Abstract
The growing interest of using industrial waste as recycled raw materials for the production of new, innovative materials is associated with effective use of natural resources and circular (zero-waste) economy. The research object is waste stream materials coming from chemical and processing industries, such as aluminium scrap recycling waste, chamotte-like precursor, firebricks sawing residues, and their use in production of high-temperature resistant, porous insulation materials by using alkali activation technique with 6M NaOH solution. Adding aluminium scrap recycling waste to the composition of the tested alkali activated materials (AAM) contributed to the porous structure of the material with the pore size ranging from 1000 – 5000 µm (detected by Micro-XCT, SEM)). Lightweight (350-850 kg/m3) and heat-resistant (up to 1000°C) AAM with compressive strength from 1.0 to 3.0 MPa was obtained. The mineralogical composition of the obtained AAM was detected (XRD) and the heat resistant minerals in the structure of AAM were identified. It was concluded that the increased amount of Al2O3 in the raw material composition resulted in improved thermal stability of the AAM. In case where SiO2/Al2O3 ratio is <2, the formation of high-temperature resistant minerals, such as carnegeite and nepheline, was observed. The obtained AAM could resist up to 8 thermal shock cycles and it could be easily adapted to the industrial production and application such as thermal insulation layer in laboratory furnaces.
Highlights
Low calcium alkali activated materials (AAM) or “Geopolymers” in some cases are the terms used to describe aluminosilicatebased inorganic polymers produced by mixing pozzolanic compounds or aluminosilicate source precursors and highly alkaline solutions (Davidovits, 1991)
The resistance to high temperatures of AAM strongly depends from the composition of raw materials, i.e., Dupuy et al has reported that all argillite-based AAM samples show low resistance to thermal shock (800◦C, 10 min) and strength decreased up to 10 times (Dupuy et al, 2018), while other report by K
DTA/TG The changes of AAM during heat treatment up to 1,200◦C could be described in four distinct phases (Figure 2)
Summary
Low calcium alkali activated materials (AAM) or “Geopolymers” in some cases are the terms used to describe aluminosilicatebased inorganic polymers produced by mixing pozzolanic compounds or aluminosilicate source precursors and highly alkaline solutions (Davidovits, 1991). Many factors can contribute to the alkali activation reaction mechanism and the properties of the final products, including (but not limited to) the aluminosilicate source precursors (Bumanis et al, 2017), the type of activator solution (Criado et al, 2007), the calcium content in the raw material mixture composition (Canfield et al, 2014), and the mixing and curing conditions (Moukannaa et al, 2018) as well as pore forming process (Bajare et al, 2014; Strozi et al, 2014; Seabra et al, 2016). Aungkavattana states that thermal shock resistance of metakaolin-based AAM at temperature of 800◦C could reach up to 15 cycles (Hemra and Aungkavattana, 2016). In comparison with traditional refractory brick performance these results seems promising as their thermal shock resistance varies from 10 to 30 cycles (Philip, 2014)
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