Development of advanced materials from industrial waste, with high thermal performance

•Valorization of metallurgical by-products (copper slag).•Production of geopolymer foams with thermal insulating and fire resistance properties.•Enhancement of geopolymer foams mechanical properties with cement and silica fume addition in the mixture.•Quantification of porosity in the produced materials. The aim of this study is the production of advanced fire-resistant components using the industrial residue of a Swedish mining and smelting company Boliden (copper slag). The main objective of this experimental work is the assessment of the appropriate conditions for the preparation of alkali activated geopolymer pastes with further foaming production, by blowing agent addition. The alkaline activating solution that was used was potassium hydroxide [KOH] at a constant concentration (8 M) while aluminum powder [Al powder] was selected as the foaming agent (0.15 wt % of the paste). The solid to liquid ratio was equal to 3.5 g/mL. The elucidation of the valorization potential of copper slag’s substitution with cement (0–29 wt % to slag) was also tested. The physical properties of the materials were examined after the appropriate curing process (24 h at 70 °C), with density values ranging between 805 and 917 kg/m3. The mechanical performance of selected materials was also investigated and the results revealed that the partial substitution of cement on slag, enhanced the mechanical performance of the materials. When slag was mixed with cement at the maximum ratio (29 wt % to slag), the compressive and flexural strength of the produced specimens reached 2 MPa and 0.78 MPa, respectively. Despite of the improvement on mechanical properties due to the cement’s addition in the mixture, the values are still quite low. Thus, further investigation of the geopolymer synthesis took place, substituting a part of cement with silica fume [Si fume] (7 wt % to cement). Eventually, Si fume addition led to materials with similar like physical properties, but with higher compressive and flexural strength values (4.7 and 0.95 MPa respectively) after long lasting hardening, due to the Si fume’s property to act as a micro filler in function of time. The final materials were also evaluated as for their fire resistance, proving to withstand under the time – temperature curves of ISO – 834. To assess the porosity and the size distribution of the voids, image processing techniques were applied on digital images of the samples. According to these results, the synthesized materials exhib