Physicochemical structure and micromechanical properties of archaeological wood under alternating dry and wet conditions

The relationship between physicochemical structure and micromechanical properties of archaeological wood is not understand. For this purpose, the study took the archaeological wood from the Shahe Ancient Bridge site as an example. The physical properties, microstructure, chemical composition, and micromechanics of archaeological wood were evaluated using non-destructive and micro-destructive techniques. The results indicated that the deterioration of Phoebe sp. wood was more severe than that of Abies sp. wood. However, the basic density of Phoebe sp. wood was higher than that of the control sample due to the collapse of cell walls. The cell walls exhibited a variety of destructional forms, such as cavities and collapses, caused by decay fungi and erosion bacteria. The cell cavities and cell walls deposited inorganic substances. Furthermore, hemicellulose and amorphous cellulose were preferentially degraded before crystalline cellulose was degraded, and S-type lignin was more prone to degradation compared to G-type lignin. Due to the changes of cell wall structure, the hardness of the cell walls increased while the elastic modulus of the cell wall decreased significantly. This study may provide a reference for the study of the relationship between cell wall structure and micromechanics of archaeological wood.