Effects of Iron Minerals on the Compressive Strengths and Microstructural Properties of Metakaolin-Based Geopolymer Materials

Abstract

The current study aims to investigate the influence of iron minerals on the amorphous phase content, compressive strengths and the microstructural properties of the geopolymer materials. Geopolymer materials were prepared by the substitution of metakaolin by 10 and 20 wt.% of each iron mineral sample. Sodium waterglass from rice husk ash was used as a hardener, and metakaolin was used as an aluminosilicate source. The X-ray patterns show that the iron minerals denoted FR and FB are associated with hematite and magnetite, respectively. FY contains goethite together with a significant content of kaolinite and quartz. It is observed in the XRD patterns and FTIR absorption spectra that the additions of hematite, magnetite and goethite remain largely unreacted in the geopolymer binder. The compressive strengths of the related geopolymer composites show some significant variations indicating certain effects for mechanical stability obtained: 10 wt.% replacement of metakaolin by hematite increased the compressive strength from 51.1 to 55.5 MPa, while 20 wt.% hematite caused a decrease to 44.9 MPa. Furthermore, 10 and 20 wt.% replacement with FB revealed decreased values 47.0 and 40.3 MPa, respectively. It was also found that 10 and 20 wt.% of FY caused lower values of 30.9 and 39.1 MPa, respectively. The micrographs of geopolymer materials present some voids and cracks. The denser matrix is related to a superior gel formation producing a better glue between the crystalline additions. The unsubstituted geopolymer sample provides with about 50% the highest X-ray-amorphous content, whereas the substituted samples range between 35 and 45%, indicating systematically smaller gel contents without any clear trend with the compressive strength variation, however. The strength dependencies reveal more complex interaction between the gel and crystalline additions.

Investigation of the Properties of Metakaolin-Based Geopolymer Materials Using Ferrisilicates as Additives Synthesised in Sodium Hydroxide Solution or Distilled Water

“…The iron source in the form of hematite, designation F, was supplied by Serraciments Company (Barcelona, Spain). This iron oxide has been used by Ngnintedem et al [8] as an additive for the synthesis of geopolymer materials. They reported that the broadening of the peak shows that the average size of the crystals of hematite is 120 nm.…”

“…Eggshell, bauxite, and rice husk ash are used as sources of calcium, alumina, and silica, respectively, for the preparation of additives. The effect of different iron minerals such as hematite, magnetite, and goethite on the compressive strength of geopolymer cement was investigated by Ngnintedem et al [8]. It was reported that a 10 wt% addition of hematite to metakaolin resulted in a compressive strength of 56 MPa.…”

Microstructure and Compressive Strength of Geopolymer Materials Based on Metakaolin with Hematite and Magnetite Gels as Additives

“…15,16 Iron oxide, like hematite powder, has been reported to act as a filler by several authors. 17 Several authors have reported that iron oxide, as well as hematite powder, contained in or added to feedstocks used to synthesise geopolymer materials, acts as a filler. The result is that there is no dissolution of the hematite during the geopolymerisation process.…”

Estudo do desempenho mecânico de geopolímero produzido com auto teor de ferro

“…A composição mineralógica do material de partida influencia em uma maior resistência do geopolímero, que pode ser obtida quando apresentam uma alta taxa de dissolução ou através da calcinação das matériasprimas [13]. Outro exemplo, o teor de ferro presentes em minerais de ferro como hematita, magnetita, maghemita, goethita, limonita e entre outros, que são encontrados em quantidades significativas de fontes de aluminossilicatos, também afetam as propriedades mecânicas dos geopolímeros [14].…”

“…O comportamento do ferro na reação de geopolimerização depende de qual estado físico e mineralógico o ferro está contido na matéria-prima [21,22]. NGNINTEDEM et al [14] investigaram a influência de três minerais de ferro, sendo estes a hematita, magnetita e goetita, na resistência à compressão em materiais geopoliméricos à base de metacaulim. Foi observado uma maior resistência nos geopolímeros contento hematita e magnetita em comparação com os contendo goetita.…”