BONDING HARDWOOD LUMBER FOR CROSS LAMINATED TIMBER: PROPERTIES AND ENVIRONMENTAL IMPACTS

Cross-laminated timber (CLT) is a prefabricated engineered wood product that are made of at least three orthogonal layers of graded sawn lumber or structural composite lumber (SCL) that are laminated by gluing with structural adhesives. The concept of CLT has been developed into a global adaptable building material. The advancement rates of CLT as mass building material in production volume and distribution has unwrapped up new opportunities for hardwood species, which traditionally have not been extensively used for structural engineering applications. The objectives of this research are to provide key information on engineering performance, as well as baseline data on the adhesion properties of bonding northern hardwood species and their environmental impacts. The methodology used in this study followed specific standard guidelines including; the Standard for performance-rated CLT panels (ANSI/APA PRG-320-2012; 2016), the Standard Test Method for Strength Properties of Adhesive Bonds in Shear by Compression Loading (ASTM D905), Standard Practice for Estimating the Percentage of Wood Failure in Adhesive Bonded Joints (ASTM D5266), the Standard Specification for Adhesives for Bonded Structural Wood Products for Use Under Exterior Exposure Conditions (ASTM D2559), Test Methods for Structural Glued Laminated Timber (AITC Test 2007) and ISO 14044 on the environmental management- life cycle assessment requirements and guidelines. The results showed that bonding strength is positively related to wood density; high density diffuse-porous species (such as hard maple and yellow birch) have low percentage of wood failure when used in single species or mixed with each other for CLT production. The average bonding shear strength of cross-laminated mixed hardwoods was 5% (P85%) from the small block test was very high. Although, there was record of individual hard maple sample blocks recording very low percentage wood failure (\u3e25%). The results from the bending tests are promising since the experimental results show that both hard maple CLT and hard maple-spruce hybrid CLT meets and exceed the shear and bending strength requirements in ANSI/APA PRG-320-2012 CLT Grade E3. The major failure modes found were shear failure, bottom splint and delamination. Finally, the cradle-gate life cycle analysis of hardwood and softwood CLT indicated that resorcinol (PRF) and hardwood combinations have the highest environmental impact (10300 and 60900 Kg CO2 eq; 1890000 MJ and 1140000 MJ of total energy consumed respectively). Comparably, softwood has less environmental impact compared to hardwood in CLT manufacturing and melamine base adhesive has a reduction of 34% of energy demand and 11% in GWP when bonded with softwood compared to a combination with hardwoods bonded with resorcinol. Over 70% of the energy in CLT was from non-renewable sources