Development of sustainable building technologies from out-of-grade timber

Development of sustainable building technologies from out-of-grade timber

The study investigated the structural and bond performance of out-of-grade Pinus elliotti var. elliottii (Engelm) x Pinus caribaea var. hondurensis (Sénéclauze) (PEExPCH) hybrid pine, to provide information necessary to make informed decisions on incorporating this abundant and underutilised building material into sustainable building solutions. An in-depth critical review of the literature was completed and provided an understanding of the challenges, strengths and opportunities of out-of-grade pine. Cross laminated timber (CLT) was identified as an opportunity for using large volumes of out-of-grade timber and therefore investigated as an example in this research of a sustainable building system solution for utilisation of out-of-grade PEExPCH. An extensive experimental study was completed to investigate the structural properties of out-of-grade PEExPCH and the impact of commonly occurring characteristics of resin, knots and pith. Clear samples contained no major defect other than occasional occurrence of pith, resin contained naturally occurring heavy resin deposits in the timber and the third sample type contained knots, these were further separated into samples with and without pith. There was equal representation of each of these three sample types in tests completed. Modulus of elasticity (MOE) and strengths were determined and compared on a total of 105 bending, 105 compression parallel to grain, 105 compression perpendicular to grain, 90 longitudinal shear and 135 rolling shear samples. 105 samples were tested for tensile strength. Engineered wood products, such as CLT, rely on their glue lines to perform reliably and consistently over time in service and therefore bond performance was also assessed. After an accelerated aging process, 30 five-layer cross laminated timber (CLT) samples glued with onecomponent polyurethane glue (PUR) were assessed for delamination and wood failure. Additionally, 160 bond line shear tests in glulam orientation and 192 in CLT orientation were conducted, both of which are options for bond line assessment in EN16351(2015) CLT standard. 16 large-scale specimens were tested for bending MOE and strength to evaluate the performance of CLT made from out-of-grade PEExPCH. Wood and wood-based reinforcements were used to evaluate their effect on increasing bending properties including high-grade timber and plywood. Testing was performed according to AS4063.1:2010 and modified planar shear test was used for rolling shear performance. The results showed that the bending MOE of the out-of-grade PEExPCH is low at around 6.9 GPa and is the predominant reason for not achieving highly sought after structural grades. Resin achieved between 98% and 116% of the structural performance of clear samples while, knots achieved between 46% to 196% of clear samples. Pith achieved between 75% and 121% of non-pith, had higher density and had a mixed effect on structural properties. Growth ring pattern had a significant effect on rolling shear properties. Clear out-of-grade PEExPCH had good bond performance results with 3% delamination, 96% wood failure, 8.5 GPa bond line shear strength as Glulam, 4.0 MPa bond line shear strength as CLT and a 100% pass rate under two international CLT standards. Resin and knots had a negative impact on delamination and wood failure while pith experienced premature wood failures. The bending MOE and strength of CLT were low at 6.2 GPa and 24.9 MPa, respectively. The use of high-grade timber as reinforcement in the outer layers provided the largest improvement on both bending MOE and strength with increases of 53% and 93%, respectively. Using the mechanical properties determined in this study, the shear analogy method predicted bending MOE to within 11% of that measured in the experimental study. The results of this study can provide valuable information for the timber and building and construction industries for design, product development, optimisation and manufacture utilising out-of-grade PEExPCH. For example, the results show that for structural applications there is no need to treat resinous timber differently to clear when looking to achieve MOE and strength targets for most properties. Whereas, if minimising self-weight is a critical design factor then excluding resinous timber would be beneficial. All timber has mechanical properties and if looking to source a low cost timber population to low stress applications within building systems such as noggings, bottom plates of single story houses or partition walls in some applications, the structural properties determined through this research informs engineers of their capacity to withstand design loads to determine their suitability to perform safely in these applications. The safe use of this out-of-grade timber in place of in-grades makes better use of the entire log, reduces waste providing a more sustainable solution, in some instances may reduce lead times because out-of-grade timber is readily available and can also provide a cost saving as out-of-grade timber is less expensive. Some restriction is needed on knots for structural performance requirements and knots, resin and pith for bond performance requirements.

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