Chemical characterisation of metakaolin and fly ash based geopolymers during exposure to solvents used in carbon capture

•Geopolymer construction materials are partially leached by carbon capture solvents.•Alteration processes in water, K2CO3 and MEA follow different pathways.•Binder mineralogy is altered by solvents, leading to zeolite formation.•K2CO3 leads to formation of carbonate deposits within the binder phases. This paper presents an investigation into the chemical resistance of blended alkali activated aluminosilicate materials, specifically under exposure to two solvents used in post-combustion carbon capture, monoethanolamine (MEA) and potassium carbonate, as well as during immersion in distilled water. Geopolymers are formulated based on metakaolin and on fly ash as aluminosilicate precursors, with the addition of ground granulated blast furnace slag (GGBFS) as a source of Ca. The samples are subjected to mineralogical and chemical characterisation in this paper, with data obtained through leaching analysis and X-ray diffraction, supported by compressive strength data. Exposure to solvents generally results in significant alteration of the geopolymer microstructure. The zeolitic phases formed in undamaged metakaolin-based binders are reduced to undetectable levels after 28 days of solvent exposure, although the hydrosodalite formed in the fly ash binders does persist. Leaching analysis indicates that resistance to structural damage in MEA is quite high, due to the low solubility of Na and hydroxides upon immersion. K2CO3 solutions are aggressive towards geopolymers via alteration of the binder structure and dissolution of network-forming species (Si and Al), leading to the loss of binder strength. This is most marked in the fly ash/GGBFS formulations. Despite the low to intermediate level of Ca present in these geopolymer binders, significant formation of Ca-containing carbonate phases occurs upon exposure to K2CO3. The limited curing duration of the specimens tested here is certainly contributing to the degradation taking place under K2CO3 exposure, whereas the low water activity in the MEA solutions used means that bond hydrolysis in the aluminosilicate geopolymer framework is restricted, and the materials perform much better than in a more water-rich environment.