Performing Department
Bioresource Science and Engineering
Non Technical Summary
Cross-laminated timber (CLT) panels represent a new and innovative engineered wood product that is rapidly gaining acceptance in Europe, Canada and Japan. However, the development of a CLT industry in the US has been slowed by a number of factors. One issue that has restricted the adoption of CLT construction in the US has been concern with its fire performance, and ability to comply with fire codes in cities. Another issue has been concern about the durability of CLT panels when exposed to moisture in exterior applications. This project aims to improve the fire and moisture performance of CLT panels through the use of two new and innovative technologies that have never been applied to CLT panels. The successful application of these innovative technologies, the thermal modification of lumber and carbon-based nanomaterials, would radically change the landscape for CLT panels and significantly speed their adoption and diffusion within the low-to-medium rise buildings sector.
Animal Health Component
0%
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
The overall goal of this project is to assess the effectiveness of thermal modification (TM) and carbon-based nanoparticles (CBN) processes in improving the fire resistance of western hemlock lumber as an overlay on cross laminated timber (CLT) wall panels. The research objectives are: i) determine the impact of the thermal modification process on hemlock lumber, ii) evaluate the effectiveness of TM and CBN in improving the fire resistance of wood panels, and iii) estimate the life cycle impacts of replacing traditional exterior sheathing materials (e.g., steel and concrete) with CLT panels treated with a CBN fire resistant coating.
Project Methods
TASK 1: The Interfor sawmill (in Port Angeles, Washington) will donate kiln dried hemlock lumber for the study. Each piece of lumber will be cut into control and sample specimens that will be measured for straightness prior to the thermal modification (TM) process. Half of the specimens will be shipped to the Natural Resources Research Institute at the University of Minnesota in Duluth (UMD-NRRI) for TM treatment while the remaining control specimens will be shipped to the WSU Composite Materials and Engineering Center to produce untreated hemlock panels.TASK 2: UMD-NRRI will thermally modify the hemlock lumber at a high temperature in a vacuum evacuated kiln in the presence of steam. During the TM process, much of the hemicelluloses are driven from the wood. Upon completion of the process, the samples will be conditioned in a standard environment before being shipped to WSU. The research team will measure each TM specimen to evaluate the impact of the TM process on lumber straightness. The influence of TM on the bending strength of the TM hemlock lumber will be evaluated. The bending strength test specimens will be the full width and thickness of the lumber with the length being set so that a 16-1 span to depth ratio is achieved for flexural testing in the flatwise direction. The sample size for the mechanical testing will be 50 specimens for each of the control and treatment groups (100 specimens total). Third-point bending to failure will be performed on the bending specimens. Load and deflection data will be acquired, with the flexural properties being computed.TASK 3: Layers of graphene will be prepared by the direct exfoliation of graphite in aqueous media under tip sonication with the assistance of alkali lignin. Commercially available multi-wall carbon nanotubes will be purified using a combination of non-oxidative acid soaking and annealing in air to remove amorphous carbon and metal residues. Four different mixtures of CBN will be prepared using the following mass ratios of graphene:nanotube: 3:1, 2:1, 1:1, and 1:2. Thermogravimetric analysis (TGA) in air will be used to determine the thermo-oxidative stability of the CBN mixtures based upon their graphene:nanotube mass ratios and the two most promising specimens will then be used for the coating of a thin protective layer on both untreated and TM hemlock panels. The CBN coatings will be applied with a spray deposition procedure using an airbrush system. The influence of the different deposition parameters and their potential interactions on the mass, thickness and distribution of CBN will be thoroughly studied based on a statistical design of experiment approach. The mass of the protective CBN layer will be determined by the change in mass measured by a laboratory microbalance of the specimens stored in a desiccator before and after coating. The coating thickness, the distribution of nanoparticles and the overall quality of the coating will be qualitatively evaluated by scanning electron microscopy (SEM).TASK 4: Following the testing of the CBN treatments, the UW team will produce test panels that are 3 foot by 3 foot by 1.5 inches in thickness. The test panels will be produced to allow four types of testing regimes: 1) four panels will be assembled using untreated hemlock lumber (H), 2) four panels will be assembled using thermally modified hemlock lumber (TM), 3) four panels will be assembled using untreated hemlock lumber with a layer of carbon-based nanoparticles deposited onto the surface of the panel (H/CBN) and 4) four panels will be assembled using thermally modified hemlock lumber with a layer of carbon-based nanoparticles deposited onto the surface of the panel (TM/CBN). CBN will be coated on the external surface of the H/CBN and TM/CBN panels using a spray deposition procedure which is a highly scalable and cost-effective manufacturing technique for applying thin layers. TASK 5: A series of different tests will be conducted to examine the flammability and thermostability of the wood panels. Before each test, all specimens will be conditioned in a climate chamber with controlled humidity level. Four replicates of each sample will be analyzed to ensure reproducible and significant data. First, the combustion behavior will be investigated by cone calorimetry. This test will provide a thorough comparison of the heat release rate and total burn time across specimens. It will be completed by typical vertical burning tests to observe the self-propagation of a flame on each specimen. The depth of char and the amount of smoked produced will also be quantified. These observations are important because they can uncover potential melt dripping phenomena which can significantly increase the fire threat. Furthermore, the gas permeability of the different specimen will also be characterized by measuring the time necessary for a known amount of gas at ambient conditions to diffuse through the structure of interest into a dynamic vacuum greater than 3×10−3 mbar. The pressure drop will be measured using a gas manometer and the effective diffusivities of O2, N2, and CO2 will be compared. Then, the ability of the different specimens employed as wall and partition systems to stop the spread of flames and/or hot gases from penetrating through the panel assembly will be investigated. These tests will be evaluated under various time of exposure and temperature. Finally, the microstructure of the CBN coatings and char residues will be systematically studied both before and after each fire resistance test. The morphology and chemical structure of the CBN coatings will be assessed by scanning electron microscopy (SEM) and Raman/FTIR/UV-Vis spectroscopy.TASK 6: A preliminary comparative life cycle assessment (LCA) will be conducted to compare the TM/CBN wood panels against traditional concrete and steel exterior sheathing systems in cooperation with the USDA Forest Products Lab. Three subtasks will be performed: (i) modify our existing CLT LCA to make it specific to the Olympic Peninsula, (ii) establish the LCA for TM/CBN CLT panels, and (iii) compare the environmental footprint of TM/CBN CLT panels against traditional concrete and steel exterior wall systems. The research team will undertake an environmental footprint analysis of the upstream forestry activities based on key life cycle datasets. The environmental footprint associated with thermal modification and a cradle to gate LCI for the proposed CBN process will be developed. The overall cradle to gate (construction site) LCA for TM-CBN CLT panels will then be developed. The comparative LCA analysis of the exterior wall systems will be undertaken between wall systems with comparable thermal insulation (R-value) and structural properties, suitable for low to mid rise buildings. We will compare a traditional concrete and steel exterior wall system, a regular CLT wall system and a TM/CBN wall system, with an effective R-value of 4.5 RSI. The traditional steel and concrete exterior wall system is generally an exterior metal cladding with metal furring, extruded polystyrene, polyethylene air barrier, steel studs and rockwool and gypsum. A regular CLT exterior wall system would include an exterior metal cladding (for fire code compliance) with metal furring, two layers of wood studs and cavity rock, followed by CLT panels coated with waterproofing material. The TM/CBN CLT exterior wall system eliminates the use of the exterior metal cladding, waterproofing material, polystyrene and steel studs. The comparative LCA analysis will provide a comprehensive and practical environmental analysis of the CBN coated TM-CLT exterior wall system. Note that the elimination of the traditional cladding will significantly reduce the construction time and material requirements, resulting in greater economic efficiency during construction.