The dry shrinkage and wet swelling properties of structural bamboo scrimber with holes

HUANG Zilan;WU Yue;WANG Zhiqiang;ZHU Yixin;College of Materials Science and Engineering, Nanjing Forestry University;

structural bamboo scrimber;;hole;;dry shrinkage rate;;wet swelling rate

The dry shrinkage and wet swelling properties associated with bamboo have been studied extensively, but limited studies associated with bamboo scrimber are found according to the literature review. In this study, the iterative optimal threshold method was used to process the scanned images into binary images, and Image Pro Plus and Photoshop were used to examine the dimensional changes of structural bamboo scrimbers with radial or tangential holes in different diameters. During the drying or soaking processes, the dry shrinkage and wet swelling rates of bamboo scrimbers with holes and the variation rate of hole area were investigated, the k-value, and the ratio of the vertical axis(perpendicular to the grain) to the horizontal axis(parallel to the grain) were also analyzed. The correlations between the moisture content and the radial or tangential dimensions, hole area and k-value were investigated to provide a basis for the design of bamboo scrimbers with holes in construction projects. The results showed that the radial and tangential dry shrinkage rates of bamboo scrimbers were 1.14% and 1.56%, and the radial and tangential wet swelling rates were 1.49% and 3.38%, respectively. The radial and tangential dry shrinkage rates of the hole area were 1.18% and 1.24%, and the radial and tangential wet swelling rates were-1.14% and 2.42%, respectively. The radial and tangential dry shrinkage k-values of the holes were 97.09% and 94.86%, respectively, and the radial and tangential swelling k-values were 98.60% and 97.89%, respectively. The dry shrinkages or wet swelling rates and k-values of bamboo scrimbers with different radial hole diameters(6, 10 and 14 mm) were significant different. The variation in hole dia-meter had no significant effect on the dry shrinkage and wet swelling properties of bamboo scrimbers with holes but had a significant effect on the variation in the shape of the holes themselves. The moisture content of bamboo scrimbers showed a linear growth trend with respect to dimensional growth rate and hole area, and an exponential growth trend with regard to hole axis ratio. The dimensional stability of bamboo scrimber members with tangential holes was better than those with radial holes. The stability of hole area variation was better for tangential holes than that for radial holes, while the shape stability of radial holes was better than that of tangential holes. The dry shrinkage effect of the holes due to the change in moisture content was more intense than that of the wet swelling effect.