Influence of the Nature and Rate of Alkaline Activator on the Physicochemical Properties of Fly Ash‐Based Geopolymers

Alouani, Marouane El; Alehyen, Saliha; Achouri, Mohammed El; Hajjaji, Abdelowahed; Ennawaoui, Chouaib; Taïbi, M.

doi:10.1155/2020/8880906

Cited by 23 publications

(23 citation statements)

References 56 publications

(47 reference statements)

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“…The size of metal cation K+ (1.33 Å) is larger than that of Na+ ion (0.97 Å) which results in formation of compact structure in the geopolymer matrix. On the chemical side, the cation K + should be associated with more water molecules than the cation Na + which results in an increase in the condensation step in the geopolymerization reaction during the formation of amorphous alumina-silicate structures [ 29 , 30 , 31 ].…”

Section: Resultsmentioning

confidence: 99%

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Strength and Microstructure Characteristics of Blended Fly Ash and Ground Granulated Blast Furnace Slag Geopolymer Mortars with Na and K Silicate Solution

2021

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Mineral geopolymer binders can be an attractive and more sustainable alternative to traditional Portland cement materials for special applications. In geopolymer technology the precursor is a source of silicon and aluminium oxides, the second component is an alkaline solution. In the synthesis of geopolymer binders the most commonly used alkaline solution is a mixture of sodium or potassium water glass with sodium or potassium hydroxide or silicate solution with a low molar ratio, which is more convenient and much safer in use. In this paper, we present the influence of sodium or potassium silicate solution on the physical and mechanical properties of fly ash and ground granulated blast furnace slag-based geopolymer mortars. Mercury intrusion porosimetry and microstructural observation allowed for comparing the structure of materials with a different type of alkaline solution. The evolution of compressive and flexural tensile strength with time determined for composites using 10%, 30% and 50% slag contents (referring to fly ash mass) was analysed. The tests were performed after 3, 7, 14 and 28 days. It was observed that, as the amount of slag used increases in the precursor, the strength of the material grows. Mortars with the sodium alkaline solution were characterised by a higher strength at a young age. However, the values of strength 28 days were higher for geopolymers with potassium alkaline solution reaching 75 MPa in compression. Geopolymer mortar microstructure observation indicates a high matrix heterogeneity with numerous microcracks. Matrix defects may be caused by the rapid kinetics of the material binding reaction or shrinkage associated with the drying of the material.

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Section: Resultsmentioning

confidence: 99%

“…After an extended period of time, the effect of the particle size begins to change. Larger potassium cations allow to form a stronger mineral matrix [ 29 ].…”

Section: Resultsmentioning

confidence: 99%

Strength and Microstructure Characteristics of Blended Fly Ash and Ground Granulated Blast Furnace Slag Geopolymer Mortars with Na and K Silicate Solution

2021

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“…Thus, the differences in metal losses shown in Figure 4 are unrelated to solvent saturation. Instead, it could be related to the strength of Na and K bonds formed during the geopolymerization process 19–21 or to the solvent accessibility to the porous network to leach out the cations. Nevertheless, such losses do not seem to have significantly affected the transesterification performance, as reported in our previous work 10 …”

Section: Resultsmentioning

confidence: 99%

Leachability and basicity of Na‐ and K‐based geopolymer powders and lattices used as biodiesel catalysts

Botti

Innocentini

Faleiros

et al. 2021

Int J Applied Ceramic Tech

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Geopolymer powders and 3D‐printed lattices have shown promising preliminary results as heterogeneous catalysts for the transesterification of vegetable oils to produce biodiesel. However, questions about the basicity of catalytic sites and the leaching characteristics of metals (K, Na) and hydroxyl groups in the reactional mixtures remained. The leaching of alkaline ions in methanol and biodiesel for powder and printed geopolymer formulations based on K, Na, or Na+K activators and treated at 110 to 700°C was investigated, as well as the physiochemical modifications of the materials. The Hammett indicators were used to determine base strength, and both leachable and total basicities were quantified. The amount of Na and K leached into the biodiesel phase was negligible (<1% wt.%). Methanol leaching reached a maximum of 29.3%. The base strength ranged between 11.0 and 18.4. Potassium‐based geopolymer lattices presented the highest basicity, followed by sodium and sodium‐potassium geopolymer catalysts. The basicity of all formulations decreased gradually as the calcination temperature increased. When compared to the homogeneous catalysts NaOH and KOH, the level of biodiesel contamination with Na and K is 81–93% lower. The findings support the heterogeneous nature of geopolymers as biodiesel catalysts and further validates their use for this application.

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“…The highest compressive strength was in the 80%:20% P/A group with a 2:1 variation of SS/SH. The alkaline activator with high silicate content can accelerate the geopolymerization process so that it also increases the compressive strength of geopolymer binders [31,36,[52][53][54]. The average percentage increase was 18% in each group.…”

Section: Sodium Silicate To Sodium Hydroxide Ratiomentioning

confidence: 94%

Mechanical Properties and Microstructure of Geopolymer Binder Based on Umeanyar Slatestone Powder

Astariani¹,

Salain²,

Sutarja³

et al. 2021

cea

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This research focuses on the mechanical and microstructure properties of geopolymer binder with slatestone waste as the base material. This geopolymer binder comes from industrial waste crushing slate in the Umeanyar area. This waste is processed into stone powder (USSP) which contains SiO 2 (49%), Al 2 O3 (11%), CaO (11.2%). This USSP uses a sodium hydroxide (SS) activator with a concentration of 14 M. The proportion of the mixture of precursor and activator (P/A) is 70%: 30%; 75%: 25%; 80%: 20% and alkaline activator Na 2 SiO 3 : NaOH (SS/SH) of 1:1; 1.5:1; 2:1, by weight. Samples of specimens were made in the form of a cube with a side of 50 mm and tested at the age of 7 and 28 days. Mechanical properties tested include density and compressive strength based on ASTM-C39. Meanwhile, the microstructural analysis used X-Ray Diffraction (XRD) and Scanning Electronic Microscope-Energy Dispersive X-Ray (SEM-EDX) analysis. The results of the density test were 1.90g/cm 3 and 1.85g/cm 3 respectively and the compressive strength test results were 7.40 MPa and 12.73 MPa at the age of 7 and 28 days, respectively.

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Influence of the Nature and Rate of Alkaline Activator on the Physicochemical Properties of Fly Ash‐Based Geopolymers

Cited by 23 publications

References 56 publications

Strength and Microstructure Characteristics of Blended Fly Ash and Ground Granulated Blast Furnace Slag Geopolymer Mortars with Na and K Silicate Solution

Strength and Microstructure Characteristics of Blended Fly Ash and Ground Granulated Blast Furnace Slag Geopolymer Mortars with Na and K Silicate Solution

Leachability and basicity of Na‐ and K‐based geopolymer powders and lattices used as biodiesel catalysts

Mechanical Properties and Microstructure of Geopolymer Binder Based on Umeanyar Slatestone Powder

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