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XRD analysis of white kaolin and iron-rich lithomarge. K=kaolinite, M=magnetite, Go=goethite, A=anatase.
Source publication
Geopolymer binders have emerged as an alternative to Portland Cement systems for specialist applications due to their improved durability and environmental impact. Geopolymer binders can be made by combining alkali activators with precursor materials including high purity dehydroxylated kaolin (metakaolin) or pulverised fuel ash. Although the techn...
Contexts in source publication
Context 1
... kaolin was analysed by XRD and results confirm it to be composed of kaolinite and anatase ( Figure 1). 'High- purity' kaolin typically implies approximately 99% kaolinite, thus the anatase is only present in trace amounts. ...
Context 2
... as mentioned, 'high-purity' typically implies approximately 99% kaolinite. The iron-rich lithomarge from Co. Antrim was analysed in its raw form to enable semi-quantitative analysis to be carried out prior to dehydroxylation of the kaolinite (Figure 1). XRD highscore analysis indicates that the material is composed of 70.1% kaolinite, 24.3% goethite, 3.6% anatase and 2.1% magnetite. ...
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Citations
... Lecomte-nana et al. [30] showed that the dissolution of iron minerals from raw laterite in fulvic acid led to the development of a hydrated iron-rich binder phase, contributing to the strength development of the material. Although some studies have investigated the role of Fe in both clay-based [32,33] and red mud-based binders [34] the behavior of iron minerals in these binder phases, and the role of iron throughout the reaction processes, has not yet been investigated in detail for alkali-and acidic-activated materials. ...
In this work, two different laterites (iron contents of 13.07 and 49.34 wt%, respectively, for lateritic clay, LAC, and iron-rich laterite, LAI) were selected and calcined at 600 °C. The obtained calcined laterites, namely LAI600 and LAC600, were separately mixed with an alkaline solution (silicate modulus of 1.35) or an acidic solution (phosphoric acid solution at pH ≤ 2) for the synthesis of inorganic polymer products. The fabricated products were cured at 20 °C (ambient) and 40 °C (oven). The obtained results showed that the compressive strength of each series of alkaline-based inorganic polymer binder increased with ageing time (7 and 28 days) for room temperature curing, while the reverse trend was noted for oven-cured specimens. The best mechanical performance was obtained when using a phosphoric acid solution, 38 and 52 ± 1 MPa; 62 and 65 ± 1 MPa at 28 days for LAC and LAI respectively. It appeared that a higher iron content within the laterite contributed to an increase in the compressive strength under acidic conditions (LAI (59 MPa) > LAC (48 MPa)) compared to the behaviour obtained under alkaline conditions (LAI (6 MPa) < LAC (29 MPa)). Accordingly, the acidic products exhibited a dense structure (with lower porosity) and contained amorphous iron/aluminium phosphate phases such as berlinite (FePO4), iron hydrogen phosphate hydrate (Fe3H15(PO4)8·4H2O), ferrowyllieite (AlFe2Na2(PO4)3) and sodium iron phosphate (Na3Fe2(PO4)3) arising from the alteration of iron minerals in an acidic medium, confirmed by Mössbauer spectroscopy and electron paramagnetic resonance spectroscopy.
... Lecomte-nana et al. [30] showed that the dissolution of iron minerals from raw laterite in fulvic acid led to the development of a hydrated iron-rich binder phase, contributing to the strength development of the material. Although some studies have investigated the role of Fe in both clay-based [32,33] and red mud-based binders [34] the behavior of iron minerals in these binder phases, and the role of iron throughout the reaction processes, has not yet been investigated in detail for alkali-and acidic-activated materials. ...
In this work, two different laterites (iron contents of 13.07 and 49.34 wt%, respectively, for lateritic clay, LAC, and iron-rich laterite, LAI) were selected and calcined at 600 °C. The obtained calcined laterites, namely LAI600 and LAC600, were separately mixed with an alkaline solution (silicate modulus of 1.35) or an acidic solution (phosphoric acid solution at pH ≤ 2) for the synthesis of inorganic polymer products. The fabricated products were cured at 20 °C (ambient) and 40 °C (oven). The obtained results showed that the compressive strength of each series of alkaline-based inorganic polymer binder increased with ageing time (7 and 28 days) for room temperature curing, while the reverse trend was noted for oven-cured specimens. The best mechanical performance was obtained when using a phosphoric acid solution, 38 and 52 ± 1 MPa; 62 and 65 ± 1 MPa at 28 days for LAC and LAI respectively. It appeared that a higher iron content within the laterite contributed to an increase in the compressive strength under acidic conditions (LAI (59 MPa) > LAC (48 MPa)) compared to the behavior obtained under alkaline conditions (LAI (6 MPa) < LAC (29 MPa)). Accordingly, the acidic products exhibited a dense structure (with lower porosity) and contained amorphous iron/aluminium phosphate phases such as berlinite (FePO4), iron hydrogen phosphate hydrate (Fe3H15(PO4)8·4H2O), ferrowyllieite (AlFe2Na2(PO4)3) and sodium iron phosphate (Na3Fe2(PO4)3) arising from the alteration of iron minerals in an acidic medium, confirmed by Mössbauer spectroscopy and electron paramagnetic resonance spectroscopy.
... It has been identified that calcined clays offer probably the greatest scope among all materials to be used on a gigatonne per annum scale in place of Portland cement [24]; their incorporation into blends with Portland cement is certainly a key avenue by which these materials will add value in the global built environment, but the production of alkali-activated clay-based cements is certainly of strong technological and societal interest in areas where the necessary resources are available [25]. Significant commercial advances have recently been made in this regard in the UK [26,27] and elsewhere, but there is a clear need for further advancement in both the design and testing of clay-based alkali-activated binders to enable scale-up and deployment to continue at pace, to exercise the full potential of these materials. This will also feed into ongoing standardisation efforts (e.g. ...
The combination of a calcined clay with an alkali silicate or hydroxide solution has been identified since the 1920s to yield potentially useful materials. More recently these have become termed ‘geopolymers’, and have been popularised under that name. This paper briefly summarises some of the earlier history of alkali-calcined clay binders and related materials including synthetic zeolites, exploring some of the reasons underlying the more recent broadening of interest in this research field, and identifying some of the future opportunities that arise through the use of these materials. These cements may particularly be capable of offering very good technical performance and cost-effectiveness in a variety of applications, with an environmental emissions footprint lower than that of competing materials.
... It has been identified that calcined clays offer probably the greatest scope among all materials to be used on a gigatonne per annum scale in place of Portland cement [24]; their incorporation into blends with Portland cement is certainly a key avenue by which these materials will add value in the global built environment, but the production of alkali-activated clay-based cements is certainly of strong technological and societal interest in areas where the necessary resources are available [25]. Significant commercial advances have recently been made in this regard in the UK [26,27] and elsewhere, but there is a clear need for further advancement in both the design and testing of clay-based alkali-activated binders to enable scale-up and deployment to continue at pace, to exercise the full potential of these materials. This will also feed into ongoing standardisation efforts (e.g. ...
The global abundance of low purity kaolin clay and the low embodied energy associated with its calcination makes it a promising aluminosilicate source that will extend the application of geopolymers. In this paper, the compressive strength and microstructure of iron rich, calcined clay based geopolymer mortars activated by two forms of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) solutions were studied and reported. The samples were cured either in the air or under sealed conditions. The result shows that the 28 days strength of the mortars achieved by reacting the calcined clay with hydrous sodium silicate powder, dissolved under normal atmospheric conditions and sodium silicate solution produced in a pressure reactor vessel are 0.5 MPa and 28.8 MPa respectively. The former produced a non-geopolymer mortar that has a discrete, undensified and uncompacted structure with heavy presence of residual particles, thus, achieving a strength that is 1.7% of the latter. The functional group analysis reveals that the binding phase of the peak strength mortar is ferro sialate (Fe-Si-O-Al).
