Search

This paper reports on the synthesis and characteristics of a novel aluminosilicate glass-based cementitious binder. We investigated the hydration kinetics, degree of reaction, and phase assemblage of the glass via XRD, DTG, ²⁷Al and ²⁹Si MAS NMR, FTIR, SEM/EDS and thermodynamic modelling. The glass exhibits hydraulic properties in which the binder developed impressive compressive strength at early age. The main hydration products are an intermixed of Na and/or Al incorporated in C–S–H gel. Hydrotalcite precipitated with slower rate and thus may generate crystallization pressure on the binder at late stage. The glass reached a high degree of hydration (ca. 73 % based on quantitative ²⁹Si NMR analysis) without using any activators or co-binding systems. Therefore, the developed glass reported herein has high potential as a new low-carbon cementitious binder since it can be synthesised from naturally occurring carbonate free silicate minerals.

Geopolymers are ceramic-like materials prepared at low temperatures by reacting natural aluminosilicates (clays) or aluminosilicate wastes (fly ash and blast furnace slag) with alkalis or acids. Like ceramics, they fracture in brittle mode, but graceful failure can be induced by fiber reinforcement. Since geopolymers are processed at low temperatures, organic reinforcing fibers can be used without thermal degradation. This chapter provides a brief description of the synthesis, structure, and properties of the aluminosilicate geopolymer matrix, and reviews the effect on the physical and mechanical properties of plant-based (cellulose) reinforcing fibers and protein-based fibers (wool). The possible degradation of the fibers by the highly alkaline geopolymer matrix is discussed, as well as the comparative benefits benefits associated with the mechanical properties of long and short fibers and woven cloth reinforcement. The literature reviewed here suggests that geopolymers produced at low temperatures (

The cement industry faces an increasing demand for new supplementary cementitious materials (SCMs) as alternative to slags and ashes, the sources of which are in continuous depletion. This study reports on the characteristics of synthetic aluminosilicate glasses derived from basalt composition (BGs) as new SCMs. The pozzolanic activity of the developed glasses as well as their influence on the hydration kinetics, microstructure, and mechanical properties of blended cements are reported. The obtained results show that pastes containing BGs demonstrated faster hydration rate and higher compressive strength compared to those containing commonly applied granulated blast furnace slag (GBFS). In addition, the developed glasses demonstrated higher pozzolanic activity than GBFS as demonstrated form the measured amount of portlandite and strength activity index. The developed glasses can be obtained from earth abundant carbon-free raw materials as it is similar in composition to basalt. Therefore, this novel approach has potential to provide low-carbon cementitious binders for the concrete industry.

The field of heterogeneous catalysis has recently become increasingly interested in the utilization of industrial wastes as inexpensive precursors for active catalysts. Here we report a facile synthesis of fly-ash-based geopolymers as new highly reactive sustainable porous aluminosilicate heterogeneous catalysts for acidic and/or redox applications. The catalytic properties of these catalysts for Friedel–Crafts benzylation reactions of benzene and other substituted aromatics were thoroughly investigated. Fly ashes were collected from various sources were investigated, and the impact of the variation of their chemical and physical properties on the resulting catalysts was studied. The catalysts demonstrated excellent catalytic reactivity superior to other commonly used aluminosilicate catalysts such as M-zeolite, mesoporous molecular sieves, mixed oxides, and ionic liquids. This study not only highlights the feasibility of synthesizing active heterogeneous catalysts with predictable features from several d...

Alternative cementitious binders, based on industrial side streams, characterized by a low carbon footprint, are profitably proposed to partially replace Portland cement. Among these alternatives, alkali-activated materials have attracted attention as a promising cementitious binder. In this paper, the chemical stability of the matrix, in fiber-reinforced slag-based alkali-activated composites, was studied, in order to assess any possible effect of the presence of the reinforcement on the chemistry of polycondensation. For this purpose, organic fiber, cellulose, and an inorganic fiber, basalt, were chosen, showing a different behavior in the alkaline media that was used to activate the slag fine powders. The novelty of the paper is the study of consolidation by means of chemical measurements, more than from the mechanical point of view. The evaluation of the chemical behavior of the starting slag in NaOH, indeed, was preparatory to the understanding of the consolidation degree in the alkali-activated composites. The reactivity of alkali-activated composites was studied in water (integrity test, normed leaching test, pH and ionic conductivity), and acids (leaching in acetic acid and HCl attack). The presence of fibers does not favor nor hinder the geopolymerization process, even if an increase in the ionic conductivity in samples containing fibers leads to the hypothesis that samples with fibers are less consolidated, or that fiber dissolution contributes to the conductivity values. The amorphous fraction was enriched in silicon after HCl attack, but the structure was not completely dissolved, and the presence of an amorphous phase is confirmed (C–S–H gel). Basalt fibers partly dissolved in the alkaline environment, leading to the formation of a C–N–A–S–H gel surrounding the fibers. In contrast, cellulose fiber remained stable in both acidic and alkaline conditions.

This paper reports the synthesis of hierarchical aluminosilicate inorganic polymers (also known as geopolymers) containing both Bronsted and Lewis acid sites that function as a new class of heterogeneous solid acid catalysts. The geopolymers were synthesised from a naturally occurring clay mineral by an energy-efficiently and ecologically friendly process. Their catalytic performance was evaluated in a model liquid phase Friedel-Crafts alkylation of relatively large substituted benzenes (alkylation of toluene, anisole, p -xylene and mesitylene with benzyl chloride). The influence of the geopolymer starting composition on the acidity and porosity of the synthesised catalysts was studied and the impact of post-synthetic demetallation on their catalytic performance was investigated. The geopolymer-based catalysts achieved high catalytic activity which was superior to H Y zeolite under identical reaction conditions. These results suggest that geopolymers have considerable potential as cost efficient, readily synthesised and environmentally friendly heterogeneous solid catalysts for fine chemical applications.

Aluminosilicate inorganic polymers (geopolymers) were developed as a new class of cost-efficient, environmentally friendly, solid acid catalysts and their performance evaluated in a model liquid-phase Beckmann rearrangement reaction (cyclohexanone oxime to e-caprolactam). The active sites were generated within the structure of the geopolymers by ion-exchange with NH 4 + followed by thermal treatment. The effect of varying the starting composition on the textural and acidic properties of the geopolymer catalysts was studied and its influence on the catalytic activity was investigated. Catalytic performance was significantly improved by the use of post-synthetic treatments. No significant decrease in the yield of e-caprolactam after recycling for five times suggesting that geopolymer-based catalysts are advantageous over supported catalysts which often lose their catalytic activity due to leaching of the active sites from the support. The catalytic activities obtained in this study are comparable, and sometimes superior, to other solid catalysts suggesting that geopolymers have a great potential as environmentally benign heterogeneous catalysts.

Aluminosilicate inorganic polymers (geopolymers) can be cheaply and readily prepared from dehydroxylated kaolinite clay and have been successfully demonstrated as a new type of stationary phase in the chromatographic separation of a mixture of three model aromatic compounds (a trisubstituted benzene, an ester and a pyrrole). Grinding and sieving to 105 μm produced powders with a similar particle size distribution and morphology to standard chromatographic silica, although smaller particle sizes and other morphologies can readily be produced. Three compositions of geopolymers were studied here and their performance was compared with conventional chromatography column packing media typically used for simple open-column and flash separations (silica and aluminas). Although the geopolymers were prepared under highly alkaline conditions, washing with acid to bring them to neutral pH before use was found to be unnecessary. The results obtained with the as-prepared geopolymer of standard composition showed it to possess a significantly greater number of plates/meter than any of the other column materials, including acidic and neutral aluminas and silica, and although more of the ester adsorbed to this column than on silica, in all other important respects the behavior of the geopolymer was comparable to silica and alumina. All the geopolymers were shown to be chemically stable to strong solvents such as ethanol, by comparison with conventional media such as silica and alumina, which were decomposed by ethanol; this suggests that unlike conventional silica, the geopolymer media may be cleaned with a strong solvent between runs without being degraded, and re-used. These results indicate that geopolymers represent a promising substitute for the commonly-used silica or alumina chromatography stationary phases, being simpler and cheaper to produce, more stable to strong solvents and showing comparable or better separation characteristics.

This study reports the synthesis and mechanical properties of new inorganic polymer (geopolymer) composites unidirectionally reinforced with 4–10 vol.% natural cellulose-based fibres (NZ flax, phormium tenax). The geopolymer matrix was derived from dehydroxylated kaolinite-type clay. The mechanical properties of the fibre-reinforced composites improve with increasing fibre content, achieving ultimate flexural strengths of about 70 MPa at 10 vol.% fibre content. This represents a significant improvement on the flexural strength of the unreinforced geopolymer matrix (about 5.8 MPa), and all the composites show graceful failure, unlike the brittle failure of the matrix. Scanning electron microscopy was used to study the morphology of the fibre-matrix regions and a combination of thermogravimetric analysis (TGA) and thermal shrinkage measurements of these composites suggests that despite the formation of microcracks due to water loss from the geopolymer matrix, the fibres are thermally protected by the matrix up to 400 °C. The flax fibres do not appear to be compromised by the alkaline environment of the matrix, suggesting new possible applications for these low-cost simply prepared construction materials.

New fibre-reinforced composites of aluminosilicate inorganic polymer (geopolymer) with natural protein-based fibres (carpet and Merino wool) were developed, and their mechanical properties determined. The surfaces of some of the wool fibres used in this study were chemically modified to improve their alkali resistance and reinforcing properties. The flexural strengths and failure characteristics of the composites, determined on bar-shaped samples by a three-point test method, show an approximately 40 % improvement over the unreinforced matrix and graceful failure, unlike the unreinforced matrix that displays ceramic-like brittle fracture. Interaction between the sulphide linkages of the wool and the aluminosilicate matrix produces a blue-green colour in the wool, shown by UV–visible and IR spectroscopy to be related to the formation of the sulpho-aluminosilicate compound sodalite. The thermal behaviour of these composites was studied by thermogravimetric analysis, and scanning electron microscopy was used to study the fibre-matrix interface.