Quality assessment and mechanical characterization of preservative-treated Moso bamboo (P. edulis)

Bamboo has been in the focus of attention as a re-discovery of an old and available material to solve environmental problems in the construction industry. The use of full-culm bamboo in the built environment, however, depends on proper quality control/assurance of its mechanical and physical properties. In this work, a quality assessment in terms of treatment control and mechanical properties of a small production of Phyllostachys edulis bamboo poles treated with disodium octaborate tetrahydrate (DOT) was performed. A comparison between two commercial preservatives used for exterior and interior applications, chromated copper borate (CCB) and DOT respectively, in terms of the effect on the mechanical properties and treatability behaviour was also investigated. Penetration and retention analyses showed satisfactory results for the samples treated with CCB, with retention of 7.2 kg/m³, while lower values of retention for the samples treated with DOT by the immersion method (2.2 kg/m³) was observed. Microstructural and EDS analyses revealed a much higher concentration of chromium and copper from the CCB solution in the bamboo large vessels. The mechanical characterization performed by compression, shear, tension, coupon three-point bending, and flat ring flexure tests showed that the difference between the two treatment conditions was small and, in most cases, not statistically relevant. Low coefficients of variation were observed in all the investigated mechanical tests, suggesting a uniform distribution of mechanical properties within the batch of P. edulis bamboo used in this study. The full characterization schedule combined with digital image correlation analyses enabled the calculation of the characteristic values of the mechanical properties, useful for structural design, complementing the treatability and quality assessment.