Hydrothermally Treated Biomass Fly Ash as an Additive for Portland Cement

Abstract

This study aimed to investigate the possibility of using biomass fly ash as a cement additive after hydrothermal modification. The treatment of biomass fly ash involves additional milling and curing under various hydrothermal conditions. Variation of the CaO/SiO2 ratio was achieved by mixing different samples of biomass fly ash. Samples with a CaO/SiO2 ratio of 1 and 1.5 were selected for synthesis, and cement samples with different amounts of the synthesized additive were examined. The research employed the following methodologies: XRD, XRF, DSC-TG, ICP-OES, and isothermal calorimetry. It was found that in all the biomass fly ash samples, calcium silicate hydrates already formed after 2 h of hydrothermal synthesis at 200 °C. Analysis of the chemical composition of the liquid medium after hydrothermal maintenance revealed an exceptionally low release of heavy metals from the samples. The synthesised additive accelerated the initial hydration of Portland cement. In total, 5% to 10% of the weight of cement can be replaced by hydrothermally treated biomass fly ash without reducing the compressive strength class of Portland cement samples.