A physical approach towards controlling the microstructure of metakaolin-based geopolymer foams

Abstract

Geopolymer foams are promising sustainable lightweight materials combining insulation efficiency with interesting mechanical and fire resistance properties. Controlling their pore size remains challenging because intrinsic foam aging processes act before hardening. We highlight a physical approach to counteracting aging processes in fresh geopolymer foams and to maintaining the pore morphology that has been set initially by mixing metakaolin suspension with precursor aqueous foam. More precisely, it is shown that arrest of foam aging can be achieved if solid particle concentration in the suspension is larger than a critical value which is proved to depend on both bubble size and gas volume fraction. This behavior is understood through the jamming transition occurring for the metakaolin suspension when confined in the foam network, providing significant solid elasticity against bubble motions. The general significance of the reported result makes it useful, as a complement to chemical formulation, for designing morphology-controlled geopolymer foams.

Effects of surfactants/stabilizing agents on the microstructure and properties of porous geopolymers by direct foaming

“…Therefore, samples with same amount of additional H 2 O (11 wt%, z = 11) using different types of surfactants were also investigated. Figures 2-4 Previous works [34][35][36] showed that the nature of the surfactant plays an important role in the fabrication of porous geopolymers by direct foaming. Indeed, different surfactants showed different foaming ability for the geopolymer slurry (see Figures 2-4 (a, a) (z = o) and Figures 2-4 (c, c) (z = 11)).…”

Determination of the Influence of Hydraulic Additives on the Foaming Process and Stability of the Produced Geopolymer Foams

“…This material is also referred to as foam concrete, which by definition is a cellular concrete with a large number of hollow spaces, with or without the addition of aggregate [ 9 ]. They have good thermal insulation and acoustic properties [ 10 , 11 , 12 , 13 ] as well as mechanical properties, although their compressive strength is lower than that of solid (not foamed) geopolymers [ 10 , 14 ]. The comparison of fire-resistant properties of geopolymers and other materials is shown in Figure 1 [ 15 ].…”

Acoustics of monodisperse open-cell foam: An experimental and numerical parametric study

“…Therefore, numerous works are still devoted to elucidate the link between their microstructure and their macroscopic properties, such as thermal, acoustical, mechanical, and transport properties (Despois and Mortensen, 2005;Doutres et al, 2011;Gibson and Ashby, 1997;Jang et al, 2008;Kumar and Topin, 2014). Recently, mineral solid foams, made from cement or geopolymer or gypsum, have been studied for their applications as building materials, requiring a good compromise between mechanical strength, and sound and/or thermal insulation (Chevillotte et al, 2013;Feneuil et al, 2019;Hung et al, 2014;Kaddami and Pitois, 2019;Zhang et al, 2014). This kind of solid foam differs from polymeric foams, which are widely used for sound and/or thermal insulation by both their wide range of porosity (from 0.65 to 0.95) and their highly stiff porous frames.…”

“…A millifluidic setup, described in detail in Kaddami and Pitois (2019), is used to generate monodisperse foam (Fig. 3).…”

“…To prevent the ripening in the case of the smallest sizes (0.2 and 0.3 mm), nitrogen used as bubbling gas in the precursor foam production was saturated in perfluorohexane vapor (Gandolfo and Rosano, 1997). To ensure the stability of the fresh foam before the geopolymer setting, particular attention was paid to the choice of geopolymer formulation, as shown in detail in Kaddami and Pitois (2019). However, despite our special care, a small and unexpected drainage was observed for high solid volume fraction (/ s տ 0:3) leading to a low gradient of solid volume fraction.…”