA, geopolymers, alkali-activated materials, evaluation of raw materials 1 Background Geopolymer Geopolymers consist of a silicate-aluminate solid component (reactive material) and an alkaline liquid component (activator agent). After simple mixing of both components, dissolution takes place, accompanied and followed by a polycondensation [Davidovits 1976]. The formed polymeric network of alumosilicates (geopolymer binder) hardens in an X-ray amorphous structure. Depending on the amount of soluble calcium oxide in the raw materials, also mineral phases may occur, similar to the hydration products of portland cement [Buchwald et al. 2005a]. Geopolymers have been investigated for more than 25 years. Despite these long-lasting and continuous investigations, geopolymers have not yet reached a wide application. In fact, a wide range of applications is described in literature, but only a few niche applications can be found on the market. This is surprising, especially because geopolymers (in comparison to cement-based composite materials or ceramics) are reported to have many advantages: Resistance against acids Temperature resistance High strength 1/7

3 High durability Cold setting Quick setting Stable bonding of heavy metals and harmful substances Simple manufacturing technique The favorable technical properties are proved by numerous investigations, e.g. [Bakharev 2005], [Fernandez-J. & Palomo 2003], [Bakharev & Sanjayan 2002], [Hermann et al. 1999]. But they depend on curing time and temperature and very strongly on the mixture composition of the chosen solid and liquid components. Ecological and economic features of geopolymers have hardly been investigated so far. 1 But it can be assumed that they depend very strongly on the mixture composition, too. So far, metakaolin has been applied mainly as a solid component to produce highperformance geopolymers. However, heated kaolin (metakaolin) is a relatively expensive raw material. Consequently, the application fields are restricted due to the costs. In contrast to this, relatively cheap industrial by-products or residues, such as blast furnace slag, fly ashes or sewage sludge ashes, can also be used as solid components. These activated solids, however, may be associated with some drawbacks regarding the performance, e.g. retarded setting or low strength. Furthermore, the geopolymer system is very sensitive to changes of the chemical composition of the secondary raw materials, which is why the properties of such geopolymers vary. 2 Hence, the application fields are restricted by the performance. Having this background, the question arises how geopolymers should be developed taking into account their properties, costs, and also the overall goal of minimizing the environmental impact? 2 Goal and Benefit of the Approach The overall goal of this project is the selection and optimization of the most promising geopolymer compositions for specific fields of application. The authors will present a methodological approach to integrating technical, economic, and ecological aspects in the early stages of material development. 1 2 For geopolymers in general, there is no reliable information available about their environmental impact. Available are only rough estimations of the environmental advantages (energy consumption and greenhouse gases) of geopolymeric binders in comparison to cement binders [Davidovits 2002], [Davidovits & Davidovits]. These estimations do not consider the use or after-use phase of geopolymers. In fact, the geopolymer system is sensitive to all changes of the composition of all raw materials, but chemical variations of secondary resources in general are higher than those of primary raw materials. 2/7

4 In the normal case of material development, economic and ecological assessment is carried out after the technical investigations are finished (T M, Figure 1) or they are postponed to the subsequent phase of product development (T M -T P, Figure 1). At this time, the availability of information is relatively high to carry out an economic and ecologic assessment, but the degree of freedom is quite small to change the manufacturing process or composition of a material. This means that changes in this stage are associated with new additional investigations of materials and additional costs. These disadvantages shall be prevented by the approach presented here considering economic and ecological aspects in the early stages of material development already. The challenge will be to deal with the relatively low level of information and to nevertheless ensure a favorable development of materials for selected fields of application. Information Degree of freedom Early stage T M T P Product Material development Product development Figure 1: Level of information and degree of freedom during material and product development 3 Approach It is started from a broad variety of raw materials, which will be reduced step by step to a few promising material combinations (geopolymeric product) for specific applications (Figure 2). 3/7

5 3 rd Step: Detailed LCA, LCC and optimization of most promising geopolymers 2 nd Step: Streamlined LCA, LCC and key properties 1 st Step: Screening of mineral raw materials Development of geopolymers for specific applications Figure 2: Development of geopolymers for specific applications. The approach comprises three steps of investigation The approach is generally divided into three single steps (Figure 2): First step The first step is characterized by a screening of the solid raw materials. To rank the different raw materials, a Multi Criteria Decision Analysis (MCDA) is conducted, which considers all the subcriteria of the category groups of technique, economy, and ecology/health. The results are used to identify the most promising raw materials for certain application fields. Less promising raw materials will be excluded from further investigations. Second step In second step the key properties (e.g. acid resistance) of material combinations are investigated. This technical investigation is accompanied by streamlined Life Cycle Assessment (LCA) and Life Cycle Costing (LCC). The results are used to identify the most promising material combinations for specific application fields. In this stage, the geopolymer material combination will be compared with existing products in the respective field of application to also obtain further information for the optimization process during the third step. The less promising geopolymer material combination will be excluded from the further investigations. Third step The third step is characterized by the optimization of the most promising geopolymer material combination for a set of specific applications. A detailed LCA and LCC regarding a specific application will be made for both geopolymeric and existing products. The results will reveal not only proven profiles of properties (technical, economic, ecological), but also indicate in which applications geopolymers possess a competitive position. 4/7

6 3.1 First Step This section shall deal with the first step exclusively. The detailed methodological description of all steps of the approach will be published elsewhere [Weil et al. 2005]. The goal of the first step is the evaluation and ranking of different raw materials for certain fields of application. Three criteria with several subcriteria (indicators) will be considered: 1. Technique - reactivity - mechanical strength - resistance against acids - temperature resistance - fast setting - workability 2. Ecology/Health - availability/consumption of mineral resources - consumption of energy resources - toxic load - health and safety at the workplace 3. Costs - raw material costs - costs for the thermal activation of raw materials - costs for grinding raw materials - follow-up costs caused by slow setting - follow-up costs caused by high water sorption The different quantitative and qualitative indicator values are comparable and countable due to a transformation into values between 0 (bad) and 1 (very good), cf. [Buchwald et al. 2005b]. A ranking of the different raw materials was carried out to select the more promising ones and to accordingly exclude the less promising ones from the further investigations. The ranking was made for all application fields considered. A two-stage process was used. Stage 1(ranking with respect to technical aspects): The authors define the weightings of the different technique indicators (subcriteria) with respect to the specifications of the application field. This has to be done for all application fields considered. By calculating all different raw material alternatives with the different set of weightings, a ranking order of all raw materials is obtained for each application field. The less promising alternatives (with low values) are excluded from the next ranking step. 5/7

7 Stage 2 (ranking with respect to technical, economic, and ecological aspects): After the first stage, the alternatives remaining in each application field are ranked with respect to technical, economic, and ecological aspects. The result of a new calculation is a new ranking order of the raw materials. Again, the less promising materials in each application field are excluded from the further investigations. After this, the promising raw materials can be used in step two to develop and optimize raw material combinations for specific application fields. The preliminary results of this first step are published in [Buchwald et al. 2005b] and [Weil et al. 2005]. 4 Conclusions The sustainable development of materials with enhanced properties, but also with economic and ecologic advantages is one of the challenges of modern materials science. In practice, economic and ecological aspects are considered rarely, which is probably due to the low level of information available in the early phase of material development. Based on the example of geopolymers, a new methodological approach is presented for the development of materials with favorable properties with respect to technical, economic, and ecological aspects. Acknowledgements This paper was elaborated with the financial support of the VolkswagenStiftung, Germany. Reference [Bakharev 2005] [Buchwald et al. 2005a] [Buchwald et al. 2005b] T. Bakharev: Resistance of geopolymer materials to acid attack. Cement and Concrete Research, Volume 35, Issue 4, April 2005, Pages A. Buchwald, K. Dombrowski, M. Weil (2005): The influence of calcium content on the performance of geopolymeric binder especially the resistance against acids. Geopolymer Conference 2005, Saint-Quentin, France A. Buchwald, K. Dombrowski, M. Weil (2005): Evaluation of primary and secondary materials under technical, ecological and economic aspects for the use as raw materials in geopolymeric binders. 2nd International Symposium. Non- Traditional Cement & Concrete, Brno, Czech Republic 6/7

8 [Davidovits & Davidovits] [Davidovits 1976] [Davidovits 2002] [Fernandez-J. & Palomo 2003] [Bakharev & Sanjayan 2002] J. Davidovits, F. Davidovits: Up to 80% reduction of CO2 greenhouse gas emission during cement manufacturing. J. Davidovits: Solid-phase synthesis of a mineral block polymer by low temperature polycondensation of aluminosilicate polymers. I.U.P.A.C. International Symposium on Macromolecules, Stockholm; Sept. 1976; Topic III, New Polymers of high stability J. Davidovits: Environmental Drivers. International Conference Proceedings of Geopolymer Melbourne, Australia, 2002 A. Fernandez-Jimenez, A. Palomo: Alkali Activated Fly Ashes: Properties and Characteristics. Proceedings of 11th International Congress on the Chemistry of Cement (ICCC), 2003 Durban, South Africa. (2003) T. Bakharev, J.G. Sanjayan: Alkali-activated slag concrete: Durability in aggressive environment. Geopolymer 2002, Melbourne, Australia [Hermann et al. 1999] E. Hermann, C. Kunze, R. Gatzweiler, G. Kiesslig, J. Davidovits: Solidification of various radioactive residues by geopolymer with special emphasis ob long-term-stability. Geopolymer 1999, Saint-Quentin, France [Weil et al. 2005] M. Weil, E. Gasafi, A. Buchwald, K. Dombrowski: Sustainable Design of Geopolymers - Integration of economic and environmental aspects in the early stages of material development. 11th Annual International Sustainable Development Research Conference, 06/2005, Helsinki, Finland Marcel Weil, Dr.-Ing., Forschungszentrum Karlsruhe; Department of Technology-Induced Material Flow (ITC-ZTS); P.O. Box 3640, Karlsruhe, Germany, phone: , fax: , marcel.weil@itc-zts.fzk.de Katja Dombrowski, Dr.-Ing., Freiberg University of Mining and Technology; Institute of Ceramic, Glass and Construction Materials, Agricolastraße 17, Freiberg, Germany, phone: , fax: , katja.dombrowski@ikgb.tu-freiberg.de Anja Buchwald, Dr.-Ing., Bauhaus University Weimar, Chair of building chemistry, Coudraystraße 13C, Weimar, Germany, phone: , fax: , anja.buchwald@bauing.uni-weimar.de 7/7

Study of the Strength Geopolymer Concrete with Alkaline Solution of Varying Molarity

IOSR Journal of Engineering (IOSRJEN) ISSN (e): 2250-3021, ISSN (p): 2278-8719 Vol. 04, Issue 06 (June. 2014), V1 PP 19-24 www.iosrjen.org Study of the Strength Geopolymer Concrete with Alkaline Solution