Dissolution mechanism of fly ash to quantify the reactive aluminosilicates in geopolymerisation

Abstract

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Recycling and Application of Mine Tailings in Alkali-Activated Cements and Mortars—Strength Development and Environmental Assessment

“…The amorphous content of the FA is evidenced by a halo between angles 17° 2θ and 33° 2θ. However, the precise quantification of the reactive content in coal fly ash type F is not straightforward, as demonstrated by Kuenzel and Ranjbar [41], who divided the FA into three In terms of mineralogy, the X-ray diffraction analysis of the FA showed a main presence of quartz and mullite. The amorphous content of the FA is evidenced by a halo between angles 17 • 2θ and 33 • 2θ.…”

“…The amorphous content of the FA is evidenced by a halo between angles 17 • 2θ and 33 • 2θ. However, the precise quantification of the reactive content in coal fly ash type F is not straightforward, as demonstrated by Kuenzel and Ranjbar [41], who divided the FA into three different materials: reactive, partially reactive, and inert. They showed that the contribution of the cenospheres (i.e., partially reactive fraction) is restricted to the outer layer, which makes it almost impossible to accurately quantify the overall contribution.…”

Curing Time and Temperature Effect on the Resistance to Wet-Dry Cycles of Fly Ash Added Pumice Based Geopolymer

“…Therefore, if the curing temperature and time increases, the Si/Al ratio increases in the initial reaction environment. For fly ash as precursor material, the Si/Al mass ratio of the dissolved materials increased from initially 3.8 to 5.3 within 24 h when the dissolution temperature is 65 °C [17]. Further, dissolution type namely congruent or incongruent may be important for geopolymerisation process.…”

“…It is reported that the curing temperature (25-145 °C) and time (2-24h) highly effects the dissolution of precursor aluminosilica material independent of alkali metal solution molarity in the range of 8-16M. This situation is explained as increasing in the kinetic energy of the system at elevated temperatures and so the solvent molecules breaks the solute molecular bonds and hold an intermolecular attraction, more efficiently [17]. In order for geopolymer reactions to take place properly and to accelerate, initially enough amount with a suitable ratio of precursor material must be dissolved in the reaction medium.…”

Sustainable Development and Performance Evaluation of Marble-Waste-Based Geopolymer Concrete

“…Geopolymers (GPs) belong to the category of novel inorganic polymers that are cementitious alumino-silicates, demonstrating an amorphous three-dimensional (3D) structure and made up of AlO 4 and SiO 4 tetrahedral units linked by shared oxygen atoms [ 11 ]. Geopolymerization is an exothermic reaction among precursors rich in alumina and silica of either industrial or geological origin with concentrated alkali activators in a combined solution of silicate and alkali hydroxide [ 7 , 12 , 13 ], at a temperature ranging from as low as ambient or even room temperature up to 100 °C and at an atmospheric pressure [ 14 , 15 , 16 ]. Geopolymeric composites demonstrate outstanding and unique characteristics in terms of durability, higher initial strength and mechanical properties; resistance to attack by chemicals like sulfates and acids; fire and thermal stability at elevated temperatures; exceptional resistance to freeze/thaw; anti-corrosion behavior; a carbon footprint that is nine times lower [ 16 , 17 , 18 ] and an energy use that is six times lower than current systems of OPC production [ 11 ]; little shrinkage; the ability to be cured by autoclave, etc., making them attractive alternatives to conventional systems [ 8 , 19 , 20 ].…”