Geopolymer

About: Geopolymer is a research topic. Over the lifetime, 6776 publications have been published within this topic receiving 157991 citations. The topic is also known as: geopolymers.

Synthesis and properties of inorganic polymers (geopolymers) derived from Bayer process residue (red mud) and bauxite

Abstract: Well-reacted geopolymers with good compressive strengths (44–58 MPa) were formed from highly alkaline residue from red mud (the residue remaining after extraction of alumina from bauxite by the Bayer Process) without the addition of strength-promoting components, such as fly ash or ground slag, by adjusting the composition to an optimal SiO2/Al2O3 ratio of about 3 with silica fume. The formation of these geopolymers is extremely energy-efficient since thermal dehydroxylation of the red mud is not required. The environment of the Si and Al in the geopolymers was shown by 27Al and 29Si NMR spectroscopy to be consistent with reasonably well-reacted aluminosilicate materials, suggesting that the red mud forms geopolymers by reaction of aluminate and silicate species in a process not dissimilar to that of alkali-activated kaolin. The presence of high concentrations of iron in the red mud principally in the form of hematite did not interfere with geopolymer formation, since it was shown by XRD and Mossbauer spectroscopy to remain largely unaltered and not participate in the reaction. Analogous experiments with bauxite from which red mud is derived by alkali treatment, produce geopolymers of significantly lower strength (up to 28 MPa), suggesting that the action of the alkali during bauxite processing facilitates the formation of the geopolymer binder, possibly by increasing the reactivity of the red mud, as occurs in alkali-treated kaolinite.

High-temperature behavior of polyvinyl alcohol fiber-reinforced metakaolin/fly ash-based geopolymer mortar

Abstract: Polyvinyl alcohol (PVA) fiber-reinforced geopolymer mortar is an eco-friendly construction material with excellent mechanical properties and durability. Visual observation, mass loss measurement, cubic and prism compressive tests , flexural tests, thermogravimetric and differential thermal analysis , scanning electron microscopy, and bubble parameter tests were conducted to evaluate the effect of PVA fiber and exposure temperature on the behavior of PVA fiber-reinforced geopolymer mortar after exposure to high temperatures. The PVA fiber contents were selected as 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, and 1.2%, and the target temperatures were 25 °C, 200 °C, 400 °C, 600 °C and 800 °C. The results indicate that significant mass loss of the geopolymer mortar could be observed when the exposure temperature increased from 25 °C to 250 °C, whereas slight mass loss occurred from 250 °C to 700 °C, and no mass loss was detected from 700 °C to 800 °C. As the temperature increased, the geopolymer mortar gradually densified, while the geopolymer mortar continuously developed more cracks and pores. The compressive and flexural strengths of the geopolymer mortar improved as the temperature increased from 25 °C to 200 °C, but it decreased significantly as the temperature further increased to 800 °C. In addition, on exposure to 200 °C, the presence of PVA fibers significantly improved the cubic and prism compressive strengths and flexural strength by 50.5%, 29.4%, and 66.3%, respectively, compared with the geopolymer mortar without fibers. As the temperature increased above 200 °C, although the PVA fiber decomposed, the defects left by the melt fibers slightly influenced the strength of the geopolymer mortar.