REACTION PATHWAYS IN THE ALTERATION OF VOLCANIC GLASS THROUGH INORGANIC AND MICROBIALLY-MEDIATED PROCESSES (original) (raw)
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International Journal of Applied Ceramic Technology, 2020
Geopolymers have been studied as viable alternative to traditional Portland cementbased products, given the use of industrial by-products as raw materials. This work evaluated the mechanical and microstructural properties of geopolymeric mortars produced with sodium hydroxide solution, metakaolin, silica fume, and red mud. The mixtures were produced by means of dosages with different molar ratios and curing conditions. The raw materials were characterized by granulometry, chemical, mineralogical, and thermal analysis. The characterization of mortars was performed by scanning electron microscopy (SEM) and axial compressive strength tests. The precalcination at 850°C of the red mud was sufficient to make it more reactive and suitable for use in geopolymers. Noteworthy, the best mechanical strengths of metakaolin mortars for curing at 50°C, and with the lowest SiO 2 /Al 2 O 3 ratios. In the mortars with incorporated red mud, there was a decrease of strength at thermal curing conditions and with the increase of residue content, whose microstructure indicates the formation of more pores in the geopolymer matrix. The thermal curing promoted the formation of sodalite crystals, and the significant presence of Na particles on the surface suggests that part of the added NaOH did not react with the precursors.
Composition and technological properties of geopolymers based on metakaolin and red mud
Materials and Design, 2013
New geopolymer formulations were designed by sodium silicate/NaOH activation of metakaolin, iron oxide and red mud mixtures. The effects of source materials on the microstructure and mechanical properties were studied. Each formulation induces different degree of geopolymerization reaction as reflected by the phase composition where the amorphous phase is predominant. These vestiges are related to silica provided by sodium silicate more reactive in the geopolymerization than the silica of metakaolin. Moreover, the variation in strength between the geopolymers is attributed to the same factors, with higher porosity and nonreacted phases found in the red mud based geopolymer matrix. In function of curing time, the mechanical strength increased from day 1 to 28 for the samples with a low amount of red mud. In these two cases, longer curing time improves the geopolymerization state resulting in higher compressive load. The metakaolin and metakaolin/red mud products exhibited comparable water absorption and density.
Construction and Building Materials, 2019
This paper explored reported the effect of sewage sludge ash (SSA) on the mechanical and microstructural properties of geopolymers based on metakaolin (MK) involving two different SiO2/Na2O molar ratios (0.8 and 1.6), two temperature curing conditions (25°C and 65°C) and various ages of curing (1, 3, 7, 14, 28, 90 or 180 days). The geopolymers tests were characterized performed using different techniques: as X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and compressive strength of mortars. Tests were performed for both high (65°C) and room (25°C) temperature curing conditions lasting for 1, 3, 7, 14, 28, 90 or 180 days. The geopolymeric samples were activated using sodium hydroxide and sodium silicate solutions using two different SiO2/Na2O molar ratios (0.8 and 1.6). The compressive strength tests showed that the replacement of MK by SSA in 10 wt.% when cured at 25 °C with the highest SiO2/Na2O molar ratio reaches similar compressive strengths after 14 days of curing compared to the samples with only MK, which reached a maximum compressive strength of 50.8 MPa at 180 days. The FTIR analyses carried out in the geopolymer pastes with SSA (10 wt.% of SSA and 90 wt.% of MK) showed a formation of N-AS -H gels in the samples cured at 25 °C. The microstructural studies by XRD, TGA and SEM pointed out the formation of a crystalline phase as Na P-type zeolite in MK/SSA based-geopolymer pastes cured at 65 °C, which explained the loss of compressive strength of the samples cured at high temperature. However, the SSA retarded the crystallization process in the MK basedgeopolymer.
Characterization of geopolymers prepared using powdered brick
Journal of Materials Research and Technology, 2019
Geopolymerization of waste products can contribute to the solution of current environmental issues related to depletion of natural resources. In this paper, several geopolymer mixes are prepared using waste brick in powdered form, while different alkaline activators and curing conditions are applied. Experimental results show that the reaction rate at early age decreases with the increasing silicate modulus as well as with the rise of curing temperature; the reaction is though significantly slower than, e.g., for metakaolin-based geopolymers because of the low content of amorphous phase in the brick. The most compact microstructure is observed for geopolymers with highest reaction rate at early age; with increasing silicate modulus of the activator and decreasing curing temperature the compactness gradually decreases and the specific pore volume increases. Thermal analysis shows a decreasing weight loss with increasing silicate modulus for all temperatures, while dehydration of N-AS -H and C-AS -H gels are identified as the most important factors. Dehydroxylation of muscovite is found for the mixtures cured at temperatures up to 60 • C only, and decomposition of calcium carbonate just for 20 • C curing. Most crystalline phases detected by X-ray diffraction analysis in designed geopolymers are identical to those found in the raw precursor, which indicates only a partial geopolymerization and presence of a significant amount of unreacted particles. For geopolymers cured at 60 • C and 80 • C, formation of zeolitic phases is observed. While sodalite and chabazite are found only in mixtures with higher reaction rate, gismondine appears in geopolymers with higher silicate modulus.
The present paper investigated the reactivity of volcanic ash in alkaline medium and reported the effect of synthesis conditions on microstructural and mechanical properties of volcanic ash-based geopolymers. The reactivity of volcanic ash was carried out by leaching it under different NaOH concentrations (8, 10, and 12 M) and temperatures (27, 60, and 80°C), and chemical composition of the filtrate measured by ICP-OES. The influence of silica modulus (1.4, 1.5, and 1.66) and curing temperatures (27, 60, and 80°C) on microstructural characteristics of the resulting geopolymers was assessed by Calorimetry test, XRD, FTIR, 27 Al and 29 Si MAS-NMR, TGA, and FESEM-EDX. The dissolution behavior of Si is influenced by NaOH concentration, while Al is more sensitive to temperature. The low amount of dissolved species is correlated with the low amount of heat released. XRD, FTIR, 27 Al and 29 Si MAS-NMR, and TGA have shown the evidence of changes occurred during geopolymerization of volcanic ash and the extent of reaction with varying silica modulus and curing temperature. FESEM and EDX have shown that geopolymers obtained are poly(ferrosialate-siloxo), poly(ferro-sialate-disiloxo), and poly(ferro-sialate-multisiloxo) binder types with Ca 2? , Mg 2? , and Na ? as charge-balancing cations. These structures are irrespective of silica modulus and curing temperature. The curing temperature is the main factor affecting the early compressive strength.
Mechanical properties of metakaolin-based geopolymers with molar ratios of Si/Al ≈ 2 and Na/Al ≈ 1
Journal of Materials Science, 2008
The mechanical properties of four different types of geopolymers, but of the same composition (Na/Al ≈ 1, Si/Al ≈ 2 molar ratio), made using a combination of precursors, were determined. The four types were: (i) sodium aluminate (NaAlO2/NaOH solution), Ludox (colloidal SiO2 solution) and metakaolin (MK), (SAGP), (ii) NaOH, fumed silica and MK (FSGP), (iii) Ludox, NaOH and MK (LGP) and (iv) commercial sodium silicate and MK (SGP). The highest crushing strength (CCS) value obtained was for SGP (70 MPa) and the lowest value was for SAGP (16 MPa). The highest modulus of rupture (MOR) value obtained was for LGP (9 MPa) and the lowest value was for SAGP (3 MPa). The fracture toughness (K1c) and Young’s modulus (E) showed the same trend. The effect of adding sand (40 wt%) on their mechanical properties was also determined. The K1c values increased up to 65% and E values increased up to 80% compared to samples free of sand. However, CCS and MOR values did not change much and gave mixed results. Overall, porosity is found to be the chief microstructural variable limiting the mechanical properties of the geopolymers. The properties of the geopolymers are compared with those of ordinary Portland cement.
This paper looks at the possibility of using low reactive volcanic ash for making geopolymer cement. The research is directed towards (a) alteration of the reactivity of volcanic ash by mechanical activation, and (b) use of mechanically activated volcanic ash for the synthesis of a geopolymer. The effect of mechanical activation was quite visible on particle size distribution and the degree of crystallinity. The disappearance of some anorthite peaks and appearance of quartz peaks in volcanic ashes milled for 120 min demonstrate the change in mineralogy. The appearance of an intense carbonate band with milling time could be related to sorption of atmospheric CO 2 on the grains surface during mechanical activation. The manifestation of mechanical activation of volcanic ash was prominent on (a) the reaction kinetics, (b) microstructural development, and (c) physico-mechanical properties of the geopolymer product. The rate constant and extent of geopolymerization increased with milling time but decreased with curing temperature. This decrease is in non-conformity with other alumina-silicate materials used for geopolymerization such as metakaolin and fly ash. FEG-SEM and EDAX results revealed that the geopolymer gel obtained is mixture of poly(ferro-sialate-siloxo) and poly(ferro-sialate-disiloxo)
Structure, Design and Applications of Geopolymeric Materials
2007
The term “geopolymer” was firstly applied to describe a family of alkaline aluminosilicate binders formed by the alkali activation of aluminosilicate minerals. The formation of geopolymeric materials is the result of a complicated heterogeneous chemical reaction occurring between Al-Si solid materials and strongly alkaline silicate solutions. The geopolymerization reaction is exothermic and takes place under atmospheric pressure at temperatures below 100C. Despite of the intense research on the geopolymerization of different aluminosilicate materials and the development of a wide range of geopolymeric materials, the exact mechanism that takes place during geopolymerization is not fully understood. The most proposed mechanism for geopolymerization includes the following four stages, which proceed in parallel and thus, it is impossible to be distinguished: (i) Dissolution of Si and Al from the solid aluminosilicate materials in the strongly alkaline aqueous solution. (ii) Formation of...
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007
Statistical analysis of a systematic series of geopolymers with varying alkali type (sodium and potassium) and Si/Al ratio after 7 and 28 days ageing has been used as a basis for observing the development of mechanical properties with time. Minimal change in the compressive strength of specimens was generally observed in specimens of different alkali or between 7 and 28 days of ageing. However, mixed-alkali specimens with high Si/Al ratio exhibited significant increases in strength, while pure alkali specimens displayed decreased strength. The development of Young's modulus of geopolymers between 7 and 28 days was observed to be dependent on alkali, with the Young's moduli of Na-specimens decreasing at low Si/Al ratio, but increasing at high Si/Al ratio, while K-specimens exhibited the opposite effect. Mixed-alkali specimens all exhibited nominal change in Young's moduli, without any significant effect of Si/Al ratio being observed.
Effect of Olive-Pine Bottom Ash on Properties of Geopolymers Based on Metakaolin
In this research, the feasibility of using bottom ashes generated by the combustion of biomass (olive pruning and pine pruning) as a source of aluminosilicates (OPBA) has been studied, replacing the metakaolin precursor (MK) in different proportions (0, 25, 50, 75 and 100 wt. % substitution) for the synthesis of geopolymers. As alkaline activator an 8 M NaOH solution and a Na2SiO3 have been used. The geopolymers were cured 24 hours in a climatic chamber at 60 ° C in a water-saturated atmosphere, subsequently demoulded and cured at room temperature for 28 days. The results indicated that the incorporation of OPBA waste, which have 19.7 wt. % of Ca, modifies the characteristics of the products formed after alkaline activation. In general terms, the incorporation of increasing amounts of calcium-rich ashes results in geopolymers with higher bulk density. The compressive strength increases with the addition of up to 50 wt. % of OPBA with respect to the control geopolymers, contributing ...