Additive manufacturing with geopolymer foams: A critical review of current progress

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Chemical contents of industrial waste as an aluminosilicate source_

Chemical composition (%)	Fly ash	Slag	Silica fume
SiO2	52.31	39.8	92.05
Al2O3	28.59	11.2	0.72
Fe2O3	6.22	1.2	1.31
CaO	4.01	34.4	0.46
MgO	2.05	7.6	—
K2O	1.62	—	1.51
SO3	1.79	0.46	0.41
N2O	—	0.2	0.45
References	[37]	[10]	[38]

Effect of foaming agents on the compressive strength and density_

Foaming agent	Compressive strength and density	Ref.
H2O2	Increasing H2O2 concentration from 1 to 3.5% in geopolymer foam leads to a decrease in compressive strength (44.81–3.2 MPa) and density (1,021–142 kg/m3)	[94]
	Using 0.1–1% H2O2 reduces the compressive strength from 5.9 to 0.26 MPa and the apparent density from 1,100 to 230 kg/m3	[95]
Al powder	The use of Al powder with increasing percentages of 0.01–0.15% reduces the compressive strength (42.0–4.6 MPa) and density (1,830–1,031 kg/m3)	[64]
	1.5–5.0% of Al powder decreases the compressive strength from 4.35 to 0.9 MPa and density from 1,309 to 403 kg/m3	[96]

Reference relationships among density, compressive strength, porosity, and thermal conductivity of geopolymer foam_

Precursor	FA	SA	Density (kg/m3)	Compressive strength (MPa)	Porosity (%)	Thermal conductivity (W/(m k))	Ref.
Metakaolin	H2O2	Olive oil	320–610	0.2–3.9	75–87	0.147	[103]
Metakaolin	Na2O2	SDBS	300–460	0.6–1.6	72–81	0.085–0.115	[104]
Fly ash	H2O2	—	240–340	0.60–0.38	79–81	0.09–0.07	[105]
Metakaolin	H2O2	—	470–1,210	0.37–6.00	36–86	0.11–0.30	[97]
FA, GGBS	SDS	RCA	824–838	1.3–1.8	42–71	0.270–0.360	[106]
Metakaolin	SLES	—	690–1,060	4.7–14.8	56–72	0.197–0.364	[107]
FA, POFA	Sika AER	—	1,300–1,700	8–13	25–40	0.47–0.50	[74]
FA	H2O2	CSFS	310–380	1.45–1.60	70–82	0.095–0.139	[108]
FA	H2O2	Calcium stearate	150–240	0.45–0.75	88.94–91.94	0.0485–0.0594	[109]
FA	H2O2	Calcium stearate	200–300	1.06–2.84	59–83	0.05223–0.0711	[110]
HCFA	Natural protein	—	844–2,100	2.7–57.8	2.82–49.42	0.13–1.62	[111]
Metakaolin	H2O2	Vegetable oil	370–740	0.3–11.6	66–83	0.11–0.17	[67]
Metakaolin	H2O2	Tween 80	300–750	0.3–9.4	67–86	0.289–0.091	[112]

Effect of agent material on the porosity of geopolymer foam_

Material agent	Effect on porosity	Ref.
Foaming agent	The addition of aluminum powder at concentrations of 0.07–0.2% increased porosity from 47.9 to 58.4%, while H2O2 at 0.5–2% enhanced porosity from 37.9 to 44.9%	[101]
	Increasing the H2O2 concentration from 1 to 3.5% in geopolymer foam increased the porosity from 32.3 to 63.1%	[94]
Stabilizing agent	Tween 80 as a surfactant, with a concentration ranging from 1 to 5%, increased the porosity from 38 to 86%	[97]
	Using olive oil as a stabilizing agent at concentrations ranging from 1.25 to 15% with the same H2O2 concentration reduced the porosity from 75.1 to 72.3%	[67]
Alkaline solution	Increased ratio of NaOH to Na2SiO3 enhanced the porosity from 55.6 to 66.3% while maintaining the same foaming agent concentration	[99]
	Increasing the Na2O ratio from 4 to 7% in an alkaline solution increased the porosity of the structure from about 61.6 to 68%	[11]