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Review
. 2020 Jul 17;13(14):3198.
doi: 10.3390/ma13143198.

Natural Fiber-Stabilized Geopolymer Foams-A Review

Katharina Walbrück  1 , Felicitas Maeting  1 , Steffen Witzleben  1 , Dietmar Stephan  2
Affiliations
Review

Natural Fiber-Stabilized Geopolymer Foams-A Review

Katharina Walbrück et al. Materials (Basel). .

Abstract

The development of sustainable, environmentally friendly insulation materials with a reduced carbon footprint is attracting increased interest. One alternative to conventional insulation materials are foamed geopolymers. Similar to foamed concrete, the mechanical properties of geopolymer foams can also be improved by using fibers for reinforcement. This paper presents an overview of the latest research findings in the field of fiber-reinforced geopolymer foam concrete with special focus on natural fibers reinforcement. Furthermore, some basic and background information of natural fibers and geopolymer foams are reported. In most of the research, foams are produced either through chemical foaming with hydrogen peroxide or aluminum powder, or through mechanical foaming which includes a foaming agent. However, previous reviews have not sufficiently addresses the fabrication of geopolymer foams by syntactic foams. Finally, recent efforts to reduce the fiber degradation in geopolymer concrete are discussed along with challenges for natural fiber reinforced-geopolymer foam concrete.

Keywords: geopolymer foam; natural fiber; thermal insulation material.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Classification of thermal insulation materials according to Reference [2].
Scheme 1
Scheme 1
Hypothetical reaction mechanism for orthosialate ions according to Reference [20].
Figure 2
Figure 2
Classification of natural fibers according to Reference [47].
Figure 3
Figure 3
FTIR spectra of (a) untreated hemp; (b) NaOH-treated hemp; (c) NaOH + Al2(SO4)3 treated hemp; and (d) precipitate or residue from the spend solution of Al2(SO4)3 treatment. Reprinted from Reference [51] under open access license.
Figure 4
Figure 4
Influence of nano-sillica content on flexural and compressive strength of geopolymer samples according to Reference [14].
Figure 5
Figure 5
Scanning electron microscopy (SEM) images of flax fiber-reinforced geopolymer concrete; (a) geopolymer with flax fibers, (b) geopolymer with flax fibers and nano-silica (dry-mix) (c) geopolymer with flax fibers and nano-silica (wet-mix). Reprinted from Reference [57] under open access license.
Figure 6
Figure 6
Optical microscopy and SEM characterization of fly ash geopolymers produced with different amounts of H2O2 as foaming agent ((a) and (f) 0.03 wt. %, (b) and (g) 0.15 wt. %, (c) and (h) 0.30 wt. %, (d) and (i) 0.90 wt. % and (e) and (j) 1.20 wt. %). Reprinted from Reference [42], © 2020, with permission from Elsevier.
Figure 7
Figure 7
Micro-tomography images of geopolymer foams produced with H2O2 as a foaming agent. Reprinted from Reference [81], © 2020, with permission from Elsevier.
Figure 8
Figure 8
Micro-tomography images of geopolymer foams produced with Al powder as a foaming agent. Reprinted from Reference [81], © 2020, with permission from Elsevier.
Figure 9
Figure 9
Porosity and thermal conductivity of geopolymers with different amounts of H2O2, according to Reference [73].
Figure 10
Figure 10
Influence of the metakaolin/fly ash ratio on dry density and compressive strength according to Reference [73].
Figure 11
Figure 11
Influence of the amount of H2O2 on dry density and compressive strength according to Reference [73].
Figure 12
Figure 12
Porosity and thermal conductivity of geopolymers with different water-to-solid ratios according to Reference [86].
Figure 13
Figure 13
Foam stabilization via (a) a surfactant and Pickering emulsion formulated from (b) nanoparticles (c) fibers and (d) surfactant–fiber–nanoparticle (SFN) according to Reference [101].
See this image and copyright information in PMC

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