Alkali activated geopolymer cement

Alkali activated geopolymer cement - Coventry University...

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Geopolymer Cement from Alkali-Activated Natural Pozzolans: Effect of Addition of Minerals D Bondar (a) , C. J. Lynsdale (b) , N. B. Milestone (c) , N. Hassani (d) A. A. Ramezanianpour (e) (a) Ph.D. candidate of University of Sheffield and P.W.U.T. Research Associate. (b) Dept. of Civil and Structural Engineering, University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK. (c) Dept. of Engineering Materials University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK. (d) Research Centre of Natural Disasters in Industry, P.W.U.T., Tehran, Iran (e) Dept. of Civil Engineering, Amir Kabir University, Tehran, Iran < dlbondar@gmail.com >, < c.lynsdale@sheffield.ac.uk >, < neil.milestone@gmail.com >, < nemathassani@yahoo.com >, < aaramce@aut.ac.ir > ABSTRACT Natural pozzolans are raw materials from geological deposits with a range of chemical compositions that when combined with suitable alkali activators can be converted to geopolymer cement for concrete production. In this paper the concept of adding mineral additives to enhance the properties of geopolymer cement is introduced. Taftan andesite, a natural Iranian pozzolan, was used to study the effect of adding mineral additives such as kaolinite, lime and other calcined pozzolans on the compressive strength of geopolymer cement under both normal and autoclave curing. Scanning electron microscopy (SEM) / energy dispersive X-ray (EDX) was used to determine the composition of the gel phase in both alkali-activated Taftan pozzolan with and without mineral additions. The work has shown that deficiencies in SiO 2 , Al 2 O 3 and CaO content in the raw natural pozzolan can be compensated for by adding mineral additives for enhanced properties. INTRODUCTION Geopolymers form by the co-polymerization of dissolved silicon and aluminium species in the presence of high pH alkali silicate solutions and can be synthesized from a wide range of aluminosilicate powders including natural pozzolans [Davidovits, 1991, 1994]. Recent work [Bondar, 2009] has shown that natural pozzolans from Iran show good potential as a source of aluminosilicate. Previous work has shown that factors such as increasing molar Si-Al ratio and %CaO have positive effects on the final compressive strength of geopolymer cement [Xu and Deventer, 2000]. The aluminosilicate used for the production of a geopolymer cement must contain Al which is readily soluble with an overall molar ratio of Al 2 O 3 :SiO 2 lying between 1:3.3 and 1:6.5 [Jaarsveld et al., 1997, Rahier et al., 1996, 1997, Hos et al., 2002]. However, these ratios are not critical and are for the most part only an indicator of approximate composition. The reason for this is that while these compositional ratios are based on chemical analysis, it is
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highly unlikely that all of the silica or alumina actually take part in the synthesis reaction [Jaarsveld and Deventer, 1996]. Often the rate of dissolution of Al from natural aluminosilicates is insufficient to produce a gel of desired composition [Xu and Deventer,
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Alkali activated geopolymer cement - Coventry University...

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