Enhancing performance and achieving carbon negativity in botanical concrete via autoclave pre-treatment and high kraft lignin addition

The substantial environmental footprint of conventional concrete and the escalating volume of construction and demolition waste necessitate urgent development of novel, sustainable building materials. Cement-free botanical concrete (BC), made from concrete and wood waste, promotes closed-loop recycling but suffers from poor water resistance and dimensional instability. This study investigates autoclave pre-treatment (12 conditions) of wood particles and high kraft lignin (KL; 30–70 wt%) addition to improve the performance of BC. Optimal autoclaving (160–180 °C, 5 min) minimized swelling to 7 %. Results revealed that the combined approach significantly enhanced the water resistance of BC. However, high KL content (>30 wt%) improved water resistance, it reduced bending strength. Furthermore, a life cycle assessment (LCA) confirmed the carbon-negative potential of the developed BC, identifying key emission hotspots and suggesting further reduction measures. These findings highlight the potential of modified BC in sustainable construction and guide the development of environmentally friendly building materials.