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 characterization of coal fly ash-based foamed geopolymer

Abstract: Fly ash, a residue arising from the combustion of pulverized coal, is one of the major wastes generated in coal-fired power stations Several utilization options of fly ash are currently being practised in many countries in an effort to minimize waste and protect the environment This paper studied the potential use of fly ash from South African power utilities in the production of foamed geopolymeric materials which may be suitable for various applications including the building industry The foamed geopolymers were synthesized through alkali activation of the fly ash and subsequent hydrothermal treatment procedure This was done by mixing fly ash (FA) with sodium hydroxide (NaOH) and ultrapure water to form a paste, before introducing sodium hypochlorite solution (NaOCl, foaming agent) into the existing paste The resulting mixture was then placed in the oven to produce the foamed geopolymer The mixing was done using FA: NaOH: NaOCl: H2O mass ratio of 303: 100: 114: 100 The chemical composition, mineralogy, morphology and molecular structure of the starting material (fly ash) and the synthesized product (foamed geopolymer) were analyzed using XRF, XRD, SEM and FTIR respectively The porosity and the bulk density of the foamed geopolymer was also determined using mercury porosimetry

Atomistic Simulations of Geopolymer Models: The Impact of Disorder on Structure and Mechanics

Abstract: Geopolymers are hydrated aluminosilicates with excellent binding properties. Geopolymers appeal to the construction sector as a more sustainable alternative to traditional cements, but their exploitation is limited by a poor understanding of the linkage between chemical composition and macroscopic properties. Molecular simulations can help clarify this linkage, but existing models based on amorphous or crystalline aluminosilicate structures provide only a partial explanation of experimental data on the nanoscale. This paper presents a new model for the molecular structure of geopolymers, in particular for nanoscale interfacial zones between crystalline and amorphous nanodomains, which are crucial for the overall mechanical properties of the material. For a range of Si-Al molar ratios and water contents, the proposed structures are analyzed in terms of skeletal density, ring structure, pore structure, bond-angle distribution, bond length distribution, X-ray diffraction, X-ray pair distribution function, elastic moduli, and large-strain mechanics. Results are compared with experimental data and with other simulation results for amorphous and crystalline molecular models, showing that the newly proposed structures better capture important structural features with an impact on mechanical properties. This offers a new starting point for the multiscale modeling of geopolymers.

Preparation of phosphoric acid-based geopolymer foams using limestone as pore forming agent – Thermal properties by in situ XRPD and Rietveld refinements

Abstract: In this work, geopolymer foams were obtained by reacting metakaolin with phosphoric acid and using natural calcite/dolomite as foaming agent. Total porosity and thermal conductivity were ca. 70% and 0.083 ± 0.008 W/mK, respectively. Rietveld refinements, using both ex - and in situ XRPD data, were performed in order to elucidate the phase stability of the formed binder up to 1200 °C. The results showed that the amorphous matrix partially crystallized in tridymite and cristobalite type structures of AlPO 4 –SiO 2 solid solutions at about 700 °C. At 1000 °C, 3:2 mullite started to crystallize, possibly from unreacted metakaolinite, resulting in co-crystallization of SiO 2 cristobalite. At the same time, the amount of tridymite-type structure decreased, possibly due to selective phase transformation of AlPO 4 tridymite to cristobalite, leaving behind the SiO 2 isostructure. The geopolymer paste composition allows to tailor the mullite content in the refractory foam.