North American cross laminated timber is currently made of softwood lumber following the guidelines of the ANSI/APA PRG-320 manufacturing standard. In this study, the potential of manufacturing CLT panels using various hardwood species and engineered wood products (EWP) was investigated for their compatibility and the impact on the dimensional stability and aesthetics of the end products. Yellow birch, trembling aspen, sugar maple, laminated strand lumber (LSL) and laminated veneer lumber (LVL) were compared to 100% spruce-pine-fir group species (SPF) lumber made CLT panel. The bond line performance of the assemblies was tested as well as the dimensional stability and appearance of the panels when subjected to conditions with equilibrium moisture contents (EMC) of 4.5%, 12% and 16%. Results showed that higher density hardwood species were prone to delamination. LSL, LVL and trembling aspen yielded promising delamination results. Best overall dimensional stability results were achieved with EWP inclusive configurations. Aesthetic integrity assessment showed that the use of hardwood for the core layer and edge gluing of softwood outer layers had a negative impact. Overall, the study showed a great potential for manufacturing future composite CLT (CCLT) products using EWP and low density hardwood species. The cost premium of using these alternative materials would need to be offset by valuable sets of properties or by a reduction of the manufacturing cost.
Solid-sawn lumber (Douglas-fir, southern pine, Spruce– Pine–Fir, and yellow-poplar), laminated veneer lumber (Douglas-fir, southern pine, and yellow-poplar), and laminated strand lumber (aspen and yellow-poplar) were heated continuously at 82°C (180°F) and 80% relative humidity (RH) for periods of up to 24 months. The lumber was then reconditioned to room temperature at 20% RH and tested in edgewise bending. Little reduction occurred in modulus of elasticity (MOE) of solid-sawn lumber, but MOE of composite lumber products was somewhat reduced. Modulus of rupture (MOR) of solid-sawn lumber was reduced by up to 50% after 24 months exposure. Reductions in MOR of up to 61% were found for laminated veneer lumber and laminated strand lumber after 12 months exposure. A limited scope study indicated that the results for laminated veneer lumber in edgewise bending are also applicable to flatwise bending. Comparison with previous results at 82°C (180°F)/25% RH and at 66°C (150°F)/20% RH indicate that differences in the permanent effect of temperature on MOR between species of solid-sawn lumber and between solid-sawn lumber and composite lumber products are greater at high humidity levels than at low humidity levels. This report also describes the experimental design of a program to evaluate the permanent effect of temperature on flexural properties of structural lumber, with reference to previous publications on the immediate effect of temperature and the effect of moisture content on lumber properties.
The objective of this study is to evaluate the fire behavior of CLT manufactured with different types of SCL or lumber boards, namely with laminated veneer lumber (LVL), laminated strand lumber (LSL) and Trembling Aspen. The fire test data is also compared to those of CLT manufactured in accordance with ANSI/APA PRG-320 using solid-sawn lumber grades. More specifically, the study aims at evaluating the charring rates of this new generation of CLT panels as well as the impact of their manufacturing parameters.
The in-plane permeability was measured for thick, unidirectional oriented strand lumber made from aspen (Populus tremuloides) strands and pressed to five different densities. The press cycle was such that the vertical density profile of the panels was uniform. Specimens were cut from the boards and sealed inside a specially designed specimen holder; this jig was connected to a permeability measurement apparatus and in-plane permeability measured parallel, perpendicular, and 45° to the strand orientation. Permeability decreased markedly with increasing board density. The highest permeability was in the strand alignment direction and lowest perpendicular to it. The permeability in the 45° direction fell between those in parallel and perpendicular to strand alignment. A polynomial equation was fit to the results of each direction with r2 of 0.938 and 0.993. The in-plane distribution of permeability as a function of flow direction was obtained and its vector diagram was lenticular in shape.
CLT is an engineered wood product made from 3-7 layers of lumber assembled with alternating grains. Typically softwood lumber is used to manufacture CLT, but as Aspen (Populus tremuloides) lumber is highly available in Minnesota, this study was performed to investigate its feasibility for use in CLT panels. A CLT panel was manufactured using locally-acquired aspen lumber and tested for flatwise bending properties. A maximum load of 20.98 kN was found for the panel, which exceeds the standard [9]. However, the values found for MOE and MOR of 8,068 MPa and 13.26 MPa, respectively, were below those of the standard. This research was supported by the Undergraduate Research Opportunities Program (UROP).
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