Consequential life cycle assessment of activated hydrochar-enhanced cement plaster from municipal waste

This study presents a comprehensive life cycle assessment (LCA) of a novel cement-lime-based plaster incorporating 4 wt% activated hydrochar (AHYP), produced via hydrothermal carbonization of the stabilized organic fraction (SOF) of municipal solid waste (MSW) using landfill leachate as the process medium. A consequential LCA approach, following ISO 14040/14044 standards, was adopted to capture the broader environmental consequences of substituting conventional materials and streams with waste-derived alternatives. Two system levels were assessed: a cradle-to-gate analysis per kilogram of plaster produced, and a cradle-to-grave comparison of a 4 cm application on both sides of a reference building façade. Cradle-to-gate results identified the activation process as the most impactful stage in AHYP production. However, the benefits of avoiding waste treatment and energy savings outweighed these burdens compared to conventional cement-lime plaster (CP). Further, at the cradle-to-grave scale, AHYP reduced climate change impacts by 68% over a 50-year lifespan, driven by biogenic carbon sequestration, carbonation, avoided landfill emissions, and improved thermal efficiency. Evaluation of alternative scenarios (AS) reinforced the consistency and reliability of the findings. Higher methane recovery rates from landfill up to 50% (AS1-50%), and 64% (AS1-64%), as well as the halving of plaster's service life to 25 years (AS2) and changing gas boilers with electric heating technologies (AS3), were investigated. While these alternatives (AS1-50%, AS1-64%, AS2, AS3) slightly increased impacts relative to the Inn-Scenario, they consistently performed better than the Ref-Scenario, underscoring the sustained environmental benefits observed across different conditions. Overall, results demonstrate the promising role of hydrochar-based plasters as a circular and climate-conscious alternative in the construction sector.