Nanostructural characterization of geopolymers by advanced beamline techniques

Abstract

This paper presents the outcomes of a series of beamline-based studies, the results of which are combined to provide a more detailed multiscale understanding of the structure and chemistry of geopolymer binders.The range of beamline-based characterization techniques which have been applied to the study of geopolymer binders is increasing rapidly; although no single technique can provide a holistic view of binder structure across all the length scales which are of importance in determining strength development and durability, the synergy achievable through the combination of multiple beamline techniques is leading to rapid advances in knowledge in this area. Studies based around beamline infrared and X-ray fluorescence microscopy, in-situ and ex-situ neutron pair distribution function analysis, and nano-and micro-tomography, are combined to provide an understanding of geopolymer gel chemistry, nano-and microstructure in two and three dimensions, and the influences of seeded nucleation and precursor chemistry in these key areas.The application of advanced characterization methods in recent years has brought the understanding of geopolymer chemistry from a point, not more than a decade ago, when the 1 //dx.doi.org/10.1016/j.cemconcomp.2012.07.003 analysis of the detailed chemistry of the aluminosilicate binder gel was considered intractable due to its disordered ("X-ray amorphous") nature, to the present day where the influence of key compositional parameters on nanostructure is well understood, and both gel structure and reaction kinetics can be manipulated through methods including seeding, temperature variation, and careful mix design. Preprint version of accepted article. Please cite as: J.L. Provis et al., "Nanostructural characterization of geopolymers by advanced beamline techniques", Cement and Concrete Composites 2013, 36(1):56-64. Official journal version is online at http:This paper therefore provides a review outlining the value of nanotechnology -and particularly nanostructural characterization -in the development and optimization of a new class of environmentally beneficial cements and concretes. Key engineering parameters, in particularly strength development and permeability, are determined at a nanostructural level, and so it is essential that gel structures can be analyzed and manipulated at this level; beamline-based characterization techniques are critical in providing the ability to achieve this goal.

High‐Resolution X‐ray Diffraction and Fluorescence Microscopy Characterization of Alkali‐Activated Slag‐Metakaolin Binders

“…The formation of different C–A–S–H type gels can be identified, and they are labeled in the micrographs as “inner” and “outer” product gels, following previous work in alkali‐activated slag systems which identified these two types of product using SEM, TEM, X‐ray tomography, and other techniques . The inner gel is enriched in Ca over Al and Si, when compared with the outer product gel, as seen clearly in the normalized intensity results in Fig.…”

“…High‐resolution X‐ray fluorescence microscopy has previously been applied to obtain information regarding elemental distributions in portland cement–based materials, and alkali‐activated systems based on fly ash, with only a very few analysis of slag/metakaolin blends available in the literature . The use of a tightly focused X‐ray beam enables extremely high‐resolution analysis of elemental compositions within the binder structure, whereas similar analysis by scanning electron microscopy is limited by the large interaction volumes observed when high‐energy electron beams interact with low‐elemental number solids, and lower chemical sensitivity .…”

Recycled natural wastes in metakaolin based porous geopolymers for insulating applications

“…It is suggested that the difference in dissolution of the two wastes created a difference in the polymerization after the action of the blowing agent. As already indicated by Provis et al [27], the final product of geopolymerization will present a different microstructure and crystallinity at nanostructure level with the different levels of soluble silica. The colloidal phase from amorphous silica permitted to harmonize the distribution of gas from the aluminum powder.…”

“…Geopolymer is a wide range of alkaline-or alkali-silicate-activated aluminosilicate binders of chemical formulae M 2 O Á mAl 2 O 3 Á nSiO 2 with m $ 1 and 2 rn r6, and where M represents one or more alkali metals [27]. Our hypothesis of the partial substitution of metakaolin with rice husk or volcanic ashes has immediate effects on improving the Si/Al ratio of the solid precursors.…”

Recent studies of cements and concretes by synchrotron radiation crystallographic and cognate methods

“…mainly focused on their own activities covering some techniques: (i) full-field soft X-ray nanotomography; (ii) scanning transmission X-ray microscopy; (iii) scanning X-ray microdiffraction microscopy; and (iv) high pressure X-ray powder diffraction. On the other hand, Prof. Provis's group has also reported one review, [17] mainly focused on their own activities arising from BL-based studies (synchrotron and neutron), dealing with the multiscale understanding of the microstructure and chemistry of geopolymer binders. In this case, the reviewed synchrotron techniques were: (i) scanning infrared spectro-microscopy; (ii) scanning fluorescence X-ray microscopy; and (iii) X-ray nano-and micro-tomographies.…”