Thermal and hygroscopic expansion characteristics of bamboo

The expansion and contraction of bamboo caused by temperature and moisture variations must be evaluated if bamboo is to be utilised as a building material. However, detailed expansion data, especially data in the ascent and descent processes of temperature and moisture are unexplored. The aim of this study is to investigate the expansion characteristics of Phyllostachys edulis (Moso bamboo) in ascent and descent processes of temperature and moisture. The measurement of linear thermal expansion and hygroexpansion of bamboo specimens were conducted with a dilatometer and a micrometer, respectively. The temperature range of the linear thermal expansion measurement was between 23 and 70°C. In the linear moisture expansion measurement, all specimens were measured at various relative humidity (RH) conditions including oven dry, 27, 54, 76 and 95%RH, and water soaking stages. Major findings include: the swell of bamboo specimens increases with RH, whereas the shrinkage of bamboo specimens decreases with RH. The hygroexpansion is much more significant compared with the linear thermal expansion. Both linear thermal expansion and hygroexpansion of the specimens from the longitudinal directions are smaller than those from the radial direction and tangential direction.