Hydrothermal Carbonization of Residual Biomass for Functional Hydrochars in Emission Reduction of Bituminous Materials

This study investigates the use of hydrochar as a bio-based functional additive for the mitigation of volatile organic compound (VOC) emissions from bituminous binders. The work contributes to the development of more sustainable construction materials through the valorisation of locally available residual biomass and the reduction of hazardous fume emissions associated with asphalt production and paving operations. Hydrothermal carbonization (HTC) was applied to the invasive aquatic biomass Myriophyllum aquaticum, converting it into a carbon-rich hydrochar under operating conditions selected to maximise carbon yield (200 °C, 30 min, 25 wt% solid load). The produced hydrochar, characterised by 50.31 wt% carbon content and elemental ratios H/C = 1.11 and O/C = 0.42, was incorporated into bitumen at 10 wt% and evaluated through headspace gas chromatography–mass spectrometry analysis. Compared to virgin bitumen, the hydrochar-modified binder exhibited a 23.9% reduction in total VOC emissions and a 25.4% reduction in the cumulative content of the most toxic VOCs. The results demonstrate the potential of converting invasive biomass into functional carbon materials for internal emission control in bituminous products, supporting circular resource use and the transition toward lower-emission road infrastructure.