The synthesis and characterization of geopolymers based on metakaolin and high LOI straw ash

Abstract Incompletely combusted biomass ash containing unburned carbon is very often complemented by polycyclic aromatic hydrocarbons (PAHs). The straw ash containing PAHs, marked as hazardous waste, has been used as a filler in metakaolin-based geopolymers with the purpose of studying the quality of its incorporation and its influence on the resulting properties. The obtained data have shown that although the mineralogical composition of geopolymers with straw ash added is almost identical, the results of compressive strength indicate some differences between the samples depending on the amount of ash added and the setting temperature. The pH measurement has confirmed a significant decrease in the original ash value (11.52) after ash addition into the geopolymer matrix. Fourier transform infrared spectroscopy (FTIR) has proven the formation of geopolymer bonds by alkaline activation even after ash addition. The inhibition of PAHs has been verified through their extraction and determination, with the results showing a significant reduction in the amount of the PAHs detected.