Characterization of Fly Ash Alkali Activated Foams Obtained Using Sodium Perborate Monohydrate as a Foaming Agent at Room and Elevated Temperatures

Abstract

Alkali activated foams have been extensively studied in recent years, due to their high performance and low environmental footprint compared to foams produced via other methods. Three types of fly ash differing in chemical and mineralogical composition and specific surface were used to synthesize alkali activated foams. Sodium perborate monohydrate was added as a foaming agent and sodium dodecyl sulphate as a stabilizing agent. Foams were characterized at room temperature and after exposure to an elevated temperature (1,000°C). Densities from 1.2 down to 0.3 g/cm 3 were obtained, depending on the type of fly ash and quantity of foaming agent added. Correspondingly, compressive strength ranged from 1 to 6 MPa. Comparing all three fly ashes the most favorable results, in terms of density and corresponding compressive strength, were achieved from the fly ash with the highest amounts of SiO 2 and Al 2 O 3 , as well as the highest amorphous phase content i.e., RI fly ash. Furthermore, after firing to 1,000°C, the density of samples prepared using fly ash RI remained approximately the same, while the compressive strength increased on average by 50%. In the other two types of fly ash the density increased slightly after firing, due to significant shrinkage, and compressive strength increased by as much as 800%. X-ray powder diffraction analysis confirmed the occurrence of a crystallization process after firing to 1,000°C, which resulted in newly formed crystal phases, including nepheline, sodalite, tridymite, and gehlenite.

Investigation on pore properties, thermal conductivity, and compressive behavior of fly ash/slag‐based geopolymer foam

“…It is nearly two times the maximum cube strength and more than 2.5 times the maximum cylinder strength obtained with the help of foam stabilizer. 45 To sum up, in comparison with the FA-based geopolymer foams reported in the literature, the FA/GGBFS geopolymer foam prepared in the study generally possesses not only a comparable thermal conductivity but also a far superior compressive strength.…”

“…As far as the ther-mal conductivity and compressive strength are concerned, seven studies measured both thermal conductivity and total porosity, and 11 studies measured both compressive strength and total porosity. 11,36,[39][40][41][42][43][44][45][46][47] To focus on the porous geopolymer, the comparisons were limited in the range of total porosities larger than 45%. Figure 8 presents the thermal conductivities and compressive strengths of the selected geopolymer foams.…”

“…As a result, a total of 52 datasets were assembled from 14 studies for comparison. [9][10][11]37,38,[43][44][45][46][48][49][50][51][52] Figure 9 collects the compressive strengths of the geopolymer foams. Generally, the proposed geopolymer foams exhibit superior compressive strength even in comparison to the FA/GGBFS geopolymer foams reported in the literature, except for the one with a thermal conductivity of .21 W/mK.…”

The EU Training Network for Resource Recovery through Enhanced Landfill Mining—A Review

“…This paper was cited in publications on the preparation of glass-containing foams from geopolymers [122] and vitrified MSWI bottom ash [123] in which the formation of wollastonite and the freezing of the microstructural evolution were mentioned. Other papers cited this publication with respect to the recycling of glass waste into foam glass [124][125][126][127][128][129], porous waste glass for lead removal in wastewater treatment [130], lead stabilization through alkali activation and sintering of Pb-bearing sludge [131], utilization of waste glass for the production of sulphuric acid resistant concrete [132], mechanical and alkali activation of MSWI fly and bottom ashes for the production of low-range alkaline cement [133] and foam glass-ceramics [134], inorganic gel casting for manufacturing of boro-alumino-silicate glass foams [135], porous glass-ceramics derived from MgO-CuO-TiO 2 -P 2 O 5 glasses [136], alkali activation of coal and biomass fly ashes [137], nickel-based catalysts for steam reforming of naphthalene utilizing MSW gasification slag as support [138], production of porous glass ceramics from titanium mine tailings and waste glass [139], porous bioactive glass microspheres [140], Al-SiO 2 composites [141], glass-ceramic foams from alkali-activated vitrified MSWI bottom ash and waste glasses [142]. Another study used vitrified MSWI bottom ash as input material to obtain similar porous glass ceramics [143] and was cited by some of the publications that also cited the first study.…”

Environmental and Biological Impact of Fly Ash and Metakaolin-Based Alkali-Activated Foams Obtained at 70°C and Fired at 1,000°C

“…Especially, alkali-activated foams (AAFs) seem to be promising because they can be obtained at temperatures well below 100°C but offering performance similar to foamed glass or aerated concrete ( Ducman and Korat, 2016 ). Porosity is introduced by different foaming agents, like hydrogen peroxide ( Masi et al, 2014 ; Abdollahnejad et al, 2015 ), perborate, ( Korat and Ducman, 2020 ), and metals ( Masi et al, 2014 ; Hlavacek et al, 2015 ; Kamseu et al, 2015 ), which decompose or react in alkaline mixture, forming gasses at the proper stage of fresh paste induration to create a porous structure. Density as low as 0.3 g/cm 3 could be achieved by this method, whereas porosity significantly influences mechanical performance.…”