Role of thermo-alkaline-oxidized kraft lignin aided by concrete waste as a potential reinforcement material in botanical concrete.

• Complete waste recycling is achieved by botanical concrete. • Mechanism of using kraft lignin (KL) as a reinforcement material is identified. • Alkaline oxidation of KL aided by concrete promotes the condensation of KL. • Low chemical condensation potential of KL should be utilized. Exploring the bonding mechanism of botanical concrete (BC), which is developed by crushing concrete, wood waste and kraft lignin (KL) and hot pressing the obtained powder, aids in comprehending its formation and enhancing performance. This study continues the attempts on this subject, focusing on the microstructural changes between KL and concrete. Herein, the chemical structural transformations in the mixtures of KL with three sources of powder (concrete, carbonated concrete, and sand) during hot pressing are evaluated by FTIR, XRD, TGA, and 13C NMR methodologies. These results show that BC strength is affected by depolymerization, fragmentation, and crosslinking reactions that alter the chemical bonds within KL. Condensation reactions between concrete and KL fragments, facilitated by air, are the most influential factor in improving BC strength. Waste concrete with alkalinity promotes the oxidation of KL and subsequent crosslinking, offering a new perspective for further development of self-bonding lignin-based materials. [ABSTRACT FROM AUTHOR]